Network Working Group J. Sermersheim
Internet-Draft Novell, Inc
Expires: January 18, 2006 L. Poitou
Sun Microsystems
July 17, 2005
Password Policy for LDAP Directories
draft-behera-ldap-password-policy-09.txt
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
Password policy as described in this document is a set of rules that
controls how passwords are used and administered in Lightweight
Directory Access Protocol (LDAP) based directories. In order to
improve the security of LDAP directories and make it difficult for
password cracking programs to break into directories, it is desirable
to enforce a set of rules on password usage. These rules are made to
ensure that users change their passwords periodically, passwords meet
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construction requirements, the re-use of old password is restricted,
and users are locked out after a certain number of failed attempts.
Discussion Forum
Technical discussion of this document will take place on the IETF
LDAP Extensions mailing list <ldapext@ietf.org>. Please send
editorial comments directly to the authors.
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Table of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Application of password policy . . . . . . . . . . . . . . . . 6
4. Articles of password policy . . . . . . . . . . . . . . . . . 7
4.1 Password Usage Policy . . . . . . . . . . . . . . . . . . . . 7
4.2 Password Modification Policy . . . . . . . . . . . . . . . . . 7
4.3 Restriction of the Password Policy . . . . . . . . . . . . . . 10
5. Schema used for Password Policy . . . . . . . . . . . . . . . 11
5.1 The pwdPolicy Object Class . . . . . . . . . . . . . . . . . . 11
5.2 Attribute Types used in the pwdPolicy ObjectClass . . . . . . 11
5.3 Attribute Types for Password Policy State Information . . . . 16
6. Controls used for Password Policy . . . . . . . . . . . . . . 21
6.1 Request Control . . . . . . . . . . . . . . . . . . . . . . . 21
6.2 Response Control . . . . . . . . . . . . . . . . . . . . . . . 21
7. Policy Decision Points . . . . . . . . . . . . . . . . . . . . 23
7.1 Locked Account Check . . . . . . . . . . . . . . . . . . . . . 23
7.2 Password Must be Changed Now Check . . . . . . . . . . . . . . 23
7.3 Password Expiration Check . . . . . . . . . . . . . . . . . . 23
7.4 Remaining Grace AuthN Check . . . . . . . . . . . . . . . . . 23
7.5 Time Before Expiration Check . . . . . . . . . . . . . . . . . 24
7.6 Intruder Detection Check . . . . . . . . . . . . . . . . . . . 24
7.7 Password Too Young Check . . . . . . . . . . . . . . . . . . . 24
8. Server Policy Enforcement Points . . . . . . . . . . . . . . . 25
8.1 Password-based Authentication . . . . . . . . . . . . . . . . 25
8.2 Password Update Operations . . . . . . . . . . . . . . . . . . 27
8.3 Other Operations . . . . . . . . . . . . . . . . . . . . . . . 30
9. Client Policy Enforcement Points . . . . . . . . . . . . . . . 31
9.1 Bind Operation . . . . . . . . . . . . . . . . . . . . . . . . 31
9.2 Modify Operations . . . . . . . . . . . . . . . . . . . . . . 32
9.3 Add Operation . . . . . . . . . . . . . . . . . . . . . . . . 33
9.4 Compare Operation . . . . . . . . . . . . . . . . . . . . . . 33
9.5 Other Operations . . . . . . . . . . . . . . . . . . . . . . . 34
10. Administration of the Password Policy . . . . . . . . . . . . 35
11. Password Policy and Replication . . . . . . . . . . . . . . . 36
12. Security Considerations . . . . . . . . . . . . . . . . . . . 37
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38
14. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 39
15. Normative References . . . . . . . . . . . . . . . . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 40
Intellectual Property and Copyright Statements . . . . . . . . 41
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1. Overview
LDAP-based directory services are currently accepted by many
organizations as the access protocol for directories. The ability to
ensure the secure read and update access to directory information
throughout the network is essential to the successful deployment.
Most LDAP implementations support many authentication schemes - the
most basic and widely used is the simple authentication i.e., user DN
and password. In this case, many LDAP servers have implemented some
kind of policy related to the password used to authenticate. Among
other things, this policy includes:
o Whether and when passwords expire.
o Whether failed bind attempts cause the account to be locked.
o If and how users are able to change their passwords.
In order to achieve greater security protection and ensure
interoperability in a heterogeneous environment, LDAP needs to
standardize on a common password policy model. This is critical to
the successful deployment of LDAP directories.
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2. Conventions
Imperative keywords defined in [RFC2119] are used in this document,
and carry the meanings described there.
All Basic Encoding Rules (BER) [X690] encodings follow the
conventions found in Section 5.1 of [RFC2251].
The term "password administrator" refers to a user that has
sufficient access control privileges to modify users' passwords. The
term "password policy administrator" refers to a user that has
sufficient access control privileges to modify the pwdPolicy object
defined in this document. The access control that is used to
determine whether an identity is a password administrator or password
policy administrator is beyond the scope of this document, but
typically implies that the password administrator has 'write'
privileges to the password attribute.
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3. Application of password policy
The password policy defined in this document can be applied to any
attribute holding a user's password used for an authenticated LDAP
bind operation. In this document, the term "user" represents any
LDAP client application that has an identity in the directory.
This policy is typically applied to the userPassword attribute in the
case of the LDAP simple authentication method [RFC2251] or the case
of password based SASL [RFC2222] authentication such as CRAM-MD5
[RFC2195] and DIGEST-MD5 [RFC2831].
The policy described in this document assumes that the password
attribute holds a single value. No considerations are made for
directories or systems that allow a user to maintain multi-valued
password attributes.
Server implementations MAY institute internal policy whereby certain
identities (such as directory administrators) are not forced to
comply with any of password policy. In this case, the password for a
directory administrator never expires; the account is never locked,
etc.
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4. Articles of password policy
The following sections explain in general terms each aspect of the
password policy defined in this document as well as the need for
each. These policies are subdivided into the general groups of
password usage and password modification. Implementation details are
presented in Section 8 and Section 9.
4.1 Password Usage Policy
This section describes policy enforced when a password is used to
authenticate. The general focus of this policy is to minimize the
threat of intruders once a password is in use.
4.1.1 Password Guessing Limit
In order to prevent intruders from guessing a user's password, a
mechanism exists to track the number of consecutive failed
authentication attempts, and take action when a limit is reached.
This policy consists of five parts:
o A configurable limit on failed authentication attempts.
o A counter to track the number of failed authentication attempts.
o A timeframe in which the limit of consecutive failed
authentication attempts must happen before action is taken.
o The action to be taken when the limit is reached. The action will
either be nothing, or the account will be locked.
o An amount of time the account is locked (if it is to be locked).
This can be indefinite.
4.2 Password Modification Policy
This section describes policy enforced while users are modifying
passwords. The general focus of this policy is to ensure that when
users add or change their passwords, the security and effectiveness
of their passwords is maximized. In this document, the term "modify
password operation" refers to any operation that is used to add or
modify a password attribute. Often this is done by updating the
password attribute during an add or modify operation, but MAY be done
by other means such as an extended operation.
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4.2.1 Password Expiration, Expiration Warning, and Grace
Authentications
One of the key properties of a password is the fact that it is not
well known. If a password is frequently changed, the chances of that
user's account being broken into are minimized.
Password policy administrators may deploy a password policy that
causes passwords to expire after a given amount of time - thus
forcing users to change their passwords periodically.
As a side effect, there needs to be a way in which users are made
aware of this need to change their password before actually being
locked out of their accounts. One or both of the following methods
handle this:
o A warning may be returned to the user sometime before his password
is due to expire. If the user fails to heed this warning before
the expiration time, his account will be locked.
o The user may bind to the directory a preset number of times after
her password has expired. If she fails to change her password
during one of her 'grace' authentications, her account will be
locked.
4.2.2 Password History
When the Password Expiration policy is used, an additional mechanism
may be employed to prevent users from simply re-using a previous
password (as this would effectively circumvent the expiration
policy).
In order to do this; a history of used passwords is kept. The
password policy administrator sets the number of passwords to be
stored at any given time. Passwords are stored in this history
whenever the password is changed. Users aren't allowed to specify
any passwords that are in the history list while changing passwords.
4.2.3 Password Minimum Age
Users may circumvent the Password History mechanism by quickly
performing a series of password changes. If they change their
password enough times, their 'favorite' password will be pushed out
of the history list.
This process may be made less attractive to users by employing a
minimum age for passwords. If users are forced to wait 24 hours
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between password changes, they may be less likely to cycle through a
history of 10 passwords.
4.2.4 Password Quality and Minimum length
In order to prevent users from creating or updating passwords that
are easy to guess, a password quality policy may be employed. This
policy consists of two general mechanisms - ensuring that passwords
conform to a defined quality criterion and ensuring that they are of
a minimum length.
Forcing a password to comply with the quality policy may imply a
variety of things including:
o Disallowing trivial or well-known words make up the password.
o Forcing a certain number of digits be used.
o Disallowing anagrams of the user's name.
The implementation of this policy meets with the following problems:
o If the password to be added or updated is encrypted by the client
before being sent, the server has no way of enforcing this policy.
Therefore, the onus of enforcing this policy falls upon client
implementations.
o There are no specific definitions of what 'quality checking'
means. This can lead to unexpected behavior in a heterogeneous
environment.
4.2.5 User Defined Passwords
In some cases, it is desirable to disallow users from adding and
updating their own passwords. This policy makes this functionality
possible.
4.2.6 Password Change after Reset
This policy forces the user to update her password after it has been
set for the first time, or has been reset by a password
administrator.
This is needed in scenarios where a password administrator has set or
reset the password to a well-known value.
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4.2.7 Safe Modification
As directories become more commonly used, it will not be unusual for
clients to connect to a directory and leave the connection open for
an extended period. This opens up the possibility for an intruder to
make modifications to a user's password while that user's computer is
connected but unattended.
This policy forces the user to prove his identity by specifying the
old password during a password modify operation.
{TODO: This allows a dictionary attack unless we specify that this is
also subject to intruder detection. One solution is to require users
to authN prior to changing password. Another solution is to perform
intruder detection checks when the password for a non-authenticated
identity is being updated}
4.3 Restriction of the Password Policy
The password policy defined in this document can apply to any
attribute containing a password. Password policy state information
is held in the user's entry, and applies to a password attribute, not
a particular password attribute value. Thus the server SHOULD
enforce that the password attribute subject to password policy,
contains one and only one password value.
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5. Schema used for Password Policy
The schema elements defined here fall into two general categories. A
password policy object class is defined which contains a set of
administrative password policy attributes, and a set of operational
attributes are defined that hold general password policy state
information for each user.
5.1 The pwdPolicy Object Class
This object class contains the attributes defining a password policy
in effect for a set of users. Section 10 describes the
administration of this object, and the relationship between it and
particular objects.
( 1.3.6.1.4.1.42.2.27.8.2.1
NAME 'pwdPolicy'
SUP top
AUXILIARY
MUST ( pwdAttribute )
MAY ( pwdMinAge $ pwdMaxAge $ pwdInHistory $ pwdCheckQuality $
pwdMinLength $ pwdExpireWarning $ pwdGraceAuthNLimit $ pwdLockout
$ pwdLockoutDuration $ pwdMaxFailure $ pwdFailureCountInterval $
pwdMustChange $ pwdAllowUserChange $ pwdSafeModify ) )
5.2 Attribute Types used in the pwdPolicy ObjectClass
Following are the attribute types used by the pwdPolicy object class.
5.2.1 pwdAttribute
This holds the name of the attribute to which the password policy is
applied. For example, the password policy may be applied to the
userPassword attribute.
( 1.3.6.1.4.1.42.2.27.8.1.1
NAME 'pwdAttribute'
EQUALITY objectIdentifierMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.38 )
5.2.2 pwdMinAge
This attribute holds the number of seconds that must elapse between
modifications to the password. If this attribute is not present, 0
seconds is assumed.
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( 1.3.6.1.4.1.42.2.27.8.1.2
NAME 'pwdMinAge'
EQUALITY integerMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
SINGLE-VALUE )
5.2.3 pwdMaxAge
This attribute holds the number of seconds after which a modified
password will expire.
If this attribute is not present, or if the value is 0 the password
does not expire. If not 0, the value must be greater than or equal
to the value of the pwdMinAge.
( 1.3.6.1.4.1.42.2.27.8.1.3
NAME 'pwdMaxAge'
EQUALITY integerMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
SINGLE-VALUE )
5.2.4 pwdInHistory
This attribute specifies the maximum number of used passwords stored
in the pwdHistory attribute.
If this attribute is not present, or if the value is 0, used
passwords are not stored in the pwdHistory attribute and thus may be
reused.
( 1.3.6.1.4.1.42.2.27.8.1.4
NAME 'pwdInHistory'
EQUALITY integerMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
SINGLE-VALUE )
5.2.5 pwdCheckQuality
{TODO: Consider changing the syntax to OID. Each OID will list a
quality rule (like min len, # of special characters, etc). These
rules can be specified outside this document.}
{TODO: Note that even though this is meant to be a check that happens
during password modification, it may also be allowed to happen during
authN. This is useful for situations where the password is encrypted
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when modified, but decrypted when used to authN.}
This attribute indicates how the password quality will be verified
while being modified or added. If this attribute is not present, or
if the value is '0', quality checking will not be enforced. A value
of '1' indicates that the server will check the quality, and if the
server is unable to check it (due to a hashed password or other
reasons) it will be accepted. A value of '2' indicates that the
server will check the quality, and if the server is unable to verify
it, it will return an error refusing the password.
( 1.3.6.1.4.1.42.2.27.8.1.5
NAME 'pwdCheckQuality'
EQUALITY integerMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
SINGLE-VALUE )
5.2.6 pwdMinLength
When quality checking is enabled, this attribute holds the minimum
number of characters that must be used in a password. If this
attribute is not present, no minimum password length will be
enforced. If the server is unable to check the length (due to a
hashed password or otherwise), the server will, depending on the
value of the pwdCheckQuality attribute, either accept the password
without checking it ('0' or '1') or refuse it ('2').
( 1.3.6.1.4.1.42.2.27.8.1.6
NAME 'pwdMinLength'
EQUALITY integerMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
SINGLE-VALUE )
5.2.7 pwdExpireWarning
This attribute specifies the maximum number of seconds before a
password is due to expire that expiration warning messages will be
returned to an authenticating user.
If this attribute is not present, or if the value is 0 no warnings
will be returned. If not 0, the value must be smaller than the value
of the pwdMaxAge attribute.
( 1.3.6.1.4.1.42.2.27.8.1.7
NAME 'pwdExpireWarning'
EQUALITY integerMatch
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SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
SINGLE-VALUE )
5.2.8 pwdGraceAuthNLimit
This attribute specifies the number of times an expired password can
be used to authenticate. If this attribute is not present or if the
value is 0, authentication will fail.
( 1.3.6.1.4.1.42.2.27.8.1.8
NAME 'pwdGraceAuthNLimit'
EQUALITY integerMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
SINGLE-VALUE )
5.2.9 pwdLockout
This attribute indicates, when its value is "TRUE", that the password
may not be used to authenticate after a specified number of
consecutive failed bind attempts. The maximum number of consecutive
failed bind attempts is specified in pwdMaxFailure.
If this attribute is not present, or if the value is "FALSE", the
password may be used to authenticate when the number of failed bind
attempts has been reached.
( 1.3.6.1.4.1.42.2.27.8.1.9
NAME 'pwdLockout'
EQUALITY booleanMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.7
SINGLE-VALUE )
5.2.10 pwdLockoutDuration
This attribute holds the number of seconds that the password cannot
be used to authenticate due to too many failed bind attempts. If
this attribute is not present, or if the value is 0 the password
cannot be used to authenticate until reset by a password
administrator.
( 1.3.6.1.4.1.42.2.27.8.1.10
NAME 'pwdLockoutDuration'
EQUALITY integerMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
SINGLE-VALUE )
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5.2.11 pwdMaxFailure
This attribute specifies the number of consecutive failed bind
attempts after which the password may not be used to authenticate.
If this attribute is not present, or if the value is 0, this policy
is not checked, and the value of pwdLockout will be ignored.
( 1.3.6.1.4.1.42.2.27.8.1.11
NAME 'pwdMaxFailure'
EQUALITY integerMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
SINGLE-VALUE )
5.2.12 pwdFailureCountInterval
This attribute holds the number of seconds after which the password
failures are purged from the failure counter, even though no
successful authentication occurred.
If this attribute is not present, or if its value is 0, the failure
counter is only reset by a successful authentication.
( 1.3.6.1.4.1.42.2.27.8.1.12
NAME 'pwdFailureCountInterval'
EQUALITY integerMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
SINGLE-VALUE )
5.2.13 pwdMustChange
This attribute specifies with a value of "TRUE" that users must
change their passwords when they first bind to the directory after a
password is set or reset by a password administrator. If this
attribute is not present, or if the value is "FALSE", users are not
required to change their password upon binding after the password
administrator sets or resets the password. This attribute is not set
due to any actions specified by this document, it is typically set by
a password administrator after resetting a user's password.
( 1.3.6.1.4.1.42.2.27.8.1.13
NAME 'pwdMustChange'
EQUALITY booleanMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.7
SINGLE-VALUE )
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5.2.14 pwdAllowUserChange
This attribute indicates whether users can change their own
passwords, although the change operation is still subject to access
control. If this attribute is not present, a value of "TRUE" is
assumed. This attribute is intended to be used in the absense of an
access control mechanism.
( 1.3.6.1.4.1.42.2.27.8.1.14
NAME 'pwdAllowUserChange'
EQUALITY booleanMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.7
SINGLE-VALUE )
5.2.15 pwdSafeModify
This attribute specifies whether or not the existing password must be
sent along with the new password when being changed. If this
attribute is not present, a "FALSE" value is assumed.
( 1.3.6.1.4.1.42.2.27.8.1.15
NAME 'pwdSafeModify'
EQUALITY booleanMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.7
SINGLE-VALUE )
5.3 Attribute Types for Password Policy State Information
Password policy state information must be maintained for each user.
The information is located in each user entry as a set of operational
attributes. These operational attributes are: pwdChangedTime,
pwdAccountLockedTime, pwdFailureTime, pwdHistory, pwdGraceUseTime,
pwdReset, pwdPolicySubEntry.
5.3.1 Password Policy State Attribute Option
Since the password policy could apply to several attributes used to
store passwords, each of the above operational attributes must have
an option to specify which pwdAttribute it applies to. The password
policy option is defined as the following:
pwd-<passwordAttribute>
where passwordAttribute a string following the OID syntax
(1.3.6.1.4.1.1466.115.121.1.38). The attribute type descriptor
(short name) MUST be used.
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For example, if the pwdPolicy object has for pwdAttribute
"userPassword" then the pwdChangedTime operational attribute, in a
user entry, will be:
pwdChangedTime;pwd-userPassword: 20000103121520Z
This attribute option follows sub-typing semantics. If a client
requests a password policy state attribute to be returned in a search
operation, and does not specify an option, all subtypes of that
policy state attribute are returned.
5.3.2 pwdChangedTime
This attribute specifies the last time the entry's password was
changed. This is used by the password expiration policy. If this
attribute does not exist, the password will never expire.
( 1.3.6.1.4.1.42.2.27.8.1.16
NAME 'pwdChangedTime'
DESC 'The time the password was last changed'
EQUALITY generalizedTimeMatch
ORDERING generalizedTimeOrderingMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.24
SINGLE-VALUE
NO-USER-MODIFICATION
USAGE directoryOperation )
5.3.3 pwdAccountLockedTime
This attribute holds the time that the user's account was locked. A
locked account means that the password may no longer be used to
authenticate. A 000001010000Z value means that the account has been
locked permanently, and that only a password administrator can unlock
the account.
( 1.3.6.1.4.1.42.2.27.8.1.17
NAME 'pwdAccountLockedTime'
DESC 'The time an user account was locked'
EQUALITY generalizedTimeMatch
ORDERING generalizedTimeOrderingMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.24
SINGLE-VALUE
NO-USER-MODIFICATION
USAGE directoryOperation )
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5.3.4 pwdFailureTime
This attribute holds the timestamps of the consecutive authentication
failures.
( 1.3.6.1.4.1.42.2.27.8.1.19
NAME 'pwdFailureTime'
DESC 'The timestamps of the last consecutive authentication
failures'
EQUALITY generalizedTimeMatch
ORDERING generalizedTimeOrderingMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.24
NO-USER-MODIFICATION
USAGE directoryOperation )
5.3.5 pwdHistory
This attribute holds a history of previously used passwords. Values
of this attribute are transmitted in string format as given by the
following ABNF:
pwdHistory = time "#" syntaxOID "#" length "#" data
time = <generalizedTimeString as specified in 6.14
of [RFC2252]>
syntaxOID = numericoid ; the string representation of the
; dotted-decimal OID that defines the
; syntax used to store the password.
; numericoid is described in 4.1
; of [RFC2252].
length = numericstring ; the number of octets in data.
; numericstring is described in 4.1
; of [RFC2252].
data = <octets representing the password in the format
specified by syntaxOID>.
This format allows the server to store, and transmit a history of
passwords that have been used. In order for equality matching to
function properly, the time field needs to adhere to a consistent
format. For this purpose, the time field MUST be in GMT format.
( 1.3.6.1.4.1.42.2.27.8.1.20
NAME 'pwdHistory'
DESC 'The history of user s passwords'
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EQUALITY octetStringMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.40
NO-USER-MODIFICATION
USAGE directoryOperation )
5.3.6 pwdGraceUseTime
This attribute holds the timestamps of grace authentications after a
password has expired.
( 1.3.6.1.4.1.42.2.27.8.1.21
NAME 'pwdGraceUseTime'
DESC 'The timestamps of the grace authentication after the
password has expired'
EQUALITY generalizedTimeMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.24
NO-USER-MODIFICATION
USAGE directoryOperation )
5.3.7 pwdReset
This attribute holds a flag to indicate (when TRUE) that the password
has been updated by the password administrator and must be changed by
the user.
( 1.3.6.1.4.1.42.2.27.8.1.22
NAME 'pwdReset'
DESC 'The indication that the password has been reset'
EQUALITY booleanMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.7
SINGLE-VALUE
USAGE directoryOperation )
5.3.8 pwdPolicySubentry
This attribute points to the pwdPolicy subentry in effect for this
object.
( 1.3.6.1.4.1.42.2.27.8.1.23
NAME 'pwdPolicySubentry'
DESC 'The pwdPolicy subentry in effect for this object'
EQUALITY distinguishedNameMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.12
SINGLE-VALUE
NO-USER-MODIFICATION
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USAGE directoryOperation )
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6. Controls used for Password Policy
This section details the controls used while enforcing password
policy. A request control is defined that is sent by a client with a
request operation in order to elicit a response control. The
response control contains various warnings and errors associated with
password policy.
{TODO: add a note about advertisement and discovery}
6.1 Request Control
This control MAY be sent with any LDAP request message in order to
convey to the server that this client is aware of, and can process
the response control described in this document. When a server
receives this control, it will return the response control when
appropriate and with the proper data.
The controlType is 1.3.6.1.4.1.42.2.27.8.5.1 and the criticality may
be TRUE or FALSE. There is no controlValue.
6.2 Response Control
If the client has sent a passwordPolicyRequest control, the server
(when solicited by the inclusion of the request control) sends this
control with the following operation responses: bindResponse,
modifyResponse, addResponse, compareResponse and possibly
extendedResponse, to inform of various conditions, and MAY be sent
with other operations (in the case of the changeAfterReset error).
The controlType is 1.3.6.1.4.1.42.2.27.8.5.1 and the controlValue is
the BER encoding of the following type:
PasswordPolicyResponseValue ::= SEQUENCE {
warning [0] CHOICE {
timeBeforeExpiration [0] INTEGER (0 .. maxInt),
graceAuthNsRemaining [1] INTEGER (0 .. maxInt) } OPTIONAL,
error [1] ENUMERATED {
passwordExpired (0),
accountLocked (1),
changeAfterReset (2),
passwordModNotAllowed (3),
mustSupplyOldPassword (4),
insufficientPasswordQuality (5),
passwordTooShort (6),
passwordTooYoung (7),
passwordInHistory (8) } OPTIONAL }
The timeBeforeExpiration warning specifies the number of seconds
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before a password will expire. The graceAuthNsRemaining warning
specifies the remaining number of times a user will be allowed to
authenticate with an expired password. The passwordExpired error
signifies that the password has expired and must be reset. The
changeAfterReset error signifies that the password must be changed
before the user will be allowed to perform any operation other than
bind and modify. The passwordModNotAllowed error is set when a user
is restricted from changing her password. The
insufficientPasswordQuality error is set when a password doesn't pass
quality checking. The passwordTooYoung error is set if the age of
the password to be modified is not yet old enough.
Typically, only either a warning or an error will be encoded though
there may be exceptions. For example, if the user is required to
change a password after the password administrator set it, and the
password will expire in a short amount of time, the control may
include the timeBeforeExpiration warning and the changeAfterReset
error.
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7. Policy Decision Points
Following are a number of procedures used to make policy decisions.
These procedures are typically performed by the server while
processing an operation.
The following sections contain detailed instructions that refer to
attributes of the pwdPolicy object class. When doing so, the
attribute of the pwdPolicy object that governs the entry being
discussed is implied.
7.1 Locked Account Check
A status of true is returned to indicate that the account is locked
if any of these conditions are met:
o The value of the pwdAccountLockedTime attribute is 000001010000Z.
o The current time is less than the value of the
pwdAccountLockedTime attribute added to the value of the
pwdLockoutDuration.
Otherwise a status of false is returned.
7.2 Password Must be Changed Now Check
A status of true is returned to indicate that the account is locked
if all of these conditions are met:
The pwdMustChange attribute is set to TRUE.
The pwdReset attribute is set to TRUE.
Otherwise a status of false is returned.
7.3 Password Expiration Check
A status of true is returned indicating that the password has expired
if the current time minus the value of pwdChangedTime is greater than
the value of the pwdMaxAge.
Otherwise, a status of false is returned.
7.4 Remaining Grace AuthN Check
If the pwdGraceUseTime attribute is present, the number of values in
that attribute subtracted from the value of pwdGraceAuthNLimit is
returned. Otherwise zero is returned. A positive result specifies
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the number of remaining grace authentications.
7.5 Time Before Expiration Check
If the pwdExpireWarning attribute is not present a zero status is
returned. Otherwise the following steps are followed:
Subtract the time stored in pwdChangedTime from the current time to
arrive at the password's age. If the password's age is greater than
than the value of the pwdMaxAge attribute, a zero status is returned.
Subtract the value of the pwdExpireWarning attribute from the value
of the pwdMaxAge attribute to arrive at the warning age. If the
password's age is equal to or greater than the warning age, the value
of pwdMaxAge minus the password's age is returned.
7.6 Intruder Detection Check
A status of true indicating that an intruder has been detected is
returned if the following conditions are met:
The pwdLockout attribute is TRUE.
The number of values in the pwdFailureTime attribute that are
younger than pwdFailureCountInterval is greater or equal to the
pwdMaxFailure attribute.
Otherwise a status of false is returned.
While performing this check, values of pwdFailureTime that are old by
more than pwdFailureCountInterval are purged and not counted.
7.7 Password Too Young Check
A status of true indicating that not enough time has passed since the
password was last updated is returned if:
The value of pwdMinAge is non-zero and pwdChangedTime is present.
The value of pwdMinAge is greater than the current time minus the
value of pwdChangedTime.
Otherwise a false status is returned.
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8. Server Policy Enforcement Points
The server SHOULD enforce that the password attribute subject to a
password policy as defined in this document, contains one and only
one password value.
The scenarios in the following operations assume that the client has
attached a passwordPolicyRequest control to the request message of
the operation. In the event that the passwordPolicyRequest control
was not sent, no passwordPolicyResponse control is returned. All
other instructions remain the same.
For successfuly completed operations, unless otherwise stated, no
passwordPolicyResponse control is returned.
8.1 Password-based Authentication
This section contains the policy enforcement rules and policy data
updates used while validating a password. Operations that validate
passwords include, but are not limited to, the Bind operation where
the simple choice specifies a password, and the compare operation
where the attribute being compared holds a password. Note that while
the compare operation does not authenticate a user to the LDAP
server, it may be used by an external application for purposes of
authentication.
8.1.1 Fail if the account is locked
If the account is locked as specified in Section 7.1, the server
fails the operation with an appropriate resultCode (i.e.
invalidCredentials (49) in the case of a bind operation, compareFalse
(5) in the case of a compare operation, etc.). The server MAY set
the error: accountLocked (1) in the passwordPolicyResponse in the
controls field of the message.
8.1.2 Validated Password Procedures
If the validation operation indicates that the password validated,
these procedures are followed in order:
8.1.2.1 Policy state updates
Delete the pwdFailureTime and pwdAccountLockedTime attributes.
8.1.2.2 Password must be changed now
If the decision in Section 7.2 returns true, the server sends to the
client a response with an appropriate successful resultCode (i.e.
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success (0), compareTrue (6), etc.), and includes the
passwordPolicyResponse in the controls field of the bindResponse
message with the warning: changeAfterReset specified.
For bind, the server MUST then disallow all operations issued by this
user except modify password, bind, unbind, abandon and StartTLS
extended operation.
8.1.2.3 Expired password
If the password has expired as per Section 7.3, the server either
returns a success or failure based on the state of grace
authentications.
8.1.2.3.1 Remaining Grace Authentications
If there are remaining grace authentications as per Section 7.4, the
server adds a new value with the current time in pwdGraceUseTime.
Then it sends to the client a response with an appropriate successful
resultCode (i.e. success (0), compareTrue (6), etc.), and includes
the passwordPolicyResponse in the controls field of the response
message with the warning: graceAuthNsRemaining choice set to the
number of grace authentications left.
Implementor's note: The system time of the host machine may be more
granular than is needed to ensure unique values of this attribute.
It is recommended that a mechanism is used to ensure unique
generalized time values. The fractional seconds field may be used
for this purpose.
8.1.2.3.2 No Remaining Grace Authentications
If there are no remaining grace authentications, the server fails the
operation with an appropriate resultCode (invalidCredentials (49),
compareFalse (5), etc.), and includes the passwordPolicyResponse in
the controls field of the bindResponse message with the error:
passwordExpired (0) set.
8.1.2.4 Expiration Warning
If the result of Section 7.5 is a positive number, the server sends
to the client a response with an appropriate successful resultCode
(i.e. success (0), compareTrue (6), etc.), and includes the
passwordPolicyResponse in the controls field of the bindResponse
message with the warning: timeBeforeExiration set to the value as
described above. Otherwise, the server sends a successful response,
and omits the passwordPolicyResponse.
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8.1.2.5 AuthN Failed Procedures
If the authentication process indicates that the password failed
validation due to invalid credentials, these procedures are followed:
8.1.2.5.1 Policy state update
Add the current time as a value of the pwdFailureTime attribute.
Implementor's note: The system time of the host machine may be more
granular than is needed to ensure unique values of this attribute.
It is recommended that a mechanism is used to ensure unique
generalized time values. The fractional seconds field may be used
for this purpose.
8.1.2.5.2 Lock on intruder detection
If the check in Section 7.6 returns a true state, the server locks
the account by setting the value of the pwdAccountLockedTime
attribute to the current time. After locking the account, the server
fails the operation with an appropriate resultCode
(invalidCredentials (49), compareFalse (5), etc.), and includes the
passwordPolicyResponse in the controls field of the message with the
error: accountLocked (1).
8.2 Password Update Operations
Because the password is stored in an attribute, various operations
(like add and modify) may be used to create or update a password.
But some alternate mechanisms have been defined or may be defined,
such as the LDAP Password Modify Extended Operation [RFC3062].
While processing a password update, the server performs the following
steps:
8.2.1 Safe Modification
If pwdSafeModify is set to TRUE and if there is an existing password
value, the server ensures that the password update operation includes
the user's existing password.
When the LDAP modify operation is used to modify a password, this is
done by specifying both a delete action and an add or replace action,
where the delete action specifies the existing password, and the add
or replace action specifies the new password. Other password update
operations SHOULD employ a similar mechanism. Otherwise this policy
will fail.
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If the existing password is not specified, the server does not
process the operation and sends the appropriate response message to
the client with the resultCode: insufficientAccessRights (50), and
includes the passwordPolicyResponse in the controls field of the
response message with the error: mustSupplyOldPassword (4).
8.2.2 Change After Reset
If the decision in Section 7.2 returns true, the server ensures that
the password update operation contains no modifications other than
the modification of the password attribute. If other modifications
exist, the server sends a response message to the client with the
resultCode: insufficientAccessRights (50), and includes the
passwordPolicyResponse in the controls field of the response message
with the error: changeAfterReset (2).
8.2.3 Rights Check
Check to see whether the bound identity has sufficient rights to
update the password. If the bound identity is a user changing its
own password, this MAY be done by checking the pwdAllowUserChange
attribute or using an access control mechanism. The determination of
this is implementation specific. If the user is not allowed to
update her password, the server sends a response message to the
client with the resultCode: insufficientAccessRights (50), and
includes the passwordPolicyResponse in the controls field of the
response message with the error: passwordModNotAllowed (3).
8.2.4 Too Early to Update
If the check in Section 7.7 results in a true status The server sends
a response message to the client with the resultCode:
constraintViolation (19), and includes the passwordPolicyResponse in
the controls field of the response message with the error:
passwordTooYoung (7).
8.2.5 Password Quality
Check the value of the pwdCheckQuality attribute. If the value is
non-zero, the server:
o Ensure that the password meets the quality criteria enforced by
the server. This enforcement is implementation specific.
If the server is unable to check the quality (due to a hashed
password or otherwise), the value of pwdCheckQuality is evaluated.
If the value is 1, operation continues. If the value is 2, the
server sends a response message to the client with the resultCode:
constraintViolation (19), and includes the passwordPolicyResponse
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in the controls field of the response message with the error:
insufficientPasswordQuality (5).
If the server is able to check the password quality, and the check
fails, the server sends a response message to the client with the
resultCode: constraintViolation (19), and includes the
passwordPolicyResponse in the controls field of the response
message with the error: insufficientPasswordQuality (5).
o checks the value of the pwdMinLength attribute. If the value is
non-zero, it ensures that the new password is of at least the
minimum length.
If the server is unable to check the length (due to a hashed
password or otherwise), the value of pwdCheckQuality is evaluated.
If the value is 1, operation continues. If the value is 2, the
server sends a response message to the client with the resultCode:
constraintViolation (19), and includes the passwordPolicyResponse
in the controls field of the response message with the error:
passwordTooShort (6).
If the server is able to check the password length, and the check
fails, the server sends a response message to the client with the
resultCode: constraintViolation (19), and includes the
passwordPolicyResponse in the controls field of the response
message with the error: passwordTooShort (6).
8.2.6 Invalid Reuse
If pwdInHistory is present and its value is non-zero, the server
checks whether this password exists in the entry's pwdHistory
attribute or in the current password attribute. If the password does
exist in the pwdHistory attribute or in the current password
attribute, the server sends a response message to the client with the
resultCode: constraintViolation (19), and includes the
passwordPolicyResponse in the controls field of the response message
with the error: passwordInHistory (8).
8.2.7 Policy State Updates
If the steps have completed without causing an error condition, the
server performs the following steps in order to update the necessary
password policy state attributes:
If the value of either pwdMaxAge or pwdMinAge is non-zero, the server
updates the pwdChangedTime attribute on the entry to the current
time.
If the value of pwdInHistory is non-zero, the server adds the
previous password (if one existed) to the pwdHistory attribute. If
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the number of attributes held in the pwdHistory attribute exceeds the
value of pwdInHistory, the server removes the oldest excess
passwords.
If the value the pwdMustChange is TRUE and the modification is
performed by a password administrator, then the pwdReset attribute is
set to TRUE. Otherwise, the pwdReset is removed from the user's
entry if it exists.
The pwdFailureTime and pwdGraceUseTime attributes is removed from the
user's entry if they exist.
8.3 Other Operations
For operations other than bind, password update, unbind, abandon or
StartTLS, if the decision in Section 7.2 returns true, the server
sends a response message to the client with the resultCode:
insufficientAccessRights (50), and includes the
passwordPolicyResponse in the controls field of the response message
with the error: changeAfterReset (2).
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9. Client Policy Enforcement Points
These sections illustrate possible scenarios for each LDAP operation
and define the types of responses that identify those scenarios.
The scenarios in the following operations assume that the client
attached a passwordPolicyRequest control to the request message of
the operation, and thus may receive a passwordPolicyResponse control
in the response message. In the event that the passwordPolicyRequest
control was not sent, no passwordPolicyResponse control is returned.
All other instructions remain the same.
9.1 Bind Operation
For every bind response received, the client checks the resultCode of
the bindResponse and checks for a passwordPolicyResponse control to
determine if any of the following conditions are true and MAY prompt
the user accordingly.
o bindResponse.resultCode = insufficientAccessRights (50),
passwordPolicyResponse.error = accountLocked (1): The password
failure limit has been reached and the account is locked. The
user needs to retry later or contact the password administrator to
reset the password.
o bindResponse.resultCode = success (0),
passwordPolicyResponse.error = changeAfterReset (2): The user is
binding for the first time after the password administrator set
the password. In this scenario, the client SHOULD prompt the user
to change his password immediately.
o bindResponse.resultCode = success (0),
passwordPolicyResponse.warning = graceAuthNsRemaining: The
password has expired but there are remaining grace
authentications. The user needs to change it.
o bindResponse.resultCode = invalidCredentials (49),
passwordPolicyResponse.error = passwordExpired (0): The password
has expired and there are no more grace authentications. The user
contacts the password administrator in order to have its password
reset.
o bindResponse.resultCode = success (0),
passwordPolicyResponse.warning = timeBeforeExpiration: The user's
password will expire in n number of seconds.
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9.2 Modify Operations
9.2.1 Modify Request
If the application or client encrypts the password prior to sending
it in a password modification operation (whether done through
modifyRequest or another password modification mechanism), it SHOULD
check the values of the pwdMinLength, and pwdCheckQuality attributes
and SHOULD enforce these policies.
9.2.2 Modify Response
If the modifyRequest operation was used to change the password, or if
another mechanism is used --such as an extendedRequest-- the
modifyResponse or other appropriate response MAY contain information
pertinent to password policy. The client checks the resultCode of
the response and checks for a passwordPolicyResponse control to
determine if any of the following conditions are true and optionally
notify the user of the condition.
o <pwdModResponse>.resultCode = insufficientAccessRights (50),
passwordPolicyResponse.error = mustSupplyOldPassword (4): The user
attempted to change her password without specifying the old
password but the password policy requires this.
o <pwdModResponse>.resultCode = insufficientAccessRights (50),
passwordPolicyResponse.error = changeAfterReset (2): The user must
change her password before submitting any other LDAP requests.
o <pwdModResponse>.resultCode = insufficientAccessRights (50),
passwordPolicyResponse.error = passwordModNotAllowed (3): The user
doesn't have sufficient rights to change his password.
o <pwdModResponse>.resultCode = constraintViolation (19),
passwordPolicyResponse.error = passwordTooYoung (7): It is too
soon after the last password modification to change the password.
o <pwdModResponse>.resultCode = constraintViolation (19),
passwordPolicyResponse.error = insufficientPasswordQuality (5):
The password failed quality checking.
o <pwdModResponse>.resultCode = constraintViolation (19),
passwordPolicyResponse.error = passwordTooShort (6): The length of
the password is too short.
o <pwdModResponse>.resultCode = constraintViolation (19),
passwordPolicyResponse.error = passwordInHistory (8): The password
has already been used; the user must choose a different one.
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9.3 Add Operation
If a password is specified in an addRequest, the client checks the
resultCode of the addResponse and checks for a passwordPolicyResponse
control to determine if any of the following conditions are true and
may prompt the user accordingly.
o addResponse.resultCode = insufficientAccessRights (50),
passwordPolicyResponse.error = passwordModNotAllowed (3): The user
doesn't have sufficient rights to add this password.
o addResponse.resultCode = constraintViolation (19),
passwordPolicyResponse.error = insufficientPasswordQuality (5):
The password failed quality checking.
o addResponse.resultCode = constraintViolation (19),
passwordPolicyResponse.error = passwordTooShort (6): The length of
the password is too short.
9.4 Compare Operation
When a compare operation is used to compare a password, the client
checks the resultCode of the compareResponse and checks for a
passwordPolicyResponse to determine if any of the following
conditions are true and MAY prompt the user accordingly. These
conditions assume that the result of the comparison was true.
o compareResponse.resultCode = compareFalse (5),
passwordPolicyResponse.error = accountLocked (1): The password
failure limit has been reached and the account is locked. The
user needs to retry later or contact the password administrator to
reset the password.
o compareResponse.resultCode = compareTrue (6),
passwordPolicyResponse.warning = graceAuthNsRemaining: The
password has expired but there are remaining grace
authentications. The user needs to change it.
o compareResponse.resultCode = compareFalse (5),
passwordPolicyResponse.error = passwordExpired (0): The password
has expired and there are no more grace authentications. The user
must contact the password administrator to reset the password.
o compareResponse.resultCode = compareTrue (6),
passwordPolicyResponse.warning = timeBeforeExpiration: The user's
password will expire in n number of seconds.
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9.5 Other Operations
For operations other than bind, unbind, abandon or StartTLS, the
client checks the following result code and control to determine if
the user needs to change the password immediately.
o <Response>.resultCode = insufficientAccessRights (50),
passwordPolicyResponse.error = : changeAfterReset (2)
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10. Administration of the Password Policy
{TODO: Need to define an administrativeRole (need OID). Need to
describe whether pwdPolicy admin areas can overlap}
A password policy is defined for a particular subtree of the DIT by
adding to an LDAP subentry whose immediate superior is the root of
the subtree, the pwdPolicy auxiliary object class. The scope of the
password policy is defined by the SubtreeSpecification attribute of
the LDAP subentry as specified in [RFC3672].
It is possible to define password policies for different password
attributes within the same pwdPolicy entry, by specifying multiple
values of the pwdAttribute. But password policies could also be in
separate sub entries as long as they are contained under the same
LDAP subentry.
Modifying the password policy MUST NOT result in any change in users'
entries to which the policy applies.
It SHOULD be possible to overwrite the password policy for one user
by defining a new policy in a subentry of the user entry.
Each object that is controlled by password policy advertises the
subentry that is being used to control its policy in its
pwdPolicySubentry attribute. Clients wishing to examine or manage
password policy for an object may interrogate the pwdPolicySubentry
for that object in order to arrive at the proper pwdPolicy subentry.
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11. Password Policy and Replication
{TODO: This section needs to be changed to highlight the pitfals of
replication, sugest some implementation choices to overcome those
pitfals, but remove prescriptive language relating to the update of
state information}
The pwdPolicy object defines the password policy for a portion of the
DIT and MUST be replicated on all the replicas of this subtree, as
any subentry would be, in order to have a consistent policy among all
replicated servers.
The elements of the password policy that are related to the users are
stored in the entry themselves as operational attributes. As these
attributes are subject to modifications even on a read-only replica,
replicating them must be carefully considered.
The pwdChangedTime attribute MUST be replicated on all replicas, to
allow expiration of the password.
The pwdReset attribute MUST be replicated on all replicas, to deny
access to operations other than bind and modify password.
The pwdHistory attribute MUST be replicated to writable replicas. It
doesn't have to be replicated to a read-only replica, since the
password will never be directly modified on this server.
The pwdAccountLockedTime, pwdFailureTime and pwdGraceUseTime
attributes MUST be replicated to writable replicas, making the
password policy global for all servers. When the user entry is
replicated to a read-only replica, these attributes SHOULD NOT be
replicated. This means that the number of failures, of grace
authentications and the locking will take place on each replicated
server. For example, the effective number of failed attempts on a
user password will be N x M (where N is the number of servers and M
the value of pwdMaxFailure attribute). Replicating these attributes
to a read-only replica MAY reduce the number of tries globally but
MAY also introduce some inconstancies in the way the password policy
is applied.
Servers participating in a loosely consistent multi-master
replication agreement SHOULD employ a mechanism which ensures
uniqueness of values when populating the attributes pwdFailureTime
and pwdGraceUseTime. The method of achieving this is a local matter
and may consist of using a single authoritative source for the
generation of unique time values, or may consist of the use of the
fractional seconds part to hold a replica identifier.
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12. Security Considerations
This document defines a set of rules to implement in an LDAP server,
in order to mitigate some of the security risks associated with the
use of passwords and to make it difficult for password cracking
programs to break into directories.
Authentication with a password MUST follow the recommendations made
in [RFC2829].
Modifications of passwords SHOULD only occur when the connection is
protected with confidentiality and secure authentication.
Access controls SHOULD be used to restrict access to the password
policy attributes. The attributes defined to maintain the password
policy state information SHOULD only be modifiable by the password
administrator or higher authority. The pwdHistory attribute MUST be
subject to the same level of access control as the attrbute holding
the password.
As it is possible to define a password policy for one specific user
by adding a subentry immediately under the user's entry, Access
Controls SHOULD be used to restrict the use of the pwdPolicy object
class or the LDAP subentry object class.
When the intruder detection password policy is enforced, the LDAP
directory is subject to a denial of service attack. A malicious user
could deliberately lock out one specific user's account (or all of
them) by sending bind requests with wrong passwords. There is no way
to protect against this kind of attack. The LDAP directory server
SHOULD log as much information as it can (such as client IP address)
whenever an account is locked, in order to be able to identify the
origin of the attack. Denying anonymous access to the LDAP directory
is also a way to restrict this kind of attack.
Returning certain status codes (such as passwordPolicyResponse.error
= accountLocked) allows a denial of service attacker to know that it
has successfully denied service to an account. Servers SHOULD
implement additional checks which return the same status when it is
sensed that some number of failed authentication requests has occured
on a single connection, or from a client address. Server
implementors are encouraged to invent other checks similar to this in
order to thwart this type of DoS attack.
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13. IANA Considerations
<<<TBD>>>
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14. Acknowledgement
This document is based in part on prior work done by Valerie Chu from
Netscape Communications Corp, published as
draft-vchu-ldap-pwd-policy-00.txt (December 1998). Prasanta Behera
participated in early revisions of this document.
15. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2195] Klensin, J., Catoe, R., and P. Krumviede, "IMAP/POP
AUTHorize Extension for Simple Challenge/Response",
RFC 2195, September 1997.
[RFC2222] Myers, J., "Simple Authentication and Security Layer
(SASL)", RFC 2222, October 1997.
[RFC2251] Wahl, M., Howes, T., and S. Kille, "Lightweight Directory
Access Protocol (v3)", RFC 2251, December 1997.
[RFC2252] Wahl, M., Coulbeck, A., Howes, T., and S. Kille,
"Lightweight Directory Access Protocol (v3): Attribute
Syntax Definitions", RFC 2252, December 1997.
[RFC2829] Wahl, M., Alvestrand, H., Hodges, J., and R. Morgan,
"Authentication Methods for LDAP", RFC 2829, May 2000.
[RFC2831] Leach, P. and C. Newman, "Using Digest Authentication as a
SASL Mechanism", RFC 2831, May 2000.
[RFC3062] Zeilenga, K., "LDAP Password Modify Extended Operation",
RFC 3062, February 2001.
[RFC3383] Zeilenga, K., "Internet Assigned Numbers Authority (IANA)
Considerations for the Lightweight Directory Access
Protocol (LDAP)", BCP 64, RFC 3383, September 2002.
[RFC3672] Zeilenga, K., "Subentries in the Lightweight Directory
Access Protocol (LDAP)", RFC 3672, December 2003.
[X680] International Telecommunications Union, "Abstract Syntax
Notation One (ASN.1): Specification of basic notation",
ITU-T Recommendation X.680, July 2002.
[X690] International Telecommunications Union, "Information
Technology - ASN.1 encoding rules: Specification of Basic
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Encoding Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER)", ITU-T Recommendation
X.690, July 2002.
Authors' Addresses
Jim Sermersheim
Novell, Inc
1800 South Novell Place
Provo, Utah 84606
USA
Phone: +1 801 861-3088
Email: jimse@novell.com
Ludovic Poitou
Sun Microsystems
180, Avenue de l'Europe
Zirst de Montbonnot, 38334 Saint Ismier cedex
France
Phone: +33 476 188 212
Email: ludovic.poitou@sun.com
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