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Incorrect persistent NameID generation in SimpleSAMLphp

Critical severity GitHub Reviewed Published Jun 5, 2019 in simplesamlphp/simplesamlphp • Updated Feb 7, 2024

Package

composer simplesamlphp/simplesamlphp (Composer)

Affected versions

>= 1.7.0, < 1.14.11

Patched versions

1.14.11

Description

Background

When a SimpleSAMLphp Identity Provider is misconfigured, a bug in the software when trying to build a persistent NameID to univocally identify the authenticating subject could cause different users to get the same identifier generated, depending on the attributes available for them right after authentication.

Please note that even though this is possible thanks to a bug, an IdP must be misconfigured to release persistent NameIDs even if it is not properly configured to generate them based on the specifics of the deployment.

Description

Persistent NameIDs will typically be sent as part of the Subject element of a SAML assertion, or as the contents of the eduPersonTargetedID attribute. Here is an example of such a NameID:

<NameID Format=“urn:oasis:names:tc:SAML:2.0:nameid-format:persistent“>
    zbonsm0Yn9Gnw14uQEEPr6AO7d+IvxwCQN3t+o24jYs=
</NameID>

Some service providers will use this information to identify a user across sessions because a persistent NameID will never change for a given user. This could lead to different users accessing the same account in those service providers.

In order to be affected by this issue, the following circumstances must concur:

  • SimpleSAMLphp acts as an identity provider.
  • The service provider asking for authentication requests a persistent NameID.
  • No saml:PersistentNameID authentication processing filter is configured (neither for the whole IdP, nor for a given SP).
  • No simplesaml.nameidattribute configuration option is set (neither for the whole IdP, nor for a given SP).
  • One of the following alternatives:
    • No userid.attribute configuration option is set and the users don't have an eduPersonPrincipalName attribute in the users backend, or
    • the userid.attribute configuration option is set to an empty or missing attribute.

If all these requirements are met, the SimpleSAML_Auth_ProcessingChain class will try to keep a unique user identifier in the state array (addUserID() method). Bear in mind that this code is executed before all the authentication processing filters configured, meaning that only those attributes retrieved for the user during initial authentication will be available. If no userid.attribute configuration option is set, the default eduPersonPrincipalName will then be used. However, since it is missing, no identifier will be kept. Alternatively, if userid.attribute is set to a missing or empty attribute, the addUserID() method will abort trying to register an identifier.

After executing all authentication processing filters, SimpleSAMLphp will build a SAML assertion. If the service provider requests persistent NameIDs, SimpleSAMLphp will attempt to generate one given that none is already available (because the saml:PersistentNameID filter was not used). At this point, the code will look for the simplesaml.nameidattribute configuration option in either the local IdP metadata or in the remote SP metadata. If none of them are configured, it will default to the unique user identifier previously registered by SimpleSAML_Auth_ProcessingChain. If no identifier was kept there, the code will log an error message:

Unable to generate NameID. Check the userid.attribute option.

However, instead of aborting the NameID generation at that point, it will go on and use a value missing from the state array as the source for the computation, meaning the null type will be used. Hence, all users connecting to a given service provider will get the same NameID generated, because all the input parameters will be the same:

  • The SP's entity identifier.
  • The IdP's entity identifier.
  • The null value.
  • The common secret salt from the main configuration.

Affected versions

All SimpleSAMLphp versions between 1.7.0 and 1.14.10, inclusive.

Impact

Those identity providers affected by this bug and misconfigured as previously described could be issuing SAML assertions with common NameIDs for all or a subset of their users. If a service provider uses those NameIDs to identify the users of the affected IdP, all the users will be associated with the same user account at the service provider, causing all sorts of potential security issues like information disclosure or unauthorized access.

While we can consider this unlikely to happen, some cases have been already observed. In particular, some identity providers using default configurations and consuming metadata automatically (i.e. using the metarefresh module) while using a user backend like Active Directory that does not populate eduPersonPrincipalName are particularly sensitive to this issue.

Resolution

Upgrade to the latest version.

Configure a saml:PersistentNameID authentication processing filter according to your needs. Remember to check that the attribute used as the source for the NameID is present at the moment the saml:PersistentNameID filter is executed. The attribute used must be unique per user, and must not change over time.

References

@jaimeperez jaimeperez published to simplesamlphp/simplesamlphp Jun 5, 2019
Reviewed Jan 24, 2020
Published to the GitHub Advisory Database Jan 24, 2020
Last updated Feb 7, 2024

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS score

0.394%
(74th percentile)

Weaknesses

CVE ID

CVE-2017-12873

GHSA ID

GHSA-gp2m-7cfp-h6gf

Source code

No known source code
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