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 NameID
s even if it is not properly configured to generate them based on the specifics of the deployment.
Persistent NameID
s 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:
NameID
.saml:PersistentNameID
authentication processing filter is configured (neither for the whole IdP, nor for a given SP).simplesaml.nameidattribute
configuration option is set (neither for the whole IdP, nor for a given SP).userid.attribute
configuration option is set and the users don't have an eduPersonPrincipalName
attribute in the users backend, oruserid.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 NameID
s, 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:
null
value.All SimpleSAMLphp versions between 1.7.0 and 1.14.10, inclusive.
Those identity providers affected by this bug and misconfigured as previously described could be issuing SAML assertions with common NameID
s for all or a subset of their users. If a service provider uses those NameID
s 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.
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.
{ "nvd_published_at": null, "cwe_ids": [ "CWE-384" ], "severity": "CRITICAL", "github_reviewed": true, "github_reviewed_at": "2020-01-24T21:24:46Z" }