GHSA-vq6g-g6c7-5f2j

### Impact

The SAML backend accepted SAML responses on the Assertion Consumer Service endpoint without verifying that they matched a previously issued `AuthnRequest`.

Applications using SAML account association could allow an attacker with a valid account on a trusted IdP to link the attacker's SAML identity to a logged-in victim's local account. The attacker could then authenticate through SAML and gain access to the victim's account.

The issue affects applications using the SAML backend together with authenticated account association.

### Patches

The issue has been fixed by validating SAML responses against stored `AuthnRequest` IDs.

Users should upgrade to a patched version.

Fix:

* https://github.com/python-social-auth/social-core/pull/1794

### Workarounds

Applications that cannot upgrade immediately should disable SAML account association for already authenticated users.

If SAML login is not required, the SAML backend can also be disabled by removing it from `SOCIAL_AUTH_AUTHENTICATION_BACKENDS`.

There is no complete workaround while continuing to allow vulnerable SAML account association.

### Credits

Reported through GitHub private vulnerability reporting by Liyi Zhou, Ziyue Wang, Strick, Maurice, and Chenchen Yu from the University of Sydney security research team.

Reporter references:

* https://lzhou1110.github.io/ * https://zyy0530.github.io/ * https://str1ckl4nd.github.io/ * https://maurice.busystar.org/ * https://7thparkk.github.io/