Impact

The Vend OAuth2 backend used only the numeric Vend user_id as the social-auth UID.

When multiple Vend shops authenticate through the same application, users from different shops with the same internal Vend user ID could collide in the social-auth association table. A user from one shop could then be authenticated as the local account previously associated with the same numeric user ID from another shop.

The issue affects applications using the Vend OAuth2 backend with more than one Vend shop.

Patches

The issue has been fixed by scoping Vend social-auth UIDs by shop.

Users should upgrade to a patched version.

Fix:

• #1795

Workarounds

Applications that cannot upgrade immediately should restrict the Vend OAuth2 backend to a single trusted Vend shop.

If Vend authentication is not required, the Vend backend can also be disabled by removing it from SOCIAL_AUTH_AUTHENTICATION_BACKENDS.

There is no complete workaround while continuing to allow authentication from multiple Vend shops with the vulnerable backend.

References

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/