Impact

It may be possible for a deactivated user to login when using uncommon configurations.

This only applies if any of the following are true:

- JSON Web Tokens are enabled for login via the jwt_config.enabled configuration setting
- The local password database is enabled via the password_config.enabled and password_config.localdb_enabled configuration settings and a user's password is updated via an admin API after a user is deactivated.

Note that the local password database is enabled by default, but it is uncommon to set a user's password after they've been deactivated.

Installations that are configured to only allow login via Single Sign-On (SSO) via CAS, SAML or OpenID Connect (OIDC); or via an external password provider (e.g. LDAP) are not affected.


Patches

- If using JSON Web Token logins: #15624
- For other users: #15634

Workarounds

If not using JSON Web Tokens, ensure that deactivated users do not have a password set. This list of users can be queried from PostgreSQL:

> SELECT name FROM users WHERE password_hash IS NOT NULL AND deactivated = 1;

reference:

https://github.com/matrix-org/synapse/releases/tag/v1.85.0
https://github.com/matrix-org/synapse/security/advisories/GHSA-26c5-ppr8-f33p