Synapse has improper checks for deactivated users during login

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;