Improper checks for deactivated users during login in synapse

Vulnerability Description

Synapse is a Matrix protocol homeserver written in Python with the Twisted framework. In affected versions it may be possible for a deactivated user to login when using uncommon configurations. This only applies if any of the following are true: 1. JSON Web Tokens are enabled for login via the `jwt_config.enabled` configuration setting. 2. 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. If not using JSON Web Tokens, ensure that deactivated users do not have a password set. This issue has been addressed in version 1.85.0. Users are advised to upgrade.

References

• https://github.com/matrix-org/synapse/security/advisories/GHSA-26c5-ppr8-f33p
• https://github.com/matrix-org/synapse/pull/15624
• https://github.com/matrix-org/synapse/pull/15634
• https://matrix-org.github.io/synapse/latest/admin_api/user_admin_api.html#create-or-modify-account
• https://matrix-org.github.io/synapse/latest/jwt.html
• https://matrix-org.github.io/synapse/latest/usage/configuration/config_documentation.html#password_config
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/X6DH5A5YEB5LRIPP32OUW25FCGZFCZU2/