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;

References

• GHSA-26c5-ppr8-f33p
• matrix-org/synapse#12274
• matrix-org/synapse#15624
• matrix-org/synapse#15634
• https://github.com/matrix-org/synapse/releases/tag/v1.85.0
• https://nvd.nist.gov/vuln/detail/CVE-2023-32682
• 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://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2023-84.yaml
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/X6DH5A5YEB5LRIPP32OUW25FCGZFCZU2/