CVE-2026-40205 Auth bypass in OX Dovecot CE
Attackers with partial OAuth2 scopes can bypass authorization checks in remote token validation, gaining unauthorized access to Dovecot services.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-40205?
CVE-2026-40205 is a medium-severity authentication bypass vulnerability in Open-Xchange GmbH OX Dovecot CE, published on 28 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
An attacker that holds an OAuth2 token granting only part of the required scopes can authenticate, because when more than one scope is required in the configuration, the remote token validation paths accept a token that carries only one of them, while the local token validation path correctly requires all of them. The configured authorization policy is not enforced, so a token that was granted only part of the required permissions is accepted where it should have been rejected. Use local token validation where tokens can be validated locally. Update to non-vulnerable version. No publicly available exploits are known.
Weakness: CWE-287
Which versions are affected by CVE-2026-40205?
How do I fix CVE-2026-40205?
Upgrade to a fixed version.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-40205 being exploited?
There is no known exploitation of CVE-2026-40205 in the wild and no public exploit code.
Sources
Also known as ALPINE-CVE-2026-40205, AZL-98307, DEBIAN-CVE-2026-40205, GHSA-8rjh-g9p7-rx87, UBUNTU-CVE-2026-40205.