CVE-2026-27855: Medium severity Dovecot dovecot vulnerability
Dovecot OTP authentication is vulnerable to replay attack under specific conditions. If auth cache is enabled, and username is altered in passdb, then OTP credentials can be cached so that same OTP reply is valid. An attacker able to observe an OTP exchange is able to log in as the user. If authentication happens over unsecure connection, switch to SCRAM protocol. Alternatively ensure the communcations are secured, and if possible switch to OAUTH2 or SCRAM. No publicly available exploits are known.
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-27855?
CVE-2026-27855 is considered a medium severity vulnerability due to the risk of replay attacks.
How do I fix CVE-2026-27855?
To fix CVE-2026-27855, ensure that the auth cache is disabled or properly configured to mitigate the replay attack risk.
What systems are affected by CVE-2026-27855?
CVE-2026-27855 affects Dovecot installations that have OTP authentication with auth cache enabled.
What is a replay attack in the context of CVE-2026-27855?
A replay attack in CVE-2026-27855 occurs when an attacker reuses a valid OTP to gain unauthorized access if the OTP is cached.
How can an attacker exploit CVE-2026-27855?
An attacker can exploit CVE-2026-27855 by observing an OTP exchange and later using the cached OTP for authentication.