CVE-2026-27855

Description

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.

How to fix CVE-2026-27855

To remediate CVE-2026-27855, upgrade the affected package to a fixed version below.

• —upgrade to 2.4.3-r0 or later
• —upgrade to 1:2.3.13+dfsg1-2+deb11u3 or later

Is CVE-2026-27855 being exploited?

Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.

Affected packages (2)

• from 0, < 2.4.3-r0
• from 0, < 1:2.3.13+dfsg1-2+deb11u3

CVSS scores

References (2)

• ADVISORYsecurity.alpinelinux.org/vuln/CVE-2026-27855
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2026-27855