What is CVE-2026-27855?

CVE-2026-27855 is a medium-severity vulnerability in Dovecot, classified under Authentication Bypass by Capture-replay. CVSS score: 6.8/10. Published 2026-03-27.

How severe is CVE-2026-27855?

Medium severity. CVSS v3 base score is 6.8 out of 10.

Vulnerability in Dovecot

CVE-2026-27855

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.

Published 2026-03-27 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.8 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N.

EPSS exploit prediction

EPSS: 0.004 (31.4th percentile), scored 2026-10-23.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 31st percentile — 31.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.004 · change: +0.001

Affected products

Dovecot
Open-Xchange Dovecot
Open-Xchange Gmbh Ox Dovecot Pro — versions 0

Weakness classification (CWE)

CWE-294 — Authentication Bypass by Capture-replay

References

documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2… (vendor-advisory, Vendor Advisory)

Frequently asked questions

What is CVE-2026-27855?: CVE-2026-27855 is a medium-severity vulnerability in Dovecot, classified under Authentication Bypass by Capture-replay. CVSS score: 6.8/10. Published 2026-03-27.
How severe is CVE-2026-27855?: Medium severity. CVSS v3 base score is 6.8 out of 10.