Vulnerability · Published Mar 27, 2026 · Assigned by OX
CVE-2026-27855
Medium 6.8
In plain English
A medium-severity security flaw in OX Dovecot Pro from Open-Xchange GmbH. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 25% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.23 | dovecot | 2.4.3-r0 | ALPINE-CVE-2026-27855 |
| Alpine:v3.24 | dovecot | 2.4.3-r0 | ALPINE-CVE-2026-27855 |
| Debian:12 | dovecot | 1:2.3.19.1+dfsg1-2.1+deb12u2 | DEBIAN-CVE-2026-27855 |
| Debian:13 | dovecot | 1:2.4.1+dfsg1-6+deb13u4 | DEBIAN-CVE-2026-27855 |
| Debian:14 | dovecot | 1:2.4.3+dfsg1-1 | DEBIAN-CVE-2026-27855 |
| Ubuntu:22.04:LTS | dovecot | 1:2.3.16+dfsg1-3ubuntu2.7 | UBUNTU-CVE-2026-27855 |
| Ubuntu:24.04:LTS | dovecot | 1:2.3.21+dfsg1-2ubuntu6.3 | UBUNTU-CVE-2026-27855 |
| Ubuntu:25.10 | dovecot | 1:2.4.1+dfsg1-5ubuntu4.1 | UBUNTU-CVE-2026-27855 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Open-Xchange GmbH | OX Dovecot Pro | 0 – through 2.3.0 |
Weakness: CWE-294 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N