CVE-2026-40013: Open-Xchange GmbH Ox Dovecot CE

Medium severity, CVSS 4.3. EPSS: 0.9% chance of exploitation in the next 30 days.

An attacker that has valid credentials can submit a Sieve script containing an extreme numeric literal, which causes an out-of-bounds write when the ManageSieve service compiles the script. This causes memory corruption and an observed crash of the ManageSieve process, resulting in denial of service for script management. This might be able to be used for remote code execution. Disable the ManageSieve service if users do not need remote Sieve script management. Update to non-vulnerable version. No publicly available exploits are known.

Affected products

• Open-Xchange GmbH Ox Dovecot CE: from 2.3.0, before 2.4.5 (fixed in 2.4.5)
• Open-Xchange GmbH Ox Dovecot Pro: from 2.3.0, before 2.3.22.2 (fixed in 2.3.22.2); from 3.0.0, before 3.0.7 (fixed in 3.0.7); from 3.1.0, before 3.1.6 (fixed in 3.1.6)

Published 2026-08-28. Last modified 2026-09-03.