CVE-2026-27859 Denial of service in OX Dovecot Pro
An attacker can cause excessive CPU consumption in the LMTP mail delivery process by sending a mail message with excessive RFC 2231 MIME parameters.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-27859?
CVE-2026-27859 is a medium-severity denial of service vulnerability in Dovecot Dovecot, published on 27 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
A mail message containing excessive amount of RFC 2231 MIME parameters causes LMTP to use too much CPU. A suitably formatted mail message causes mail delivery process to consume large amounts of CPU time. Use MTA capabilities to limit RFC 2231 MIME parameters in mail messages, or upgrade to fixed version where the processing is limited. No publicly available exploits are known.
Weakness: CWE-400
Which versions are affected by CVE-2026-27859?
It affects 2 products.
Products include Dovecot Dovecot, Open-Xchange Dovecot.
How do I fix CVE-2026-27859?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-27859 being exploited?
There is no known exploitation of CVE-2026-27859 in the wild and no public exploit code.
Other vulnerabilities in Dovecot Dovecot
Sources
Also known as ALPINE-CVE-2026-27859, AZL-81713, DEBIAN-CVE-2026-27859, GHSA-3rfp-26pp-jqjf, UBUNTU-CVE-2026-27859.