What is CVE-2026-27859?

CVE-2026-27859 is a medium-severity vulnerability in Dovecot, classified under Uncontrolled Resource Consumption. CVSS score: 5.3/10. Published 2026-03-27.

How severe is CVE-2026-27859?

Medium severity. CVSS v3 base score is 5.3 out of 10.

Resource exhaustion in Dovecot

CVE-2026-27859

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.

Vulnerability class: DoS (Denial of Service)

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

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.

EPSS exploit prediction

EPSS: 0.004 (33.3th percentile), scored 2026-10-23.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 33rd percentile — 33.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: +0.000

Affected products

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

Weakness classification (CWE)

CWE-400 — Uncontrolled Resource Consumption

References

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

Frequently asked questions

What is CVE-2026-27859?: CVE-2026-27859 is a medium-severity vulnerability in Dovecot, classified under Uncontrolled Resource Consumption. CVSS score: 5.3/10. Published 2026-03-27.
How severe is CVE-2026-27859?: Medium severity. CVSS v3 base score is 5.3 out of 10.