Resource exhaustion in Dovecot

CVE-2026-27857

Sending "NOOP (((...)))" command with 4000 parenthesis open+close results in ~1MB extra memory usage. Longer commands will result in client disconnection. This 1 MB can be left allocated for longer time periods by not sending the command ending LF. So attacker could connect possibly from even a single IP and create 1000 connections to allocate 1 GB of memory, which would likely result in reaching VSZ limit and killing the process and its other proxied connections. Attacker could connect possibly from even a single IP and create 1000 connections to allocate 1 GB of memory, which would likely result in reaching VSZ limit and killing the process and its other proxied connections. Install fixed version, there is no other remediation. No publicly available exploits are known.

Vulnerability class: DoS (Denial of Service)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L.

EPSS exploit prediction

EPSS: 0.008 (56.3th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 56th percentile — 56.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-27857: held from 0.007 to 0.008.

EPSS over last 30 days · oldest: 0.007 · newest: 0.008 · change: +0.001

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-27857?
CVE-2026-27857 is a medium-severity vulnerability in Dovecot, classified under Uncontrolled Resource Consumption. CVSS score: 4.3/10. Published 2026-03-27.
How severe is CVE-2026-27857?
Medium severity. CVSS v3 base score is 4.3 out of 10.