CVE-2026-27857

NameCVE-2026-27857
DescriptionSending "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.
SourceCVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)

Vulnerable and fixed packages

The table below lists information on source packages.

Source PackageReleaseVersionStatus
dovecot (PTS)bullseye1:2.3.13+dfsg1-2+deb11u1vulnerable
bullseye (security)1:2.3.13+dfsg1-2+deb11u2vulnerable
bookworm, bookworm (security)1:2.3.19.1+dfsg1-2.1+deb12u1vulnerable
trixie1:2.4.1+dfsg1-6+deb13u3vulnerable
trixie (security)1:2.4.1+dfsg1-6+deb13u1vulnerable
forky, sid1:2.4.2+dfsg1-4vulnerable

The information below is based on the following data on fixed versions.

PackageTypeReleaseFixed VersionUrgencyOriginDebian Bugs
dovecotsource(unstable)(unfixed)

Notes

https://documentation.open-xchange.com/dovecot/security/advisories/html/2026/oxdc-adv-2026-0001.html#cve-2026-27857-imap-login-excessive-memory-usage-dos

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