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Fencer Vulns
medium 5.3

CVE-2026-27859 json

A mail message containing excessive amount of RFC 2231 MIME parameters causes LMTP to use too much CPU.

published 2026-03-27 7 mo ago modified 2026-10-26 14 d ago also EUVD-2026-16571

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 32%
public exploits
0
none known

Summary

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.

Patch / fix

  • dovecot dovecot 2.4.3, 3.0.5, 3.1.5
  • open-xchange dovecot 2.4.3, 3.0.5, 3.1.5
  • dovecot Debian 12 1:2.3.19.1+dfsg1-2.1+deb12u2
  • dovecot Debian 13 1:2.4.1+dfsg1-6+deb13u4
  • dovecot Debian 14 1:2.4.3+dfsg1-1

debian advisories DEBIAN-CVE-2026-27859

  • dovecot Ubuntu 22.04 LTS 1:2.3.16+dfsg1-3ubuntu2.7
  • dovecot Ubuntu 24.04 LTS 1:2.3.21+dfsg1-2ubuntu6.3
  • dovecot Ubuntu 25.10 1:2.4.1+dfsg1-5ubuntu4.1

ubuntu advisories UBUNTU-CVE-2026-27859

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • dovecot23 SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +8 more 2.3.21.1-150200.76.1
  • dovecot24 SLES for SAP applications 16.0, SLES 16.0 2.4.3-160000.1.1

suse advisories SUSE-SU-2026:4139-1SUSE-SU-2026:21208-1

  • dovecot24 openSUSE Leap 16.0 2.4.3-160000.1.1
  • dovecot24 openSUSE Tumbleweed 2.4.3-1.1

opensuse advisories openSUSE-SU-2026:20554-1openSUSE-SU-2026:10442-1

  • dovecot Alpine 3.24, Alpine 3.23 2.4.3-r0

alpine advisories ALPINE-CVE-2026-27859

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-27859 updated cvss 5.3

dovecot: Dovecot: Denial of Service via excessive RFC 2231 MIME parameters

  • Red Hat Enterprise Linux 6 dovecot, dovecot-mysql, dovecot-pgsql, dovecot-pigeonhole
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 dovecot, dovecot-mysql, dovecot-pgsql, dovecot-pigeonhole Red Hat Enterprise Linux 8 dovecot, dovecot-mysql, dovecot-pgsql, dovecot-pigeonhole Red Hat Enterprise Linux 9 dovecot, dovecot-mysql, dovecot-pgsql, dovecot-pigeonhole Red Hat Enterprise Linux 10 dovecot
    affected: no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
7 mo ago

Exploit prediction

0.38% chance of exploitation in the next 30 days, higher than 32% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Affected products

  • Open-Xchange GmbH OX Dovecot Pro

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.