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Fencer Vulns
high 7.5

CVE-2026-42391 json

An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, which causes memory and C…

published 2026-08-28 2 mo ago modified 2026-09-03 2 mo ago also EUVD-2026-67674

cvss
7.5
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 39%
public exploits
0
none known

Summary

An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, which causes memory and CPU usage to grow disproportionately. The login process can be terminated by the out-of-memory handling, which also terminates all other connections handled by the same process. This can cause degradation or denial of service for IMAP logins. Limit the number of connections handled by a single imap-login process. This has a performance impact though. Update to non-vulnerable version. No publicly available exploits are known.

Patch / fix

  • Open-Xchange GmbH OX Dovecot Pro 2.3.22.2, 3.0.7, 3.1.6
  • Open-Xchange GmbH OX Dovecot CE 2.4.5
  • dovecot Debian 12 1:2.3.19.1+dfsg1-2.1+deb12u7
  • dovecot Debian 13 1:2.4.1+dfsg1-6+deb13u7
  • dovecot Debian 14 1:2.4.5+dfsg1-1

debian advisories DEBIAN-CVE-2026-42391

  • dovecot RHEL 9 1:2.3.16-18.el9_8.8
  • dovecot-mysql RHEL 9 1:2.3.16-18.el9_8.8
  • dovecot-pgsql RHEL 9 1:2.3.16-18.el9_8.8
  • dovecot-pigeonhole RHEL 9 1:2.3.16-18.el9_8.8
  • dovecot RHEL 10.2 1:2.3.21-19.el10_2.8
  • dovecot-mysql RHEL 10.2 1:2.3.21-19.el10_2.8
  • dovecot-pgsql RHEL 10.2 1:2.3.21-19.el10_2.8
  • dovecot-pigeonhole RHEL 10.2 1:2.3.21-19.el10_2.8

red hat advisories RHSA-2026:80825RHSA-2026:79371RHSA-2026:76763

  • 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 2.4.4-160000.2.1
  • dovecot22 SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS 2.2.31-19.40.1

suse advisories SUSE-SU-2026:4139-1SUSE-SU-2026:3919-1SUSE-SU-2026:23595-1

  • dovecot24 openSUSE Leap 16.0 2.4.4-160000.2.1
  • dovecot24 openSUSE Tumbleweed 2.4.5-1.1

opensuse advisories openSUSE-SU-2026:21720-1openSUSE-SU-2026:11629-1

  • dovecot AlmaLinux 9 1:2.3.16-18.el9_8.8
  • dovecot-mysql AlmaLinux 9 1:2.3.16-18.el9_8.8
  • dovecot-pgsql AlmaLinux 9 1:2.3.16-18.el9_8.8
  • dovecot-pigeonhole AlmaLinux 9 1:2.3.16-18.el9_8.8
  • dovecot AlmaLinux 10 1:2.3.21-19.el10_2.8
  • dovecot-mysql AlmaLinux 10 1:2.3.21-19.el10_2.8
  • dovecot-pgsql AlmaLinux 10 1:2.3.21-19.el10_2.8
  • dovecot-pigeonhole AlmaLinux 10 1:2.3.21-19.el10_2.8

almalinux advisories ALSA-2026:80825ALSA-2026:79371ALSA-2026:76763

  • dovecot Rocky Linux 9 1:2.3.16-18.el9_8.8
  • dovecot Rocky Linux 10 1:2.3.21-19.el10_2.8
  • dovecot Rocky Linux 8 1:2.3.16-16.el8_10

rocky linux advisories RLSA-2026:80825RLSA-2026:79371RLSA-2026:76763

  • dovecot Alpine 3.24, Alpine 3.23 2.4.5-r0

alpine advisories ALPINE-CVE-2026-42391

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-2026-42391 updated cvss 7.5

dovecot: Dovecot: Denial of Service via IMAP ID command with excessive parameters

  • Red Hat Enterprise Linux 6 dovecot, dovecot-mysql, dovecot-pgsql, dovecot-pigeonhole
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 dovecot, dovecot-mysql, dovecot-pgsql, dovecot-pigeonhole
    affected: workaround, no fix available
  • Red Hat Enterprise Linux AppStream (v. 8) dovecot 2.3.16-16.el8_10, dovecot-mysql 2.3.16-16.el8_10, dovecot-pgsql 2.3.16-16.el8_10, dovecot-pigeonhole 2.3.16-16.el8_10
    fixed: vendor fix RHSA-2026:76763
  • Red Hat Enterprise Linux AppStream (v. 9) dovecot 2.3.16-18.el9_8.8, dovecot-mysql 2.3.16-18.el9_8.8, dovecot-pgsql 2.3.16-18.el9_8.8, dovecot-pigeonhole 2.3.16-18.el9_8.8
    fixed: vendor fix RHSA-2026:80825
  • Red Hat Enterprise Linux AppStream (v. 10) dovecot 2.3.21-19.el10_2.8, dovecot-mysql 2.3.21-19.el10_2.8, dovecot-pgsql 2.3.21-19.el10_2.8, dovecot-pigeonhole 2.3.21-19.el10_2.8
    fixed: vendor fix RHSA-2026:79371
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) dovecot 2.3.16-18.el9_8.8
    fixed: vendor fix RHSA-2026:80825
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) dovecot-devel 2.3.21-19.el10_2.8, dovecot-debuginfo 2.3.21-19.el10_2.8, dovecot-debugsource 2.3.21-19.el10_2.8, dovecot-mysql-debuginfo 2.3.21-19.el10_2.8, dovecot-pgsql-debuginfo 2.3.21-19.el10_2.8, dovecot-pigeonhole-debuginfo 2.3.21-19.el10_2.8
    fixed: vendor fix RHSA-2026:79371
  • Red Hat Enterprise Linux CRB (v. 8) dovecot 2.3.16-16.el8_10
    fixed: vendor fix RHSA-2026:76763

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
2 mo ago

Exploit prediction

0.45% chance of exploitation in the next 30 days, higher than 39% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Open-Xchange GmbH OX Dovecot Pro
  • Open-Xchange GmbH OX Dovecot CE

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.