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Fencer Vulns
medium 5.3

CVE-2026-40016 json

Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured CPU time limits for Sieve up to 130…

published 2026-05-12 5 mo ago modified 2026-10-26 13 d ago also EUVD-2026-29470

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 27%
public exploits
0
none known

Summary

Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured CPU time limits for Sieve up to 130 times of the configured limit. Attacker can use this to degrade server performance and bypass configured CPU time limits for Sieve scripts. Install fixed version, or alternatively prevent direct access to Sieve scripts via ManageSieve or local access. No publicly available exploits are known.

Patch / fix

  • dovecot dovecot 2.4.4, 3.1.5
  • open-xchange dovecot 2.4.4, 3.1.5
  • dovecot Debian 12 1:2.3.19.1+dfsg1-2.1+deb12u6
  • dovecot Debian 13 1:2.4.1+dfsg1-6+deb13u6
  • dovecot Debian 14 1:2.4.4+dfsg1-1

debian advisories DEBIAN-CVE-2026-40016

  • dovecot Ubuntu 22.04 LTS 1:2.3.16+dfsg1-3ubuntu2.9
  • dovecot Ubuntu 24.04 LTS 1:2.3.21+dfsg1-2ubuntu6.5
  • dovecot Ubuntu 25.10 1:2.4.1+dfsg1-5ubuntu4.2
  • dovecot Ubuntu 26.04 LTS 1:2.4.2+dfsg1-3ubuntu2.1

ubuntu advisories UBUNTU-CVE-2026-40016

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 2.4.4-160000.1.1
  • dovecot22 SLES LTSS Extended Security 12 SP5 2.2.31-19.43.1

suse advisories SUSE-SU-2026:4271-1SUSE-SU-2026:4139-1SUSE-SU-2026:22185-1

  • dovecot24 openSUSE Leap 16.0 2.4.4-160000.1.1
  • dovecot24 openSUSE Tumbleweed 2.4.4-1.1

opensuse advisories openSUSE-SU-2026:21109-1openSUSE-SU-2026:10766-1

  • dovecot Alpine 3.24, Alpine 3.23 2.4.4-r0

alpine advisories ALPINE-CVE-2026-40016

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-2026-40016 updated cvss 6.5

dovecot: Dovecot: Denial of Service due to Sieve script CPU limit bypass

  • Red Hat Enterprise Linux 6 dovecot, dovecot-mysql, dovecot-pgsql, dovecot-pigeonhole Red Hat Enterprise Linux 8 dovecot, dovecot-mysql, dovecot-pgsql, dovecot-pigeonhole
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Enterprise Linux 9 dovecot, dovecot-mysql, dovecot-pgsql, dovecot-pigeonhole
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 10 dovecot
    affected: workaround, 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
no
Technical impact
partial
Assessed
5 mo ago

Exploit prediction

0.34% chance of exploitation in the next 30 days, higher than 27% 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:H/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

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.