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Fencer Vulns
high 7.4

CVE-2026-27856 json

Doveadm credentials are verified using direct comparison which is susceptible to timing oracle attack.

published 2026-03-27 7 mo ago modified 2026-10-26 13 d ago also EUVD-2026-16565

cvss
7.4
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 34%
public exploits
0
none known

Summary

Doveadm credentials are verified using direct comparison which is susceptible to timing oracle attack. An attacker can use this to determine the configured credentials. Figuring out the credential will lead into full access to the affected component. Limit access to the doveadm http service port, install fixed version. No publicly available exploits are known.

Patch / fix

  • Red Hat Red Hat Enterprise Linux 7 Extended Lifecycle Support 1:2.2.36-8.el7_9.1
  • 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-2026-27856

  • 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-2026-27856

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

  • dovecot RHEL 7 ELS 1:2.2.36-8.el7_9.1
  • dovecot-mysql RHEL 7 ELS 1:2.2.36-8.el7_9.1
  • dovecot-pgsql RHEL 7 ELS 1:2.2.36-8.el7_9.1
  • dovecot-pigeonhole RHEL 7 ELS 1:2.2.36-8.el7_9.1

red hat advisories RHSA-2026:26564

  • 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-2026-27856

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-2026-27856 updated cvss 7.4

dovecot: Doveadm: Full access via timing oracle attack in credential verification

  • Red Hat Enterprise Linux 6 dovecot, dovecot-mysql, dovecot-pgsql, dovecot-pigeonhole
    affected: no fix available
  • Red Hat Enterprise Linux Server (v. 7 ELS) dovecot 2.2.36-8.el7_9.1, dovecot-mysql 2.2.36-8.el7_9.1, dovecot-pgsql 2.2.36-8.el7_9.1, dovecot-pigeonhole 2.2.36-8.el7_9.1 Red Hat Enterprise Linux Server Optional (v. 7 ELS) dovecot-devel 2.2.36-8.el7_9.1, dovecot-debuginfo 2.2.36-8.el7_9.1
    fixed: vendor fix RHSA-2026:26564
  • 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
    not affected: vulnerable code not present

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
total
Assessed
7 mo ago

Exploit prediction

0.40% chance of exploitation in the next 30 days, higher than 34% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
CISA ADP 3.1 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
NVD 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected products

  • Open-Xchange GmbH OX Dovecot Pro
  • Red Hat Red Hat Enterprise Linux 7 Extended Lifecycle Support
  • Red Hat Red Hat Enterprise Linux 10
  • Red Hat Red Hat Enterprise Linux 6
  • Red Hat Red Hat Enterprise Linux 8
  • Red Hat Red Hat Enterprise Linux 9

Classification

Weakness
  • CWE-287 Improper Authentication
  • CWE-208 Observable Timing Discrepancy

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.