Improper Authentication in Dovecot and OX Dovecot Pro - CVE-2026-27856

Vulnerability identifier: #VU124730

CSH Severity: High

CVSS v4: 9.1 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-27856

CWE-ID: CWE-287

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to bypass authentication.

The vulnerability exists due to improper authentication in doveadm credentials verification when comparing provided credentials. A remote attacker can perform timing oracle attack to bypass authentication.

Dovecot
OX Dovecot Pro
SUSE Linux Enterprise Server 12 SP5
SUSE Linux Enterprise Server 12 SP5 LTSS Extended
SUSE Linux Enterprise High Performance Computing 12
SUSE Linux Enterprise Server 12
SUSE Linux Enterprise Server for SAP Applications 12
openEuler
Ubuntu
dovecot22-backend-mysql
dovecot22-backend-sqlite
dovecot22-devel
dovecot22
dovecot22-debuginfo
dovecot22-backend-pgsql
dovecot22-backend-mysql-debuginfo
dovecot22-backend-pgsql-debuginfo
dovecot22-debugsource
dovecot22-backend-sqlite-debuginfo
dovecot (Red Hat package)
dovecot-help
dovecot-devel
dovecot-debugsource
dovecot-debuginfo
dovecot
dovecot (Ubuntu package)

Install security update from vendor's website.

Dovecot - update to 2.4.3
OX Dovecot Pro - addressed in versions 2.3.22.1, 3.0.5, 3.1.4
dovecot22-backend-mysql - update to 2.2.31-19.32.1
dovecot22-backend-sqlite - update to 2.2.31-19.32.1
dovecot22-devel - update to 2.2.31-19.32.1
dovecot22 - update to 2.2.31-19.32.1
dovecot22-debuginfo - update to 2.2.31-19.32.1
dovecot22-backend-pgsql - update to 2.2.31-19.32.1
dovecot22-backend-mysql-debuginfo - update to 2.2.31-19.32.1
dovecot22-backend-pgsql-debuginfo - update to 2.2.31-19.32.1
dovecot22-debugsource - update to 2.2.31-19.32.1
dovecot22-backend-sqlite-debuginfo - update to 2.2.31-19.32.1
dovecot (Red Hat package) - update to 2.2.36-8.el7_9.1
dovecot-help - update to 2.3.15-7
dovecot-devel - update to 2.3.15-7
dovecot-debugsource - update to 2.3.15-7
dovecot-debuginfo - update to 2.3.15-7
dovecot - update to 2.3.15-7
dovecot (Ubuntu package) - addressed in versions 1:2.3.16+dfsg1-3ubuntu2.7, 1:2.3.16+dfsg1-3ubuntu2.8, 1:2.3.21+dfsg1-2ubuntu6.3, 1:2.3.21+dfsg1-2ubuntu6.4, 1:2.4.1+dfsg1-5ubuntu4.1

• https://documentation.open-xchange.com/dovecot/security/advisories/html/2026/oxdc-adv-2026-0001.html

• Multiple vulnerabilities in Dovecot
• Ubuntu update for dovecot
• openEuler update for dovecot
• SUSE update for dovecot22
• Ubuntu update for dovecot
• Red Hat Enterprise Linux 7 Extended Lifecycle Support update for dovecot