Resource exhaustion in Dovecot and OX Dovecot Pro - CVE-2026-27857

Vulnerability identifier: #VU124728

CSH Severity: Medium

CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:L/E:U/U:Green

CVE-ID: CVE-2026-27857

CWE-ID: CWE-400

Exploitation vector: Remote access

Exploit availability: No public exploit available

Affected software:
Dovecot
OX Dovecot Pro
SUSE Linux Enterprise Server 12 SP5 LTSS Extended
SUSE Linux Enterprise Server 12 SP5
SUSE Linux Enterprise Server for SAP Applications 12
SUSE Linux Enterprise Server 12
SUSE Linux Enterprise High Performance Computing 12
Red Hat Enterprise Linux for x86_64
Red Hat Enterprise Linux for IBM z Systems
Red Hat Enterprise Linux for Power, little endian
Red Hat Enterprise Linux for ARM 64
Red Hat CodeReady Linux Builder for x86_64
Red Hat CodeReady Linux Builder for Power, little endian
Red Hat CodeReady Linux Builder for ARM 64
Red Hat CodeReady Linux Builder for IBM z Systems
Anolis OS
Red Hat Enterprise Linux Server - AUS
Red Hat Enterprise Linux Server - TUS
Red Hat Enterprise Linux for ARM 64 - Extended Update Support
Red Hat Enterprise Linux for Power, little endian - Extended Update Support
Red Hat Enterprise Linux for IBM z Systems - Extended Update Support
Red Hat Enterprise Linux for x86_64 - Extended Update Support
Red Hat CodeReady Linux Builder for ARM 64 - Extended Update Support
Red Hat CodeReady Linux Builder for Power, little endian - Extended Update Support
Red Hat CodeReady Linux Builder for x86_64 - Extended Update Support
Red Hat CodeReady Linux Builder for IBM z Systems - Extended Update Support
openEuler
Ubuntu
Fedora
Red Hat Enterprise Linux Server for Power LE - Update Services for SAP Solutions
dovecot22-backend-mysql
dovecot22-backend-sqlite
dovecot22-devel
dovecot22
dovecot22-debuginfo
dovecot22-backend-pgsql
dovecot22-backend-mysql-debuginfo
dovecot22-backend-sqlite-debuginfo
dovecot22-debugsource
dovecot22-backend-pgsql-debuginfo
dovecot (Red Hat package)
dovecot-help
dovecot-devel
dovecot-debugsource
dovecot-debuginfo
dovecot
dovecot (Ubuntu package)
dovecot-pigeonhole
dovecot-mysql
dovecot-pgsql

The vulnerability allows a remote user to cause a denial of service.

The vulnerability exists due to uncontrolled resource consumption in imap-login process when handling malformed NOOP commands. A remote user can send a specially crafted command with excessive parentheses to cause a denial of service.

Install security update from vendor's website.

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