Log in Start free

Vulnerability · Published Aug 28, 2026 · Assigned by OX

CVE-2026-40203

Low 3.7

In plain English

A low-severity information exposure in OX Dovecot CE from Open-Xchange GmbH. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 17% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)3.7Low
Exploit odds (30 days)0.3%top 82.5% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

When IMAP compression is enabled, the same compression state is reused across responses in a session, so response sizes depend on both attacker-supplied mail and other mail in the same mailbox. An attacker that can send mail to a user and can also observe the sizes of that user's IMAP traffic can confirm whether the body of a small message matches a guessed text. Recovery of arbitrary unknown content was not demonstrated, but the attack can disclose whether a secret-like message body matches a candidate. Disable IMAP compression. Update to non-vulnerable version. No publicly available exploits are known.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Alpine:v3.23dovecot2.4.5-r0ALPINE-CVE-2026-40203
Alpine:v3.24dovecot2.4.5-r0ALPINE-CVE-2026-40203
Debian:12dovecot1:2.3.19.1+dfsg1-2.1+deb12u7DEBIAN-CVE-2026-40203
Debian:13dovecot1:2.4.1+dfsg1-6+deb13u7DEBIAN-CVE-2026-40203
Debian:14dovecot1:2.4.5+dfsg1-1DEBIAN-CVE-2026-40203
Ubuntu:22.04:LTSdovecotno fix listedUBUNTU-CVE-2026-40203
Ubuntu:24.04:LTSdovecotno fix listedUBUNTU-CVE-2026-40203
Ubuntu:26.04:LTSdovecotno fix listedUBUNTU-CVE-2026-40203

Affected products (as reported)

VendorProductVersions
Open-Xchange GmbH OX Dovecot Pro 2.3.0 – before 2.3.22.23.0.0 – before 3.0.73.1.0 – before 3.1.6
Open-Xchange GmbH OX Dovecot CE 2.3.0 – before 2.4.5

Weakness: CWE-200 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

References