IMAP Compression Vulnerability in Dovecot Mail Server by Open-Xchange
CVE-2026-40203

3.7LOW

Key Information:

Vendor

Open-xchange Gmbh

Status
Ox Dovecot Pro
Ox Dovecot Ce
Vendor
CVE Published:
28 August 2026

What is CVE-2026-40203?

The vulnerability in Dovecot Mail Server arises when IMAP compression is enabled, causing the same compression state to be reused across responses during a session. This can lead to potential information leakage, as attackers who can observe the sizes of IMAP traffic may verify whether the body of a small message corresponds to a guessed text. Although recovery of arbitrary unknown content is not demonstrated, the risk of confirming the match between a candidate message and the body of a secret-like message poses a significant concern for data privacy. To mitigate this risk, it is advised to disable IMAP compression and ensure the server is updated to a secure version.

Affected Version(s)

OX Dovecot CE 2.3.0 < 2.4.5

OX Dovecot Pro 2.3.0 < 2.3.22.2

OX Dovecot Pro 3.0.0 < 3.0.7

References

https://documentation.open-xchange.com/dovecot/security/a...
vendor-advisory

CVSS V3.1

Score:
3.7
Severity:
LOW
Confidentiality:
Low
Integrity:
None
Availability:
Low
Attack Vector:
Network
Attack Complexity:
High
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.