CVE-2026-40013: Buffer Underwrite ('Buffer Underflow') in Open-Xchange GmbH OX Dovecot Pro
Description
CVE-2026-40013 is a buffer underwrite vulnerability in Open-Xchange GmbH OX Dovecot Pro's ManageSieve service. An attacker with valid credentials can submit a Sieve script containing an extreme numeric literal that triggers an out-of-bounds write during script compilation. This causes memory corruption and crashes the ManageSieve process, resulting in denial of service for script management. There are no known public exploits. Disabling the ManageSieve service if not needed and updating to a non-vulnerable version are recommended.
CVSS v3.1
Score 4.3medium
Affected software
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability (CVE-2026-40013) affects the ManageSieve service of OX Dovecot Pro. When a user with valid credentials submits a Sieve script containing an extreme numeric literal, the ManageSieve service's script compiler performs an out-of-bounds write (buffer underwrite), causing memory corruption and crashing the process. This leads to denial of service for remote Sieve script management. While remote code execution might be possible, this has not been confirmed. The vulnerability is identified as CWE-124 (Buffer Underwrite).
Potential Impact
The primary impact is denial of service due to the ManageSieve process crashing when processing malicious scripts. There is no confirmed confidentiality or integrity impact. Remote code execution is a theoretical possibility but not demonstrated. No public exploits are known.
Mitigation Recommendations
Update to a non-vulnerable version of OX Dovecot Pro when available. If remote Sieve script management is not required, disable the ManageSieve service to prevent exploitation. No public exploits exist, so immediate emergency action is not required beyond these steps.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- GHSA-jh33-8ccj-9h78
- Osv Schema Version
- 1.4.0
- Aliases
- ["CVE-2026-40013"]
- Database Specific Severity
- MODERATE
- Cvss Version
- 3.1
Threat ID: 6a91a7bdacd9273b49065178
Added to database: 08/28/2026, 15:22:37 UTC
Last enriched: 09/10/2026, 02:22:56 UTC
Last updated: 10/12/2026, 18:48:19 UTC
Views: 29
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