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 leads to memory corruption and crashes the ManageSieve process, causing 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
Open-Xchange GmbH
OX Dovecot Pro
Open-Xchange GmbH
OX Dovecot CE
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability involves a buffer underwrite (buffer underflow) triggered by submitting a Sieve script with an extreme numeric literal to the ManageSieve service in OX Dovecot Pro. The out-of-bounds write occurs during compilation of the script, causing memory corruption and crashing the ManageSieve process, resulting in denial of service. The vulnerability requires valid credentials to exploit. There is a potential for remote code execution, but this is not confirmed. No public exploits are known at this time.
Potential Impact
The primary impact is denial of service due to the ManageSieve process crashing when processing malicious Sieve scripts. While remote code execution might be possible, this has not been confirmed or observed. The vulnerability requires attacker authentication (valid credentials) to exploit.
Mitigation Recommendations
No official patch or remediation level is currently confirmed. It is recommended to disable the ManageSieve service if remote Sieve script management is not needed. Users should update to a non-vulnerable version once available. Monitor vendor advisories for patch releases.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- OX
- Date Reserved
- 2026-04-08T09:59:59.342Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6a916f87acd9273b49cf91c3
Added to database: 08/28/2026, 11:22:47 UTC
Last enriched: 09/10/2026, 02:53:21 UTC
Last updated: 10/12/2026, 18:48:19 UTC
Views: 37
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