CVE-2026-40013 Open-Xchange GmbH CVE debrief

Who should care

Administrators and users of the affected product who rely on the ManageSieve service for remote Sieve script management should be aware of this vulnerability and take necessary actions to mitigate the risk. This includes reviewing the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance. Operators, platform administrators, vulnerability management teams, and security teams should review the vulnerability details and plan vendor-supported updates or mitigations through normal change control where exposure is confirmed. Compensating controls for exposed systems should be reviewed while remediation is scheduled and verified. Relevant monitoring, detection, and logs for exposed assets should be checked for extra review. Exceptions, retested remediated assets, and closed items should be tracked only after evidence is documented. Asset inventory and security teams should confirm whether affected product deployments exist in managed environments and assign an owner for follow-up. Security teams should also track the vulnerability management process and verify that all necessary steps are taken to mitigate the risk. Vulnerability management teams should review compensating controls for exposed systems while remediation is scheduled and verified. Monitoring and detection teams should check relevant logs for exposed assets that need extra review. IT asset management teams should confirm whether affected product deployments exist in managed environments and assign an owner for follow-up. Security operations teams should review the vulnerability details and plan vendor-supported updates or mitigations through normal change control where exposure is confirmed. Security operations teams should also review compensating controls for exposed systems while remediation is scheduled and verified. Security operations teams should check relevant monitoring, detection, and logs for exposed assets that need extra review. Security operations teams should track exceptions, retest remediated assets, and close the item only after evidence is documented. Security operations teams should also review the vulnerability management process and verify

Technical summary

CVE-2026-40013 is a vulnerability in the ManageSieve service that allows an attacker with valid credentials to submit a malicious Sieve script, causing an out-of-bounds write and memory corruption, leading to a denial of service. The vulnerability has a CVSS score of 4.3 and a severity of MEDIUM. There are no known publicly available exploits. The vulnerability affects the ManageSieve service, which is used for remote Sieve script management. Administrators should prioritize updating to a non-vulnerable version of the affected product to prevent potential denial of service and remote code execution risks.

Defensive priority

Administrators should prioritize updating to a non-vulnerable version of the affected product to prevent potential denial of service and remote code execution risks.

Recommended defensive actions

• Disable the ManageSieve service if users do not need remote Sieve script management.
• Update to a non-vulnerable version of the affected product.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance.
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.

Evidence notes

The CVE-2026-40013 record indicates that an attacker with valid credentials can submit a malicious Sieve script, causing an out-of-bounds write and memory corruption in the ManageSieve service, leading to a denial of service. The potential for remote code execution is noted but not confirmed. Evidence is based on a CVE Program record and an NVD vulnerability detail page.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.