CVE-2026-33263 Open-Xchange GmbH CVE debrief

Who should care

Administrators and users of the affected product, particularly those using the submission-login process, should be aware of this vulnerability and take steps to mitigate its effects. This includes reviewing the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance, and planning vendor-supported updates or mitigations through normal change control where exposure is confirmed.

Technical summary

The vulnerability occurs when the mail_max_userip_connections setting is reached, causing submission-login to crash with an epoll() panic due to file descriptor handling issues. This can lead to failures in sending messages or duplicate messages being sent. The crashes can be mitigated by limiting the number of connections handled by a single submission-login process, although this may have a performance impact. No publicly available exploits are known. The vulnerability has a CVSS score of 4.3 and a severity of MEDIUM.

Defensive priority

This vulnerability has a CVSS score of 4.3 and a severity of MEDIUM. To address this issue, consider updating to a non-vulnerable version of the affected product.

Recommended defensive actions

• Update to a non-vulnerable version of the affected product.
• Limit the number of connections handled by a single submission-login process to mitigate potential crashes.
• 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.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.
• 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.

Evidence notes

The vulnerability occurs when the mail_max_userip_connections setting is reached, causing submission-login to crash with an epoll() panic due to file descriptor handling issues. This can lead to failures in sending messages or duplicate messages being sent. The crashes can be mitigated by limiting the number of connections handled by a single submission-login process, although this may have a performance impact.

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.