CVE-2026-33263
MEDIUMDescription
When mail_max_userip_connections is set (default 10) and reached, submission-login can crash with epoll() panic caused by file descriptor handling issues. If running in high-security mode (default for community releases), only the new submission connection gets terminated. If running in high-performance mode (default for Pro releases), all connections handled by the submission-login process will be terminated. The crashes can cause failure for user to send a message, or it can cause duplicate messages to be sent. If TLS is not used (in the backend server processing the submission), duplicate deliveries cannot happen, because the crash can only happen at AUTH stage. Limit the number of connections handled by single submission-login process. This has a performance impact though. Update to non-vulnerable version. No publicly available exploits are known.
How to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Exploit Intelligence
Low risk: more likely to be exploited than 21% of all known CVEs.
References
Related Vulnerabilities
Other CWE-403 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2024-21626 | High | 8.6 | 18% | - | Fix |
| CVE-2024-58280 | High | 8.8 | 0.9% | - | - |
| CVE-2025-15114 | Critical | 9.8 | 0.6% | - | - |
| CVE-2026-16526 | High | 8.8 | 0.5% | - | Fix |
| CVE-2026-12296 | Critical | 9.6 | 0.4% | - | Fix |
| CVE-2025-3032 | High | 7.4 | 0.4% | - | Fix |
Common questions
How do I fix CVE-2026-33263?
No published fix for CVE-2026-33263 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
Is CVE-2026-33263 being actively exploited?
Not that we know of. CVE-2026-33263 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.29% is the estimated probability that it will be exploited in the next 30 days. That is higher than 21% of all scored CVEs.
How severe is CVE-2026-33263?
CVE-2026-33263 has a CVSS v3 base score of 4.3, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-08-28.