dovecot: Dovecot: Denial of Service and potential message duplication via connection limit exhaustion
Published Aug 28, 2026
7.1
HIGHCVSS 3.1
EPSS 0.55%
Description
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.
Affected products
-
- Version 2.3.0StatusaffectedConstraints<2.4.5
- Version
-
- Version 2.3.0StatusaffectedConstraints<2.3.22.2
- Version 3.0.0StatusaffectedConstraints<3.0.7
- Version 3.1.0StatusaffectedConstraints<3.1.6
- Version
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Open-Xchange GmbH | OX Dovecot CE | unaffected |
| ||||||||||||
| Open-Xchange GmbH | OX Dovecot Pro | unaffected |
|
No data.
No data.
Red Hat Enterprise Linux 10
dovecot
Affected
Red Hat Enterprise Linux 6
dovecot
Out of support scope
Red Hat Enterprise Linux 7
dovecot
Affected
Red Hat Enterprise Linux 8
dovecot
Affected
Red Hat Enterprise Linux 9
dovecot
Affected
| Product | Package | State | Advisory |
|---|---|---|---|
| Red Hat Enterprise Linux 10 | dovecot | Affected | n/a |
| Red Hat Enterprise Linux 6 | dovecot | Out of support scope | n/a |
| Red Hat Enterprise Linux 7 | dovecot | Affected | n/a |
| Red Hat Enterprise Linux 8 | dovecot | Affected | n/a |
| Red Hat Enterprise Linux 9 | dovecot | Affected | n/a |
No package ranges for this CVE.
Remediation
Red Hat mitigation
To mitigate this issue, limit the number of connections handled by a single submission-login process. This can be achieved by adjusting the `process_limit` setting for the `submission-login` service in the Dovecot configuration. For example, add or modify the following in a Dovecot configuration file (e.g., `/etc/dovecot/conf.d/10-master.conf`): ``` service submission-login { process_limit = <lower_value> } ``` Reducing this limit may impact performance. After modifying the configuration, restart the Dovecot service for the changes to take effect.
References (6)
- https://access.redhat.com/security/cve/CVE-2026-33263 Vendor Advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=2525567 Issue Tracking
- https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0003.json vendor-advisory
- https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-67658 Advisory
- https://nvd.nist.gov/vuln/detail/CVE-2026-33263
- https://www.cve.org/CVERecord?id=CVE-2026-33263
Change history (0)
No recorded changes yet.