High [CVE-2026-42391] Denial of Service via IMAP ID command with excessive parameters
This high-severity Red Hat Linux advisory covers CVE-2026-42391 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7.
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Summary
An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, which causes memory and CPU usage to grow disproportionately. The login process can be terminated by the out-of-memory handling, which also terminates all other connections handled by the same process.
This can cause degradation or denial of service for IMAP logins. Limit the number of connections handled by a single imap-login process.
This has a performance impact though. Update to non-vulnerable version.
No publicly available exploits are known. A flaw was found in Dovecot.
This action causes the server to consume excessive memory and CPU resources, leading to the termination of login processes and other active connections. Red Hat severity: Important — CVSS 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
Weakness: CWE-770. Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9.
Will not fix / out of support: Red Hat Enterprise Linux 6. Red Hat does not currently list a fixing RHSA for this CVE.
Affected products named by the advisory: Red Hat package: dovecot.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
Mitigation checklist
- To mitigate this issue, limit the number of connections handled by a single `imap-login` process by adjusting the `process_limit` setting within the `service imap-login` block in your Dovecot configuration (e.g., `/etc/dovecot/dovecot.conf`). Increasing `process_limit` will cause Dovecot to spawn more `imap-login` processes, distributing connections more widely and reducing the impact of a single malicious connection. For example, to set the process limit to 200: ``` # /etc/dovecot/dovecot.conf service imap-login { process_limit = 200 } ``` After modifying the configuration, restart the Dovecot service for the changes to take effect. This may impact performance due to increased process overhead. ```bash systemctl restart dovecot ```
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
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