Medium [CVE-2026-40014] Denial of Service via crafted IMAP THREAD command
This medium-severity Red Hat Linux advisory covers CVE-2026-40014 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7.
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Summary
An attacker that can send mail to a user can craft a message header that makes the IMAP THREAD command consume CPU disproportionate to the size of the message. When a mail client issues a THREAD command on the affected mailbox, this can cause degradation or denial of service for IMAP.
Monitor system for abnormal CPU usage, kill the offending process and remove the offending message from the affected mailbox. Update to non-vulnerable version.
No publicly available exploits are known. A flaw was found in Dovecot.
Red Hat severity: Moderate — CVSS 6.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H). Weakness: CWE-606.
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 52 minutes 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 52 minutes ago·verify at source
Mitigation checklist
- To mitigate this issue, administrators should monitor Dovecot processes for abnormal CPU usage. If high CPU consumption is observed, identify and terminate the offending Dovecot process. Subsequently, remove the malicious email from the affected mailbox to prevent re-triggering the vulnerability. Restarting the Dovecot service may be required after process termination, which could temporarily impact mail service availability.
Official advisory · high-confidence parse· fetched 52 minutes ago·verify at source
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