Bug 2525560 (CVE-2026-40017)

Summary: CVE-2026-40017 dovecot: Dovecot: Denial of Service via crafted IMAP message headers
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Dovecot. A remote attacker who can send mail to a user can craft a message header designed to cause collisions in an internal hash table. This manipulation forces the IMAP THREAD command to consume excessive CPU resources, leading to degradation or a complete denial of service for the IMAP server. This can disrupt email services for affected users.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Bug Depends On: 2526675    
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Description OSIDB Bzimport 2026-08-28 11:22:51 UTC 
An attacker that can send mail to a user can craft a message header whose values are chosen to collide in an internal hash table, which makes the IMAP THREAD command consume CPU disproportionate to the size of the message. This is a separate issue from CVE-2026-40014 and is not addressed by that fix. Whenever 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.