Bug 2476470 (CVE-2026-40016)

Summary: CVE-2026-40016 dovecot: Dovecot: Denial of Service due to Sieve script CPU limit bypass
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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 or local attacker could upload a malicious Sieve script through the ManageSieve service, or locally, to bypass configured CPU time limits for Sieve scripts. This allows the attacker to consume excessive server resources, leading to a degradation of server performance and a Denial of Service (DoS).
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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: 2481121, 2481122, 2481123    
Bug Blocks:    

Description OSIDB Bzimport 2026-05-12 14:01:52 UTC 
Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured CPU time limits for Sieve up to 130 times of the configured limit. Attacker can use this to degrade server performance and bypass configured CPU time limits for Sieve scripts. Install fixed version, or alternatively prevent direct access to Sieve scripts via ManageSieve or local access. No publicly available exploits are known.