Bug 2452177 (CVE-2026-27855)

Summary: CVE-2026-27855 dovecot: Dovecot: Replay attack allows unauthorized login via observed One-Time Password (OTP) exchange
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: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Dovecot. Under specific conditions, if the authentication cache is enabled and the username is altered in the password database, Dovecot's One-Time Password (OTP) authentication is vulnerable to a replay attack. A remote attacker able to observe an OTP exchange can exploit this flaw to log in as the legitimate user, leading to unauthorized access.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-03-27 09:02:16 UTC 
Dovecot OTP authentication is vulnerable to replay attack under specific conditions. If auth cache is enabled, and username is altered in passdb, then OTP credentials can be cached so that same OTP reply is valid. An attacker able to observe an OTP exchange is able to log in as the user. If authentication happens over unsecure connection, switch to SCRAM protocol. Alternatively ensure the communcations are secured, and if possible switch to OAUTH2 or SCRAM. No publicly available exploits are known.