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    CVE-2026-27855

    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.

    Published:Mar 27, 2026
    Last Modified:Apr 29, 2026
    EPS:Mar 27, 2026
    EPSS Score:0.00047
    CVSS Score:6.8

    Affected Products

    Vendor
    Dovecot
    Product
    Dovecot
    Vendor
    Open-xchange
    Product
    Dovecot
    Vendor
    Open-xchange
    Product
    Ox Dovecot Pro

    Exploits

    No exploit reference

    Related CVEs

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    CVE-2026-27851 (CVSS 7.4) — When safe filter is used with variable expansion, all following pipelines on the same string are incorrectly i…
    CVE-2026-27860 (CVSS 3.7) — If auth_username_chars is empty, it is possible to inject arbitrary LDAP filter to Dovecot's LDAP authenticati…
    CVE-2026-27859 (CVSS 5.3) — A mail message containing excessive amount of RFC 2231 MIME parameters causes LMTP to use too much CPU. A suit…
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    CVE-2026-27857 (CVSS 4.3) — Sending "NOOP (((...)))" command with 4000 parenthesis open+close results in ~1MB extra memory usage. Longer c…
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    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High