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    CVE-2026-27858

    Attacker can send a specifically crafted message before authentication that causes managesieve to allocate large amount of memory. Attacker can force managesieve-login to be unavailable by repeatedly crashing the process. Protect access to managesieve protocol, or install fixed version. No publicly available exploits are known.

    Published:Mar 27, 2026
    Last Modified:Apr 30, 2026
    EPS:Mar 27, 2026
    EPSS Score:0.00021
    CVSS Score:7.5

    Affected Products

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

    Exploits

    No exploit reference

    Related CVEs

    CVE-2026-42006 (CVSS 4.3) — An attacker can cause uncontrolled memory usage with excessive bracing over IMAP. The fix in CVE-2026-27857 wa…
    CVE-2026-40020 (CVSS 3.1) — Attacker can use the IMAP SETACL command to inject the anyone permission to user's dovecot-acl file even if im…
    CVE-2026-40016 (CVSS 5.3) — Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured CPU ti…
    CVE-2026-33603 (CVSS 6.8) — Attacker can use a specially crafted base64 exchange between Dovecot and Client to fake SCRAM TLS channel bind…
    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…
    CVE-2026-27857 (CVSS 4.3) — Sending "NOOP (((...)))" command with 4000 parenthesis open+close results in ~1MB extra memory usage. Longer c…
    CVE-2026-27856 (CVSS 7.4) — Doveadm credentials are verified using direct comparison which is susceptible to timing oracle attack. An atta…
    CVE-2026-27855 (CVSS 6.8) — Dovecot OTP authentication is vulnerable to replay attack under specific conditions. If auth cache is enabled,…

    References

    https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0001.json
    https://access.redhat.com/errata/RHSA-2026:13498
    https://access.redhat.com/errata/RHSA-2026:13830
    https://access.redhat.com/errata/RHSA-2026:13857
    https://access.redhat.com/errata/RHSA-2026:17602
    https://access.redhat.com/errata/RHSA-2026:17625
    https://access.redhat.com/errata/RHSA-2026:17626
    https://access.redhat.com/errata/RHSA-2026:17628
    https://access.redhat.com/errata/RHSA-2026:17630
    https://access.redhat.com/errata/RHSA-2026:18053
    https://access.redhat.com/errata/RHSA-2026:19149
    https://access.redhat.com/errata/RHSA-2026:19364
    https://access.redhat.com/errata/RHSA-2026:19453
    https://access.redhat.com/errata/RHSA-2026:19455
    https://access.redhat.com/errata/RHSA-2026:26564
    https://access.redhat.com/security/cve/CVE-2026-27858
    https://bugzilla.redhat.com/show_bug.cgi?id=2452175
    https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-27858.json

    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