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DovecotApplication

CVE-2026-27860

MEDIUM · 5.3 CVSS v3.1 Published 2026-03-27
Fix available
A fix is available. Upgrade to 2.4.3 / 3.1.4 or later.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
If auth_username_chars is empty, it is possible to inject arbitrary LDAP filter to Dovecot's LDAP authentication. This leads to potentially bypassing restrictions and allows probing of LDAP structure. Do not clear out auth_username_chars, or install fixed version. No publicly available exploits are known.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

When the Dovecot configuration parameter auth_username_chars is set to an empty value, it allows LDAP filter injection during the authentication process. An attacker can manipulate the username input to inject arbitrary LDAP filters, potentially bypassing authentication restrictions and enumerating LDAP directory structure information.

MitigationEnsure auth_username_chars is not left empty in Dovecot configuration; set it to a valid character set (default is typically '%u' or a character class), or upgrade to the fixed Dovecot version.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
DovecotApplication
Affected:< 2.4.3
DovecotApplication
Affected:< 3.1.4

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check Dovecot version
    Run 'dovecot --version' or check the installed package version using your system's package manager
    Affected if The installed version is below 2.4.3 for standard Dovecot or below 3.1.4 for Open Xchange Dovecot
  2. Confirm LDAP authentication is in use
    Inspect Dovecot configuration files (typically in /etc/dovecot/ or /usr/local/etc/dovecot/) for 'userdb ldap' or 'passdb ldap' directives in dovecot.conf or conf.d/ directories
    Affected if LDAP user or password databases are configured, as this vulnerability only affects LDAP authentication
  3. Inspect auth_username_chars setting
    Search for 'auth_username_chars' in Dovecot configuration files. Common locations include dovecot.conf, dovecot-ldap.conf, or files in conf.d/ directory. Use grep: 'grep -r auth_username_chars /etc/dovecot/'
    Affected if The parameter is set to an empty value (auth_username_chars = "" with nothing between the quotes), which enables the injection vector

You are affected if your Dovecot version is vulnerable, LDAP authentication is configured, AND auth_username_chars is set to an empty value, allowing LDAP filter injection via username manipulation.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 2.4.3 / 3.1.4 or later
Fixed in 2.4.33.1.4
Interim mitigation

Ensure auth_username_chars is not left empty in Dovecot configuration; set it to a valid character set (default is typically '%u' or a character class), or upgrade to the fixed Dovecot version.

Recommended fix Moderate confidence

Dovecot 2.4.3 (for 2.x line) or Dovecot 3.1.4 (for 3.x line)

  1. 1. Identify current Dovecot version by running: dovecot --version
  2. 2. For Dovecot 2.x: Upgrade to version 2.4.3 or later
  3. 3. For Dovecot 3.x: Upgrade to version 3.1.4 or later
  4. 4. After upgrade, verify auth_username_chars is set in /etc/dovecot/conf.d/10-auth.conf or dovecot.conf
  5. 5. Ensure auth_username_chars contains valid characters (e.g., auth_username_chars = @abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789.-_@)
  6. 6. Reload or restart Dovecot service: systemctl reload dovecot or systemctl restart dovecot
  7. 7. Test authentication to ensure proper functionality
Caveat Minor patch upgrades typically have minimal breaking changes; review release notes for any auth-related changes

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Dovecot Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing3.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,210
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-27860 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data