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DovecotApplication

CVE-2026-24031

HIGH · 8.2 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 →
91/100
Remediation priority · Urgent
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
Dovecot SQL based authentication can be bypassed when auth_username_chars is cleared by admin. This vulnerability allows bypassing authentication for any user and user enumeration. Do not clear auth_username_chars. If this is not possible, install latest 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 · high confidence

Dovecot's SQL-based authentication can be bypassed when the auth_username_chars configuration directive is cleared (emptied) by an administrator. This allows attackers to bypass authentication entirely for any user account and perform user enumeration to discover valid usernames in the system.

MitigationEnsure auth_username_chars is properly configured with valid character sets and never left empty; if this cannot be done, upgrade to the latest Dovecot version containing the security fix.

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
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/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 'doveadm version' or 'dovecot --version' to determine the installed version
    Affected if Version is below 2.4.3 for Dovecot or below 3.1.4 for Open Xchange Dovecot
  2. Locate Dovecot configuration
    Common locations are /etc/dovecot.conf, /etc/dovecot/conf.d/, or /usr/local/etc/dovecot.conf. Check dovecot -n for the actual config path
    Affected if Configuration file found with auth_username_chars setting present but empty
  3. Verify auth_username_chars setting
    Search config files for 'auth_username_chars' using grep. Check if it appears as 'auth_username_chars = ' with nothing after the equals sign, or is commented out (defaulting to empty in some contexts)
    Affected if auth_username_chars is set to empty string or not explicitly defined and relying on default behavior that allows empty value
  4. Confirm SQL authentication is in use
    Check for 'passdb sql' or 'userdb sql' in the Dovecot configuration to confirm SQL-based authentication is enabled
    Affected if SQL passdb or userdb is configured AND auth_username_chars is empty

If running an affected version of Dovecot with SQL authentication AND the auth_username_chars configuration option is set to empty or not properly defined, the environment is vulnerable to authentication bypass.

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 properly configured with valid character sets and never left empty; if this cannot be done, upgrade to the latest Dovecot version containing the security fix.

Recommended fix High confidence

Dovecot >= 2.4.3 or Dovecot >= 3.1.4

  1. 1. Locate the Dovecot configuration file (typically /etc/dovecot/conf.d/ or /etc/dovecot/dovecot.conf)
  2. 2. Search for the auth_username_chars setting in the configuration
  3. 3. Ensure auth_username_chars is NOT cleared or left empty - it should contain a valid character set (e.g., auth_username_chars = @abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789.-_@)
  4. 4. If auth_username_chars was previously cleared, restore it to the default or a custom valid character set
  5. 5. Restart the Dovecot service to apply changes (e.g., systemctl restart dovecot)
  6. 6. Alternatively, if the configuration change is not feasible, upgrade Dovecot to version 2.4.3 or later for the 2.x branch, or 3.1.4 or later for the 3.x branch
Caveat Minor - upgrading Dovecot may require testing of existing mail configurations and plugins, but the vendor considers this safe to apply

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

Fix this in Dovecot Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing2.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,420
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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-2026-24031 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