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DovecotApplication

CVE-2026-40016

MEDIUM · 6.5 CVSS v3.1 Published 2026-05-12
Fix available
A fix is available. Upgrade to 2.4.4 / 3.1.5 or later.
See remediation →
71/100
Remediation priority · Elevated
Remotely reachable 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
Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured CPU time limits for Sieve up to 130 times of the configured limit. Attacker can use this to degrade server performance and bypass configured CPU time limits for Sieve scripts. Install fixed version, or alternatively prevent direct access to Sieve scripts via ManageSieve or local access. 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

A vulnerability in Sieve script processing allows attackers to upload malicious Sieve scripts via ManageSieve service or local access that bypass configured CPU time limits by up to 130x, enabling server performance degradation.

MitigationInstall the vendor's fixed version, or restrict access to ManageSieve and local Sieve script storage to prevent unauthorized script uploads.

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:< 2.4.4
DovecotApplication
Affected:< 3.1.5

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
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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

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 installed Dovecot version
    Run 'dovecot --version' or check your package manager for the installed dovecot package version
    Affected if Version is below 2.4.4 for standard Dovecot or below 3.1.5 for Open Xchange Dovecot
  2. Verify ManageSieve protocol status
    Inspect your dovecot.conf for 'protocols' setting and look for 'managesieve' entry, or run 'doveconf -a' and search for managesieve
    Affected if ManageSieve protocol is listed as enabled in the configuration
  3. Confirm Sieve script storage is accessible
    Check for sieve script storage paths in your dovecot configuration (typically under 'sieve' or 'plugin' settings) and verify file permissions allow user access
    Affected if Sieve script storage directories exist and are writable by users who should not have admin-level access
  4. Identify existing Sieve scripts
    Locate sieve storage directories (commonly ~/sieve/ or /var/lib/dovecot/sieve/) and list all .sieve files present
    Affected if Any Sieve scripts are stored in locations accessible to non-admin users

Your environment is affected if you run a vulnerable Dovecot version with ManageSieve enabled or accessible Sieve script storage, allowing untrusted users to upload scripts that can consume excessive CPU.

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 2.4.4 / 3.1.5 or later
Fixed in 2.4.43.1.5
Interim mitigation

Install the vendor's fixed version, or restrict access to ManageSieve and local Sieve script storage to prevent unauthorized script uploads.

Recommended fix High confidence

Dovecot 2.4.4 or higher (2.x branch), or Dovecot 3.1.5 or higher (3.x branch)

  1. 1. Identify current Dovecot version: run 'dovecot --version' or check via package manager
  2. 2. Backup Dovecot configuration directory (typically /etc/dovecot/)
  3. 3. For Debian/Ubuntu: run 'apt-get update && apt-get install dovecot=1:2.4.4*' or later 2.4.x version
  4. 4. For RHEL/CentOS: run 'yum install dovecot-2.4.4*' or later 2.4.x version
  5. 5. Alternatively, obtain Dovecot 3.1.5 or later from official Dovecot repositories if using the 3.x branch
  6. 6. After installation, verify version with 'dovecot --version'
  7. 7. Restart Dovecot service: 'systemctl restart dovecot' or 'service dovecot restart'
  8. 8. Verify ManageSieve functionality is operational after upgrade
Caveat Review Dovecot release notes for your current version to target version for any configuration file or feature changes

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

Fix this in Dovecot Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing3.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,490
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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-2026-40016 in production — separate from our analysis above.

No notes yet

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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