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DovecotApplication

CVE-2026-27857

HIGH · 7.5 CVSS v3.1 Published 2026-03-27
Fix available
A fix is available. Upgrade to 2.3.22.1 / 2.4.3 or later.
See remediation →
84/100
Remediation priority · High
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
Sending "NOOP (((...)))" command with 4000 parenthesis open+close results in ~1MB extra memory usage. Longer commands will result in client disconnection. This 1 MB can be left allocated for longer time periods by not sending the command ending LF. So attacker could connect possibly from even a single IP and create 1000 connections to allocate 1 GB of memory, which would likely result in reaching VSZ limit and killing the process and its other proxied connections. Attacker could connect possibly from even a single IP and create 1000 connections to allocate 1 GB of memory, which would likely result in reaching VSZ limit and killing the process and its other proxied connections. Install fixed version, there is no other remediation. 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

A memory allocation vulnerability exists in the NOOP command handler where sending a command with 4000 or more parenthesis characters (open and close) causes approximately 1MB of extra memory to be allocated per connection. By not sending the command-ending LF (line feed), this memory remains allocated for extended periods, enabling a single attacker from one IP to create 1000 connections and allocate 1GB of memory, exhausting the VSZ limit and causing process termination with loss of all proxied connections.

MitigationInstall the vendor-provided fixed version. No workaround or alternative mitigation exists per the vendor; this is a canonical fix-required vulnerability.

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:< 2.3.22.1>= 3.0.0, < 3.0.5>= 3.1.0, < 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
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/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. Identify installed Dovecot version
    Run 'dovecot --version' or check the package manager (e.g., 'rpm -q dovecot' or 'dpkg -l dovecot')
    Affected if The installed version is below 2.4.3, or below 2.3.22.1, or between 3.0.0-3.0.5, or between 3.1.0-3.1.4 for Open Xchange variants
  2. Verify IMAP or POP3 service is exposed
    Check listening ports with 'netstat -tlnp | grep -E ':(143|110|993|995)' or review dovecot configuration files for enabled protocols
    Affected if IMAP (143/993) or POP3 (110/995) listeners are active and accessible from network interfaces
  3. Check for untrusted network access
    Review firewall rules or dovecot configuration (disable_plaintext_auth, ssl, login_trusted_networks) to determine if IMAP/POP3 is reachable from untrusted networks
    Affected if The IMAP or POP3 service accepts connections from IP addresses that are not fully trusted (e.g., internet-facing)
  4. Monitor connection memory consumption
    Observe process memory usage of dovecot/imap-login processes during active client connections, particularly from any suspicious sources
    Affected if Memory usage grows significantly per connection and does not release after commands complete (requires process inspection during an active attack)
  5. Review connection state and resource limits
    Check dovecot configuration for connection limits (mail_max_connections, default_process_limit) and observe established connections via 'netstat' or 'ss'
    Affected if High numbers of concurrent connections can be established from single IPs without triggering rate limiting

You are affected if you run a vulnerable Dovecot version (less than 2.4.3 or the Open Xchange versions listed) with IMAP or POP3 services exposed to untrusted networks, allowing attackers to trigger memory exhaustion through malformed NOOP commands.

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 2.3.22.1 / 2.4.3 / 3.0.5 or later
Fixed in 2.3.22.12.4.33.0.5
Interim mitigation

Install the vendor-provided fixed version. No workaround or alternative mitigation exists per the vendor; this is a canonical fix-required vulnerability.

Recommended fix High confidence

Dovecot 2.4.3 (2.x branch), 2.3.22.1 (legacy 2.x), 3.0.5 (3.0.x), or 3.1.4 (3.1.x) - minimum version depends on your current branch

  1. Identify currently installed Dovecot version using 'dovecot --version'
  2. For Dovecot 2.x versions < 2.3.22.1: upgrade to version 2.3.22.1 or later
  3. For Dovecot 2.x versions < 2.4.3: upgrade to version 2.4.3 or later (preferred for 2.x)
  4. For Dovecot 3.0.x versions < 3.0.5: upgrade to version 3.0.5 or later
  5. For Dovecot 3.1.x versions < 3.1.4: upgrade to version 3.1.4 or later
  6. Use package manager (apt/yum/dnf) or Dovecot repository to install the fixed version
  7. After installation, restart Dovecot service: 'systemctl restart dovecot' or 'service dovecot restart'
  8. Verify service is running: 'systemctl status dovecot'

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

Fix this in Dovecot Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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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-2026-27857 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