CVE-2026-27856
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 · uneditedDoveadm credentials are verified using direct comparison which is susceptible to timing oracle attack. An attacker can use this to determine the configured credentials. Figuring out the credential will lead into full access to the affected component. Limit access to the doveadm http service port, 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 confidenceDovecot's doveadm service uses a direct string comparison for credential verification, creating a timing oracle that allows attackers to infer credentials character-by-character by measuring response times. This timing side-channel enables precise credential extraction leading to full administrative access.
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< 2.4.3< 2.3.22.1>= 3.0.0, < 3.0.5>= 3.1.0, < 3.1.4CVSS 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
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/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 checksWork through these to decide whether this CVE applies to you.
-
Identify installed Dovecot versionRun 'dovecot --version' or check via package manager (rpm -q dovecot, dpkg -l dovecot)Affected if Version is below 2.4.3 for Dovecot, below 2.3.22.1 for OX Dovecot, between 3.0.0-3.0.5, or between 3.1.0-3.1.4 for OX Dovecot
-
Verify doveadm HTTP service is enabledCheck dovecot configuration files (dovecot.conf, doveadm.conf) for 'service doveadm' block with 'http' listener, or run 'doveadm who' to see if service respondsAffected if doveadm HTTP service is configured and enabled
-
Confirm doveadm HTTP port is network-exposedRun 'ss -tlnp | grep doveadm' or 'netstat -tlnp | grep doveadm' to see listening ports; examine 'listen' directive in doveadm.confAffected if Port 8080 or configured doveadm HTTP port is bound to 0.0.0.0 or accessible from network interfaces rather than localhost only
-
Test doveadm HTTP interface accessibilityAttempt local HTTP request: 'curl -k http://localhost:8080/doveadm' (adjust port if different); check if authentication prompt appearsAffected if doveadm HTTP endpoint responds to network requests without authentication first
-
Review doveadm authentication configurationExamine dovecot configuration for 'doveadm_password' or 'doveadm_username' settings in dovecot.conf or password filesAffected if doveadm authentication is configured (the timing oracle only matters if credentials are set)
User is affected if running an affected Dovecot/OX Dovecot version AND doveadm HTTP service is enabled and network-accessible, allowing remote attackers to perform timing-based credential inference.
Generated from the published advisory. Verify against your own configuration.
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 · scoped2.3.22.12.4.33.0.5
Restrict network access to the doveadm HTTP port using firewall rules or network segmentation, and upgrade to the patched Dovecot version that implements constant-time comparison.
Dovecot 2.3.22.1+ (2.3.x), 2.4.3+ (2.4.x), 3.0.5+ (3.0.x), or 3.1.4+ (3.1.x) depending on your current branch
- 1. Identify the current Dovecot version installed (e.g., doveadm --version or dovecot --version)
- 2. Determine which version branch is currently in use (2.3.x, 2.4.x, 3.0.x, or 3.1.x)
- 3. Upgrade to the fixed version for that branch: 2.3.22.1 or later, 2.4.3 or later, 3.0.5 or later, or 3.1.4 or later
- 4. After upgrading, verify the new version is installed correctly
- 5. As an additional mitigation, restrict network access to the doveadm HTTP service port (default 8080) using firewall rules or network segmentation
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation3.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,408.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-27856 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-27856 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
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.
- 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