CVE-2026-33603
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 · uneditedAttacker can use a specially crafted base64 exchange between Dovecot and Client to fake SCRAM TLS channel binding. This requires that the attacker is able to position itself between Dovecot and the client connection. If successful, the attacker can eavesdrop communications between Dovecot and client as MITM proxy. 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 confidenceA vulnerability in Dovecot allows an attacker positioned as a man-in-the-middle to craft a malicious base64 exchange that fakes SCRAM TLS channel binding, enabling eavesdropping on communications between Dovecot and clients.
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< 2.4.4< 3.1.5CVSS 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
- Adjacent
- Complexity
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:A/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.
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Check installed Dovecot versionRun `dovecot --version` or use your package manager to query the installed dovecot package version (e.g., `rpm -q dovecot` or `dpkg -l dovecot`)Affected if The version number is less than 2.4.4 (for Dovecot) or less than 3.1.5 (for Open Xchange Dovecot)
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Verify SCRAM authentication mechanism is enabledRun `dovecot -n` and look for the `auth_mechanisms` setting in the output. Common config file location is /etc/dovecot/dovecot.confAffected if The auth_mechanisms line includes SCRAM-SHA-1, SCRAM-SHA-256, or SCRAM (any SCRAM variant)
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Confirm TLS/SSL is enabled for connectionsCheck the dovecot configuration for `ssl = yes` or `ssl required` settings, and verify that imaps (993) and/or pop3s (995) or submission (587) with TLS are configuredAffected if SSL/TLS is enabled (the vulnerability exploits TLS channel binding in SCRAM, so TLS must be active for exploitation)
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Review authentication logs for unusual SCRAM exchangesExamine Dovecot auth logs (typically in /var/log/dovecot.log or /var/log/mail.log) for any SCRAM authentication failures, unexpected base64 strings, or channel binding errorsAffected if Multiple failed SCRAM auth attempts with malformed base64 data are observed, which may indicate exploitation attempts
You are affected if Dovecot version is below the fixed versions AND SCRAM authentication with TLS is enabled, allowing a network attacker to manipulate the SCRAM TLS channel binding exchange.
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 · scoped2.4.43.1.5
Upgrade Dovecot to the vendor-provided fixed version that addresses the SCRAM TLS channel binding manipulation.
Dovecot 2.4.4 (for 2.x line) or Dovecot 3.1.5 (for 3.x line)
- 1. Identify your current Dovecot installation version using: dovecot --version
- 2. Backup your current Dovecot configuration directory (typically /etc/dovecot/)
- 3. For Dovecot 2.x users: Upgrade to version 2.4.4 or later
- 4. For Dovecot 3.x users: Upgrade to version 3.1.5 or later
- 5. After installation, restart the Dovecot service: systemctl restart dovecot (or your system's service manager)
- 6. Verify the upgrade was successful and the service is running: dovecot --version
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-33603 — 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-2026-33603 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
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- Version or environment caveats, and links to real fixes
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