CVE-2019-5456
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 · uneditedSMTP MITM refers to a malicious actor setting up an SMTP proxy server between the UniFi Controller version <= 5.10.21 and their actual SMTP server to record their SMTP credentials for malicious use later.
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 confidenceUniFi Controller versions 5.10.21 and earlier are vulnerable to an SMTP man-in-the-middle attack where a malicious actor intercepts SMTP credentials by positioning a proxy server between the controller and the legitimate SMTP server, allowing credential theft for subsequent malicious use.
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<= 5.10.21CVSS 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
- High
- Availability
- High
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/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 checksWork through these to decide whether this CVE applies to you.
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Determine UniFi Controller versionAccess the UniFi Controller web interface and navigate to the settings or about page to view the controller version. Alternatively, check the controller's system information or log files for the version number.Affected if The installed version is 5.10.21 or earlier
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Verify SMTP configuration existsIn the UniFi Controller settings, locate the SMTP or email notification configuration section. Check if SMTP settings are configured and enabled for sending notifications or alerts.Affected if SMTP is configured and enabled in the controller
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Check SMTP encryption settingsIn the SMTP configuration section, inspect the security or encryption settings for the SMTP connection. Verify whether TLS, SSL, or STARTTLS is enabled for the SMTP connection.Affected if SMTP is configured without TLS/SSL encryption (plaintext connection)
You are affected if your UniFi Controller version is 5.10.21 or earlier AND SMTP is configured without encryption, as this allows credential interception via a man-in-the-middle attack.
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.
From vendor dataUpgrade UniFi Controller to a version beyond 5.10.21. Additionally, ensure SMTP connections use TLS/SSL encryption to prevent credential interception in transit.
- Consultation2.0 h
- Implementation1.0 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-2019-5456 — 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-2019-5456 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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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