CVE-2021-20076
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 · uneditedTenable.sc and Tenable.sc Core versions 5.13.0 through 5.17.0 were found to contain a vulnerability that could allow an authenticated, unprivileged user to perform Remote Code Execution (RCE) on the Tenable.sc server via Hypertext Preprocessor unserialization.
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 confidencePHP unserialize vulnerability in Tenable.sc and Tenable.sc Core versions 5.13.0 through 5.17.0 allows an authenticated but unprivileged user to achieve remote code execution on the server through malicious PHP deserialization.
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>= 5.13.0, <= 5.17.0CVSS 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
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:L/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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Identify the installed Tenable.sc product and versionAccess the Tenable.sc web interface and navigate to the 'System' > 'About' page, or use the API endpoint '/rest/status' to retrieve the version informationAffected if The product is Tenable.sc or Tenable.sc Core and the version is 5.13.0, 5.14.0, 5.15.0, 5.16.0, 5.17.0, or any version within the range 5.13.0 to 5.17.0 inclusive
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Confirm the exact version number against the affected rangeCompare the retrieved version to the known vulnerable range: version must be greater than or equal to 5.13.0 AND less than or equal to 5.17.0Affected if The installed version falls within 5.13.0 <= version <= 5.17.0, indicating the vulnerable PHP unserialize code path exists in this release
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Verify if user authentication is enabled on the systemCheck the Tenable.sc authentication settings through the web UI under 'Users' and 'Authentication' sections, or attempt to access a protected API endpoint to confirm authentication is requiredAffected if User authentication is enabled and any user account can be created or exists, because the vulnerability requires an authenticated (but unprivileged) user to trigger the PHP deserialization
If Tenable.sc or Tenable.sc Core is installed with a version between 5.13.0 and 5.17.0 inclusive and user authentication is enabled, the environment is affected by CVE-2021-20076.
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 Tenable.sc/Tenable.sc Core to version 5.18.0 or later, which contains the vendor patch addressing this vulnerability.
- Consultation2.0 h
- Implementation4.0 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-2021-20076 — 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-2021-20076 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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- 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
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