CVE-2021-20099
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 · uneditedNessus Agent 8.2.4 and earlier for Windows were found to contain multiple local privilege escalation vulnerabilities which could allow an authenticated, local administrator to run specific Windows executables as the Nessus host. This is different than CVE-2021-20100.
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 confidenceNessus Agent 8.2.4 and earlier for Windows contains multiple local privilege escalation vulnerabilities. An authenticated local administrator can execute specific Windows executables with the privileges of the Nessus service account (the Nessus host), effectively gaining elevated local privileges.
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<= 8.2.4CVSS 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
- Local
- Complexity
- Low
- Privileges
- High
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:H/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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Verify Nessus Agent for Windows is installedOpen Services console (services.msc) and look for 'Tenable Nessus Agent' service, or check for installation at C:\Program Files\Tenable\Nessus AgentAffected if Nessus Agent for Windows is present on the system
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Determine installed Nessus Agent versionRun 'nessuscli.exe --version' from the Nessus Agent installation directory (typically C:\Program Files\Tenable\Nessus Agent), or check Programs and Features in Control Panel for the versionAffected if Version displayed is 8.2.4 or earlier
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Confirm current user has local administrator privilegesRun 'whoami /groups | find "BUILTIN\\Administrators"' from command prompt, or right-click Command Prompt and select 'Run as administrator' to test current contextAffected if Current user is a member of the local Administrators group
System is affected if Nessus Agent for Windows version 8.2.4 or earlier is installed and the checking user has local administrator privileges, which are required for the privilege escalation to be exploitable.
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 Nessus Agent for Windows to a version newer than 8.2.4. Until the upgrade is applied, limit administrative access to systems running the affected agent.
- 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-2021-20099 — 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-2021-20099 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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