CVE-2021-36809
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 · uneditedA local attacker can overwrite arbitrary files on the system with VPN client logs using administrator privileges, potentially resulting in a denial of service and data loss, in all versions of Sophos SSL VPN client.
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 confidenceThe Sophos SSL VPN client contains a local privilege escalation vulnerability where an attacker with administrator privileges can overwrite arbitrary files on the system using the VPN client logging functionality. This is likely due to insecure handling of file paths in the logging mechanism, allowing path traversal or direct file write 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 dataall versionsCVSS 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
- None
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/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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Confirm Sophos SSL VPN Client is installedCheck for the presence of Sophos SSL VPN Client software on the system. Look in Program Files for 'Sophos' or 'Sophos SSL VPN Client' folder, or query installed programs via registry (HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall) or system inventory tools.Affected if The software is present on the system - all versions are affected by this vulnerability.
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Identify the installed versionLocate the version information for the Sophos SSL VPN Client. Check the software's About dialog, look for a version file in the installation directory, or query via command line using 'wmic product where "name like '%Sophos%'" get version'.Affected if Any version is present - the advisory states all versions are affected.
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Verify the logging feature is configuredExamine the VPN client configuration for logging settings. Check the installation directory (typically C:\Program Files\Sophos\Sophos SSL VPN Client\ or similar) for log configuration files, and look for log file paths defined in the client settings or config XML files.Affected if Logging is enabled and a log file path is configured - the vulnerability exploits the logging mechanism.
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Inspect log file permissionsLocate the configured log files (typically in the client install directory or a designated log folder) and check file system permissions. Verify which users or groups have write access to these files using icacls or file properties security tab.Affected if Any user with administrator-level privileges can modify log files - the flaw allows privilege escalation via file overwrite.
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Check for suspicious log file modificationsReview recent file system events on the VPN client directory and log files. Use 'Get-ChildItem -Recurse | Where-Object { $_.LastWriteTime -gt (Get-Date).AddDays(-7) }' or check Windows Event Logs for file modification events indicating path traversal attempts or unauthorized file writes.Affected if Log files or unrelated files in the system have been modified, especially from the VPN client process context.
If Sophos SSL VPN Client is installed with logging enabled, the environment is affected since all versions contain this privilege escalation vulnerability in the logging functionality.
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 dataApply vendor-supplied patches for Sophos SSL VPN client when available. In the interim, restrict administrative privileges on endpoints running the VPN client and monitor for suspicious file modification activities.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2021-36809 — 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-2021-36809 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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