CVE-2021-35223
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 · uneditedThe Serv-U File Server allows for events such as user login failures to be audited by executing a command. This command can be supplied with parameters that can take the form of user string variables, allowing remote code execution.
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 confidenceServ-U File Server contains a command injection vulnerability in its audit feature. When auditing events such as user login failures, the server executes configured commands with parameters that can include user string variables. By supplying specially crafted input as user variables during failed login attempts, remote attackers can achieve arbitrary command execution on the host.
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< 15.2.4CVSS 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
- 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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Check Serv-U versionOpen Serv-U Administration console and go to Help > About, or run 'ServUAdmin.exe -version' from the installation directoryAffected if Version is lower than 15.2.4
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Verify audit command execution feature is configuredIn Serv-U console, navigate to Security & Authentication > Audit or Settings > Audit. Look for any configured external commands that execute on events such as login failuresAffected if An audit command (script or executable) is configured to run on audit events like user login failures
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Confirm audit command uses user-supplied variablesIn the audit command configuration, examine if the command path or parameters include user variables such as username, user input strings, or session variables that could be manipulatedAffected if The configured audit command incorporates user-supplied variables in its execution path or arguments
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Assess management interface exposureCheck firewall rules and network configuration to determine if the Serv-U administration interface (typically ports 80, 443, or custom admin ports) is accessible from untrusted networks or the internetAffected if The Serv-U management or FTP interface is exposed to untrusted networks without adequate access controls
A user is affected if running Serv-U version below 15.2.4 with an audit command configured that processes user variables, and the interface is network-accessible to remote attackers.
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 · scoped15.2.4
Update Serv-U File Server to the vendor-patched version. If immediate patching is not feasible, disable the audit command execution feature or restrict network access to the management interface to mitigate remote exploitation.
Serv-U 15.2.4 or later
- Upgrade Serv-U File Server to version 15.2.4 or later
- After upgrading, verify the installation by checking the Serv-U version in the administration console
- Test that the event auditing functionality works correctly with the updated version
- Ensure that any custom event audit commands are reviewed for proper input validation
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation3.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,408.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-35223 — 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-2021-35223 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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