Openvpn Access ServerApplication · Openvpn
CVE-2021-4234
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 · uneditedOpenVPN Access Server 2.10 and prior versions are susceptible to resending multiple packets in a response to a reset packet sent from the client which the client again does not respond to, resulting in a limited amplification attack.
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 · moderate confidenceOpenVPN Access Server 2.10 and prior contains an amplification vulnerability where the server repeatedly resends multiple packets in response to a reset packet from a client. Since the client does not respond to these retransmissions, an attacker can exploit this to cause a limited amplification DoS attack.
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
Openvpn Access ServerApplication
< 2.11.0CVSS 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
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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 installed OpenVPN Access Server versionRun the command 'openvpn-as --version' or 'openvpn --version' from the server command line to retrieve the installed version numberAffected if The version displayed is less than 2.11.0 (for example, 2.10.x, 2.9.x, or earlier)
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Verify OpenVPN Access Server package versionIf the above command is unavailable, check the installed package version using your system's package manager (for example, 'rpm -qa | grep openvpn-as' on RHEL/CentOS or 'dpkg -l | grep openvpn-as' on Debian/Ubuntu)Affected if The package version listed is below 2.11.0
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Confirm the service is runningCheck that the OpenVPN Access Server service is active and running using 'systemctl status openvpnas' or 'service openvpn-as status'Affected if The service is active and the version from step 1 or 2 is below 2.11.0
You are affected if the installed OpenVPN Access Server version is any release prior to 2.11.0, as this is where the amplification vulnerability in the packet retransmission logic was addressed.
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 · scoped2.11.0
Update OpenVPN Access Server to a version beyond 2.10. Consider implementing network-level rate limiting or traffic filtering as an additional safeguard until the patch is applied.
2.11.0
- Backup the current OpenVPN Access Server configuration before proceeding with the upgrade
- Download and install OpenVPN Access Server version 2.11.0 or later from the official OpenVPN website (openvpn.net) or your distribution's package repository
- Run the 'openvpnas' upgrade script or use the appropriate package manager to complete the upgrade
- Verify the upgrade was successful by checking the Access Server version in the admin web interface or via command line
- Ensure the OpenVPN Access Server service is running properly after the upgrade
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Openvpn Access Server
Scoped from the published advisory
- Consultation2.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,984.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-4234 — 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-2021-4234 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
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