CVE-2023-21679
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 · uneditedWindows Layer 2 Tunneling Protocol (L2TP) Remote Code Execution Vulnerability
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 confidenceWindows L2TP Remote Code Execution Vulnerability - A remote code execution vulnerability exists in the Windows Layer 2 Tunneling Protocol (L2TP) implementation. An attacker could exploit this by sending specially crafted packets to a target system running L2TP services, potentially allowing arbitrary code execution with elevated 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 dataall versionsall versionsall versionsall versionsall versionsall versionsall versionsall 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
- Network
- Complexity
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:H/PR:N/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 Windows versionRun 'winver' or 'systeminfo | findstr /B /C:"OS Name" /C:"OS Version"' to determine the installed Windows version and build number.Affected if The version matches any of these affected releases: Windows 10 1607, 1809, 20h2, 21h2, 22h2; Windows 11 21h2, 22h2; or Windows 7 (any version).
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Check for L2TP VPN connectionsOpen Control Panel > Network and Sharing Center > Set up a new connection or network. Look for any VPN connections configured with L2TP/IPsec. Alternatively, check the file %APPDATA%\Microsoft\Network\Connections\rasphone.pbk for L2TP entries.Affected if Any L2TP-based VPN connection profile exists on the system.
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Check Routing and Remote Access serviceRun 'services.msc' and locate the 'Routing and Remote Access' (RRAS) service. Check its status and configuration, or run 'netsh routing ip status' if available.Affected if RRAS service is running and configured with L2TP VPN or demand-dial interfaces.
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Verify L2TP listener portsRun 'netsh interface portproxy show all' or check listening ports with 'netstat -an | findstr ":1701"' - UDP port 1701 is used by L2TP.Affected if The system is listening on UDP port 1701 (L2TP).
A system is affected if it runs an affected Windows version AND has L2TP enabled (either via a configured VPN connection, RRAS service, or listening on L2TP ports).
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 the Microsoft security update for CVE-2023-21679 to all affected Windows systems. Prioritize servers and systems with L2TP VPN functionality exposed to untrusted networks.
- Consultation1.0 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 $1,664.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2023-21679 — 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-2023-21679 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
- No spam, self-promotion, credentials, or personal data