CVE-2023-21555
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 confidenceThis is a remote code execution vulnerability in Windows Layer 2 Tunneling Protocol (L2TP), a widely-used VPN tunneling protocol. The vulnerability allows an unauthenticated attacker to execute arbitrary code on affected Windows systems by sending specially crafted L2TP packets, likely through a buffer overflow or similar memory corruption flaw in the L2TP implementation.
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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Check Windows versionRun 'winver' or 'systeminfo | findstr /B /C:"OS Name" /C:"OS Version"' to identify the Windows version and buildAffected if The version is Windows 10 1607, 1809, 20H2, 21H2, 22H2, Windows 11 21H2, 22H2, or Windows 7 (any build)
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Verify L2TP is configuredCheck for L2TP VPN connections or RAS ports. Run 'Get-VpnConnection -AllUserConnection' in PowerShell or check for L2TP-type RAS ports via 'netsh ras dump'Affected if Any L2TP-based VPN connection exists or L2TP ports (UDP 1701) are configured
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Check if L2TP service is enabledRun 'Get-Service RemoteAccess' in PowerShell or check via Services.msc to see if Routing and Remote Access (RRAS) is runningAffected if Routing and Remote Access service is enabled and L2TP is in use
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Verify security update is installedRun 'Get-HotFix | Where-Object {$_.Description -eq "Security Update"} | Select-Object HotFixID, InstalledOn' to list installed security updates, or check Windows Update historyAffected if No Microsoft security update for CVE-2023-21555 is installed (patch date around January 2023)
You are affected if you run any of the listed Windows versions with L2TP VPN functionality enabled and the CVE-2023-21555 security update has not been installed.
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 · scopedApply the relevant Microsoft security updates for this vulnerability (typically through Windows Update or WSUS) and verify L2TP VPN functionality continues to work correctly after patching.
- Enable automatic Windows Updates or check for updates manually via Settings > Update & Security > Windows Update
- Install the latest security update for this vulnerability (KB number varies by Windows version - check Microsoft Security Response Center for the specific KB for your Windows version)
- Restart the system after installing the update if prompted
- Verify the update was installed successfully by checking the installed updates list
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation3.0 h
- Implementation2.0 h
- Testing4.0 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 $3,072.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2023-21555 — 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-2023-21555 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