dbcve.org
Windows 10Operating system · Microsoft

CVE-2023-21757

HIGH · 7.5 CVSS v3.1 Published 2023-01-10
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

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 · unedited
Windows Layer 2 Tunneling Protocol (L2TP) Denial of Service 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 · low confidence

A denial of service vulnerability exists in Windows Layer 2 Tunneling Protocol (L2TP) implementation. An unauthenticated remote attacker could send specially crafted packets to cause the L2TP service to become unresponsive, disrupting VPN connectivity.

MitigationApply the Microsoft security update for CVE-2023-21757. If immediate patching is not feasible, consider firewall rules to limit L2TP exposure to trusted networks or disable L2TP if not required.

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
Windows 10Operating system
Affected:all versions= 20h2= 21h2= 22h2= 1607= 1809
Windows 11Operating system
Affected:all versions= 21h2= 22h2
Windows 7Operating system
Affected:all versions
Windows 8.1Operating system
Affected:all versions
Windows Rt 8.1Operating system
Affected:all versions
Windows Server 2008Operating system
Affected:all versions= r2
Windows Server 2012Operating system
Affected:all versions= r2
Windows Server 2016Operating system
Affected:all versions

CVSS 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 checks

Work through these to decide whether this CVE applies to you.

  1. Check Windows version
    Run 'winver' or 'systeminfo | findstr /B /C:"OS Name" /C:"OS Version"' to identify the exact Windows version and build number
    Affected if The version is NOT listed in CVE-2023-21757 affected products (Windows 10 versions prior to patches, Windows 11 prior to patches, Windows 7, 8.1, Rt 8.1, Server 2008, Server 2012, Server 2016)
  2. Verify L2TP/IPsec is enabled
    Check the routing and remote access (RRAS) configuration: open 'ncpa.cpl', right-click your network adapter, select Properties, and look for 'Layer 2 Tunneling Protocol (L2TP)' in the list
    Affected if L2TP protocol is checked/enabled in network adapter settings or RRAS configuration
  3. Confirm L2TP service status
    Run 'Get-Service RemoteAccess' in PowerShell or check Services.msc for 'Routing and Remote Access (RRAS)' service status
    Affected if The RemoteAccess service is running or set to Automatic start
  4. Detect listening L2TP ports
    Run 'netstat -ano | findstr "1701 500 4500"' to check if L2TP/IPsec ports (UDP 1701 for L2TP, UDP 500 for IKE, UDP 4500 for NAT-T) are listening
    Affected if Any of these UDP ports are in LISTENING or ESTABLISHED state, indicating active L2TP/IPsec

A system is likely affected if it runs a vulnerable Windows version from the affected list AND has L2TP protocol enabled or the RemoteAccess service running and listening on L2TP ports.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the Microsoft security update for CVE-2023-21757. If immediate patching is not feasible, consider firewall rules to limit L2TP exposure to trusted networks or disable L2TP if not required.

Recommended fix High confidence
  1. Open Windows Update on the affected system (Settings > Update & Security > Windows Update)
  2. Click 'Check for updates' to download and install the January 2023 security updates
  3. Alternatively, download the appropriate security update from the Microsoft Update Catalog for your specific Windows version
  4. Restart the system after the update is installed
  5. Verify the update was installed by checking installed updates (run 'appwiz.cpl' and view installed updates)

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Windows 10 Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,328.

Scan for this in your stack

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dbcve dependency scanner

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2023-21757 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

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.

What belongs here
  • 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