Layer 2 Tunneling ProtocolApplication · Linux
CVE-2022-4129
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 · uneditedA flaw was found in the Linux kernel's Layer 2 Tunneling Protocol (L2TP). A missing lock when clearing sk_user_data can lead to a race condition and NULL pointer dereference. A local user could use this flaw to potentially crash the system causing a denial of service.
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 confidenceA race condition exists in the Linux kernel's L2TP implementation where clearing sk_user_data lacks proper locking. This allows a local attacker to trigger a NULL pointer dereference by exploiting the race window, potentially crashing the system.
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
Layer 2 Tunneling ProtocolApplication
< 6.0
FedoraOperating system
= 35= 36= 37CVSS 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
- Local
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:L/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 the running kernel versionRun 'uname -r' or 'uname -a' to see the kernel version numberAffected if The kernel version is 5.x or earlier (versions below 6.0)
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Verify if L2TP kernel modules are loadedRun 'lsmod | grep l2tp' to list loaded L2TP-related modulesAffected if Any L2TP modules (l2tp_netlink, l2tp_core, l2tp_eth, pppol2tp, etc.) appear in the loaded module list
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Check if L2TP is actively configured or in useInspect /proc/net/pppol2tp or run 'ip l2tp show' to see if any L2TP tunnels or sessions existAffected if L2TP tunnels or sessions are actively established
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Check L2TP module availabilityRun 'modinfo l2tp_core 2>/dev/null' to verify the L2TP module exists on the systemAffected if The L2TP kernel module is present on the system
A system is affected if it runs a kernel version below 6.0 AND has L2TP kernel modules loaded or L2TP tunnels actively in use, as the race condition only triggers when L2TP is enabled and operational.
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 · scoped6.0
Apply the kernel security update that adds proper locking around sk_user_data operations in the L2TP code. For systems that cannot immediately update, consider restricting local user access or disabling L2TP if not required.
Linux kernel >= 6.0 or distribution-specific kernel update
- Update the Linux kernel to version 6.0 or later which contains the fix for the L2TP sk_user_data race condition
- For Fedora systems (35, 36, 37), run: sudo dnf update kernel
- Reboot the system to load the new kernel
- Verify the running kernel version with: uname -r
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Layer 2 Tunneling Protocol
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing12.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $7,616.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2022-4129 — 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-2022-4129 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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