Linux KernelOperating system · Linux
CVE-2009-3623
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 · uneditedThe lookup_cb_cred function in fs/nfsd/nfs4callback.c in the nfsd4 subsystem in the Linux kernel before 2.6.31.2 attempts to access a credentials cache even when a client specifies the AUTH_NULL authentication flavor, which allows remote attackers to cause a denial of service (NULL pointer dereference and system crash) via an NFSv4 mount request.
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 confidenceThe lookup_cb_cred function in the Linux kernel's NFSv4 callback handler attempts to access a credentials cache even when a client specifies AUTH_NULL authentication. Since no valid credentials exist for AUTH_NULL, this triggers a NULL pointer dereference, causing a kernel panic and system crash when processing malicious NFSv4 mount requests.
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
Linux KernelOperating system
<= 2.6.31.1= 2.6.0= 2.6.1= 2.6.2= 2.6.3= 2.6.4= 2.6.5= 2.6.6= 2.6.7= 2.6.8= 2.6.8.1= 2.6.9CVSS 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
- Authentication
- None
- Confidentiality
- None
- Integrity
- None
- Availability
- Complete
AV:N/AC:L/Au:N/C:N/I:N/A:C
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 the running kernel versionRun 'uname -r' or 'cat /proc/version' to obtain the exact kernel versionAffected if The kernel version is 2.6.31.1 or earlier, or matches any of the specific affected versions 2.6.0 through 2.6.9.x
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Determine if NFSv4 server support is enabledCheck /proc/filesystems for nfsv4 entries, or run 'lsmod | grep nfs' to see loaded NFS modules, or check /etc/exports for NFSv4 exportsAffected if NFSv4 server exports exist in /etc/exports or the nfsd module is loaded
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Verify if the system is configured as an NFS serverRun 'rpcinfo -p' or check if the nfsd service is running ('systemctl status nfs-server' or 'service nfs status')Affected if The NFS server daemon (nfsd) is running and listening for mount requests
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Confirm NFSv4 callback handler is activeCheck if the rpc.idmapd or other NFSv4-related daemons are running, and verify RPC ports 2049/TCP are openAffected if The system accepts NFSv4 mount connections from network clients
A system is affected if it runs a vulnerable kernel version (2.6.31.1 or earlier, or 2.6.0-2.6.9.x) AND serves NFSv4 exports to network clients, allowing remote attackers to trigger the NULL pointer dereference via malicious mount requests.
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 upstream kernel patch (or upgrade to Linux kernel 2.6.31.2 or later). For systems that cannot be immediately patched, consider restricting NFSv4 mount access via firewall rules or network segmentation to limit exposure to untrusted clients.
Fix this in Linux Kernel
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing8.0 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 $6,656.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2009-3623 — 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-2009-3623 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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- Version or environment caveats, and links to real fixes
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