Linux KernelOperating system · Linux
CVE-2026-52999
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 · uneditedIn the Linux kernel, the following vulnerability has been resolved: netfilter: nfnetlink_osf: fix out-of-bounds read on option matching In nf_osf_match(), the nf_osf_hdr_ctx structure is initialized once and passed by reference to nf_osf_match_one() for each fingerprint checked. During TCP option parsing, nf_osf_match_one() advances the shared ctx->optp pointer. If a fingerprint perfectly matches, the function returns early without restoring ctx->optp to its initial state. If the user has configured NF_OSF_LOGLEVEL_ALL, the loop continues to the next fingerprint. However, because ctx->optp was not restored, the next call to nf_osf_match_one() starts parsing from the end of the options buffer. This causes subsequent matches to read garbage data and fail immediately, making it impossible to log more than one match or logging incorrect matches. Instead of using a shared ctx->optp pointer, pass the context as a constant pointer and use a local pointer (optp) for TCP option traversal. This makes nf_osf_match_one() strictly stateless from the caller's perspective, ensuring every fingerprint check starts at the correct option offset.
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 logic error in Linux kernel's netfilter OS fingerprinting module causes an out-of-bounds read vulnerability. The ctx->optp pointer is advanced during TCP option parsing in nf_osf_match_one() but not restored when returning early after a match. With NF_OSF_LOGLEVEL_ALL enabled, subsequent fingerprint checks read from the wrong buffer position, causing garbage data to be read.
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
>= 4.19.26, < 4.20>= 4.20.13, < 5.0>= 5.0.1, < 5.10.258>= 5.11, < 5.15.209>= 5.16, < 6.1.175>= 6.2, < 6.6.141>= 6.7, < 6.12.91>= 6.13, < 6.18.33>= 6.19, < 7.0.10= 5.0CVSS 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
- High
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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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Identify kernel versionRun 'uname -r' to get the running kernel version. Compare against the version where the nf_osf_match_one() fix was applied (check kernel changelogs for nfnetlink osf ctx->optp pointer restore fix)Affected if Kernel version is older than the fixed version and the osf module is in use
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Verify nfnetlink_osf module statusRun 'lsmod | grep nfnetlink_osf' or 'modinfo nfnetlink_osf' to check if the OS fingerprint netfilter module is loaded or availableAffected if The nfnetlink_osf module is loaded in memory
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Check for active netfilter osf rulesRun 'iptables -L -n -v' or 'nft list ruleset' and search for rules using the 'osf' match target (e.g., '-m osf', '--osf')Affected if Any iptables or nftables rules with osf matching are active
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Inspect netfilter osf configurationCheck '/proc/net/netfilter/nfnetlink_osf' if it exists, or use 'cat /sys/module/nfnetlink_osf/parameters/*' to view module parametersAffected if OS fingerprinting is configured or the osf sysfs/filesystem interface is present and active
The environment is affected if the kernel version is vulnerable, the nfnetlink_osf module is loaded, and netfilter rules using OS fingerprint matching (osf) are actively in use, enabling the out-of-bounds read condition in nf_osf_match_one().
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 · scoped4.205.05.10.258
Apply the upstream kernel patch that makes nf_osf_match_one() stateless by passing context as constant and using a local optp pointer for traversal. Until patched, consider disabling NF_OSF_LOGLEVEL_ALL or restricting netfilter OS fingerprint access to trusted users.
Linux Kernel >= 5.15.209 (LTS) or >= 5.10.258, depending on current branch
- 1. Identify current Linux kernel version using `uname -r`
- 2. Determine which version range the current kernel falls into (4.19.x, 4.20.x-5.0.x, 5.0.1-5.10.x, or 5.11-5.15.x)
- 3. For 4.19.x systems: upgrade to kernel >= 5.0 (ideally >= 5.15.209 for long-term support)
- 4. For 4.20.x-5.0.x systems: upgrade to kernel >= 5.10.258 (ideally >= 5.15.209)
- 5. For 5.0.1-5.10.x systems: upgrade to kernel >= 5.10.258
- 6. For 5.11-5.15.x systems: upgrade to kernel >= 5.15.209
- 7. After kernel upgrade, reboot the system to load the fixed kernel
- 8. Verify the fix is applied by checking the nfnetlink_osf module or kernel version
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Linux Kernel
Scoped from the published advisory
- Consultation2.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA3.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,096.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-52999 — 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-2026-52999 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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