CVE-2026-52999: Linux kernel · netfilter: nfnetlink_osf: fix out-of-bounds read on option matching
Affects Linux kernelSource GCVE Database
Not known to be exploited · CVSS 9.1 Critical · fixed in 5.4.0-1162.173~18.04.1 : patch Linux kernel as a priority.
Data as of 26 Oct 2026, 14:05 UTC
- EPSS
- 0.5% chance of exploitation in 30 days – higher than 47% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 5.4.0-1162.173~18.04.1, 5.4.0-1167.173~18.04.1, 5.4.0-1165.174~18.04.1 +101
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:HExploitation evidence
Disclosed: evidence found.
CVE published 24 Jun 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Upgrade to a fixed release listed under Affected software.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 26.04 LTSlinuxpkg:deb/ubuntu/linux?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-awspkg:deb/ubuntu/linux-aws?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-azurepkg:deb/ubuntu/linux-azure?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-azure-fdepkg:deb/ubuntu/linux-azure-fde?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-gcppkg:deb/ubuntu/linux-gcp?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-gkepkg:deb/ubuntu/linux-gke?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
Description
In 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.
References
- ubuntu.com/security/CVE-2026-52999 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-52999 (opens in a new tab)
- git.kernel.org/linus/f5ca450087c3baf3651055e7a6de92600f827af3 (opens in a new tab)
- ubuntu.com/security/notices/USN-8566-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8568-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8569-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8567-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8574-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8575-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8576-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8593-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8574-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-8595-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8596-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8575-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-8576-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-8603-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8595-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-8606-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8607-1 (opens in a new tab)
- nvd.nist.gov/vuln/detail/CVE-2026-52999 (opens in a new tab)
- cert-portal.siemens.com/productcert/html/ssa-019113.html (opens in a new tab)
- git.kernel.org/stable/c/0145548346c4a30981a870a8ca00eac46ba27e85 (opens in a new tab)
- git.kernel.org/stable/c/1c136f2c44a5913646bac85303612fd0825197a0 (opens in a new tab)
- git.kernel.org/stable/c/1e19a07291bb8682c14c39a64725a3ae54ab8ccc (opens in a new tab)
- git.kernel.org/stable/c/21883587593d7c8bb519a79460a0b5bc5ffbdabd (opens in a new tab)
- git.kernel.org/stable/c/32e50f92c7cf3f4eba29622179a5fcdc2aebab41 (opens in a new tab)
- git.kernel.org/stable/c/70a3f31d25cf2ec9d4ddfa408120171ead955623 (opens in a new tab)
- git.kernel.org/stable/c/edb78a142d2e5948e63647c0646aa7e7886935f0 (opens in a new tab)
- git.kernel.org/stable/c/f5ca450087c3baf3651055e7a6de92600f827af3 (opens in a new tab)