CVE-2026-23397: Linux kernel · nfnetlink_osf: validate individual option lengths in fingerprints
Affects Linux kernelSource GCVE Database
Not known to be exploited · CVSS 7.1 High · patch available : patch Linux kernel soon.
Data as of 26 Oct 2026, 14:05 UTC
- EPSS
- 0.1% chance of exploitation in 30 days – higher than 2% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:HExploitation evidence
Disclosed: evidence found.
CVE published 26 Mar 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
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 25.10linuxpkg:deb/ubuntu/linux@6.17.0-40.40?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-awspkg:deb/ubuntu/linux-aws@6.17.0-1019.19?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-azurepkg:deb/ubuntu/linux-azure@6.17.0-1020.20?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-azure-fdepkg:deb/ubuntu/linux-azure-fde@6.17.0-1017.17?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-gcppkg:deb/ubuntu/linux-gcp@6.17.0-1020.22?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-oraclepkg:deb/ubuntu/linux-oracle@6.17.0-1018.18?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
A patch is available and should be applied to affected Linux kernel versions. The vendor advisory from Ubuntu confirms that this issue has been fixed. Systems running affected versions should upgrade to the fixed kernel releases to mitigate the vulnerability. No additional mitigations are required as the fix rejects invalid fingerprints before packet matching.
Description
A vulnerability in the Linux kernel's nfnetlink_osf subsystem was resolved that involved improper validation of individual TCP option lengths in fingerprint matching. Specifically, zero-length options and MSS options with lengths less than 4 could cause null pointer dereferences and out-of-bounds reads, leading to kernel crashes. The issue was fixed by rejecting fingerprints with invalid option lengths during addition rather than during packet matching.
References
- ubuntu.com/security/CVE-2026-23397 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-23397 (opens in a new tab)
- git.kernel.org/linus/dbdfaae9609629a9569362e3b8f33d0a20fd783c (opens in a new tab)
- git.kernel.org/stable/c/224f4678812e1a7bc8341bcb666773a0aec5ea6f (opens in a new tab)
- git.kernel.org/stable/c/3932620c04c2938c93c0890c225960d3d34ba355 (opens in a new tab)
- git.kernel.org/stable/c/4c6aa008b913e808c4f4d3cde36cb1d9bb5967c6 (opens in a new tab)
- git.kernel.org/stable/c/aa0574182c46963c3cdb8cde46ec93aca21100d8 (opens in a new tab)
- git.kernel.org/stable/c/dbdfaae9609629a9569362e3b8f33d0a20fd783c (opens in a new tab)
- git.kernel.org/stable/c/ec8bf0571b142f29dc0b68ae2ac3952f7a464b38 (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-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-8597-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8595-2 (opens in a new tab)