VulnerabilityPublished 26 Mar 2026Updated 5 Nov 2026

CVE-2026-23397: Linux kernel · nfnetlink_osf: validate individual option lengths in fingerprints

Affects Linux kernelSource CVE Database V5

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Not known to be exploited · fixed in ec8bf0571b142f29dc0b68ae2ac3952f7a464b38 : update Linux kernel when convenient.

Data as of 5 Nov 2026, 22:04 UTC

Severity

Unrated

Rated by Threat Radar · No CVSS score from NVD or the CNA

Thin evidence

One scorer or none

Exploitation: No evidence of active exploitation and no public proof of concept
Automatable: Attackers cannot reliably automate steps 1–4 of the kill chain
Technical impact: Limited control over the software or limited information exposure

CISA SSVC assessment, 2026-11-05.

Patch

Available – fixed in ec8bf0571b142f29dc0b68ae2ac3952f7a464b38, e9cf17b91e733fec725ebcc0b3098bc5ccd505e0, dbdfaae9609629a9569362e3b8f33d0a20fd783c +5

Exploitation evidence

Disclosed: evidence found.
CVE published 26 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 5 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384, < ec8bf0571b142f29dc0b68ae2ac3952f7a464b38	Fixed in ec8bf0571b142f29dc0b68ae2ac3952f7a464b38
LinuxLinux	Affected ≥ 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384, < e9cf17b91e733fec725ebcc0b3098bc5ccd505e0	Fixed in e9cf17b91e733fec725ebcc0b3098bc5ccd505e0
LinuxLinux	Affected ≥ 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384, < dbdfaae9609629a9569362e3b8f33d0a20fd783c	Fixed in dbdfaae9609629a9569362e3b8f33d0a20fd783c
LinuxLinux	Affected ≥ 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384, < aa0574182c46963c3cdb8cde46ec93aca21100d8	Fixed in aa0574182c46963c3cdb8cde46ec93aca21100d8
LinuxLinux	Affected ≥ 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384, < 3932620c04c2938c93c0890c225960d3d34ba355	Fixed in 3932620c04c2938c93c0890c225960d3d34ba355
LinuxLinux	Affected ≥ 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384, < 224f4678812e1a7bc8341bcb666773a0aec5ea6f	Fixed in 224f4678812e1a7bc8341bcb666773a0aec5ea6f

Description

In the Linux kernel, the following vulnerability has been resolved: nfnetlink_osf: validate individual option lengths in fingerprints nfnl_osf_add_callback() validates opt_num bounds and string NUL-termination but does not check individual option length fields. A zero-length option causes nf_osf_match_one() to enter the option matching loop even when foptsize sums to zero, which matches packets with no TCP options where ctx->optp is NULL: Oops: general protection fault KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] RIP: 0010:nf_osf_match_one (net/netfilter/nfnetlink_osf.c:98) Call Trace: nf_osf_match (net/netfilter/nfnetlink_osf.c:227) xt_osf_match_packet (net/netfilter/xt_osf.c:32) ipt_do_table (net/ipv4/netfilter/ip_tables.c:293) nf_hook_slow (net/netfilter/core.c:623) ip_local_deliver (net/ipv4/ip_input.c:262) ip_rcv (net/ipv4/ip_input.c:573) Additionally, an MSS option (kind=2) with length < 4 causes out-of-bounds reads when nf_osf_match_one() unconditionally accesses optp[2] and optp[3] for MSS value extraction. While RFC 9293 section 3.2 specifies that the MSS option is always exactly 4 bytes (Kind=2, Length=4), the check uses "< 4" rather than "!= 4" because lengths greater than 4 do not cause memory safety issues -- the buffer is guaranteed to be at least foptsize bytes by the ctx->optsize == foptsize check. Reject fingerprints where any option has zero length, or where an MSS option has length less than 4, at add time rather than trusting these values in the packet matching hot path.

References

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