Linux Kernel: nfnetlink_osf Option Length Validation leads to KASAN NULL Deref
CVE-2026-23397 Published on March 26, 2026
nfnetlink_osf: validate individual option lengths in fingerprints
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.
Products Associated with CVE-2026-23397
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Affected Versions
Linux:- Version 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384 and below aa0574182c46963c3cdb8cde46ec93aca21100d8 is affected.
- Version 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384 and below 224f4678812e1a7bc8341bcb666773a0aec5ea6f is affected.
- Version 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384 and below ec8bf0571b142f29dc0b68ae2ac3952f7a464b38 is affected.
- Version 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384 and below 3932620c04c2938c93c0890c225960d3d34ba355 is affected.
- Version 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384 and below 4c6aa008b913e808c4f4d3cde36cb1d9bb5967c6 is affected.
- Version 11eeef41d5f63c7d2f7fdfcc733eb7fb137cc384 and below dbdfaae9609629a9569362e3b8f33d0a20fd783c is affected.
- Version 2.6.31 is affected.
- Before 2.6.31 is unaffected.
- Version 6.1.167, <= 6.1.* is unaffected.
- Version 6.6.130, <= 6.6.* is unaffected.
- Version 6.12.78, <= 6.12.* is unaffected.
- Version 6.18.20, <= 6.18.* is unaffected.
- Version 6.19.10, <= 6.19.* is unaffected.
- Version 7.0-rc5, <= * is unaffected.