CVE-2026-52999
CriticalCVSS 9.1Exploitation Probability (EPSS)
Low risk40th percentile — higher than 40% of all known CVEs
Summary
In the Linux kernel, a vulnerability in the netfilter nfnetlink_osf module causes an out-of-bounds read during TCP option matching. The issue occurs because the shared ctx->optp pointer is not restored after an early return in nf_osf_match_one(), leading to garbage data reads and incorrect logging when NF_OSF_LOGLEVEL_ALL is enabled.
Risk Assessment
The organization may experience incorrect logging of OS fingerprinting events, hindering security analysis and potentially masking real attacks.
Recommendation
Immediately update the Linux kernel to a version containing the fix, which replaces the shared ctx->optp pointer with a local optp variable to ensure correct processing of each fingerprint.
Original NVD description (English source)
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.