CVE-2026-52999

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 callers perspective, ensuring every fingerprint check starts at the correct option offset.

Weakness

The product reads data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

References

• https://git.kernel.org/stable/c/0145548346c4a30981a870a8ca00eac46ba27e85
• https://git.kernel.org/stable/c/1c136f2c44a5913646bac85303612fd0825197a0
• https://git.kernel.org/stable/c/1e19a07291bb8682c14c39a64725a3ae54ab8ccc
• https://git.kernel.org/stable/c/21883587593d7c8bb519a79460a0b5bc5ffbdabd
• https://git.kernel.org/stable/c/32e50f92c7cf3f4eba29622179a5fcdc2aebab41
• https://git.kernel.org/stable/c/70a3f31d25cf2ec9d4ddfa408120171ead955623
• https://git.kernel.org/stable/c/edb78a142d2e5948e63647c0646aa7e7886935f0
• https://git.kernel.org/stable/c/f5ca450087c3baf3651055e7a6de92600f827af3