CVE-2026-52927

In the Linux kernel, the following vulnerability has been resolved:

netfilter: ebtables: fix OOB read in compat_mtw_from_user

Luxiao Xu says:

The function compat_mtw_from_user() converts ebtables extensions from 32-bit user structures to kernel native structures. However, it lacks proper validation of the user-supplied match_size/target_size.

When certain extensions are processed, the kernel-side translation logic may perform memory accesses based on the extensions expected size. If the user provides a size smaller than what the extension requires, it results in an out-of-bounds read as reported by KASAN.

This fix introduces a check to ensure match_size is at least as large as the extensions required compatsize. This covers matches, watchers, and targets, while maintaining compatibility with standard targets.

AFAIU this is relevant for matches that need to go though match->compat_from_user() call. Those that use plain memcpy with the user-provided size are ok because the caller checks that size vs the start of the next rule entry offset (which itself is checked vs. total size copied from userspace).

The ->compat_from_user() callbacks assume they can read compatsize bytes, so they need this extra check.

Based on an earlier patch from Luxiao Xu.

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/21af4c030567d2e6c89bb927bc18b51fba52a400
• https://git.kernel.org/stable/c/7ad0e463fc7eafae2141cc38054264636f8b3e94
• https://git.kernel.org/stable/c/a27cb7325a6c69970041c7f8541fafed5a1ea3ec
• https://git.kernel.org/stable/c/bf8e8eac7ede51dc318e06acef5a896dcbba7595
• https://git.kernel.org/stable/c/d7a8fb6f10d55a1c37b0bf8c20cca24dffd76e00
• https://git.kernel.org/stable/c/dad9ebf8107955bb54bd3f9cf22591b6ff37bac1
• https://git.kernel.org/stable/c/f438d1786d657d57790c5d138d6db3fc9fdac392
• https://git.kernel.org/stable/c/fcc4c043d137e7f1de4673dba1f3116e45377c67