CVE-2026-43025

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

netfilter: ctnetlink: ignore explicit helper on new expectations

Use the existing master conntrack helper, anything else is not really supported and it just makes validation more complicated, so just ignore what helper userspace suggests for this expectation.

This was uncovered when validating CTA_EXPECT_CLASS via different helper provided by userspace than the existing master conntrack helper:

BUG: KASAN: slab-out-of-bounds in nf_ct_expect_related_report+0x2479/0x27c0 Read of size 4 at addr ffff8880043fe408 by task poc/102 Call Trace: nf_ct_expect_related_report+0x2479/0x27c0 ctnetlink_create_expect+0x22b/0x3b0 ctnetlink_new_expect+0x4bd/0x5c0 nfnetlink_rcv_msg+0x67a/0x950 netlink_rcv_skb+0x120/0x350

Allowing to read kernel memory bytes off the expectation boundary.

CTA_EXPECT_HELP_NAME is still used to offer the helper name to userspace via netlink dump.

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/0f6c33697ccfac6499d0b7a4dbdec5d3a3a566cd
• https://git.kernel.org/stable/c/187b6ec5229ea93cb04c4f6d3b52efc80f513d0d
• https://git.kernel.org/stable/c/21a04c31db4057deec85fcd6cc63d720b38819c3
• https://git.kernel.org/stable/c/2ea0f35f235f70c133ad61fe05ba013753b978c6
• https://git.kernel.org/stable/c/917b61fa2042f11e2af4c428e43f08199586633a
• https://git.kernel.org/stable/c/e135f8e8212cbed12a03ab8dec77fa1247139897