CVE-2026-43070

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

bpf: Reset register ID for BPF_END value tracking

When a register undergoes a BPF_END (byte swap) operation, its scalar value is mutated in-place. If this register previously shared a scalar ID with another register (e.g., after an r1 = r0 assignment), this tie must be broken.

Currently, the verifier misses resetting dst_reg->id to 0 for BPF_END. Consequently, if a conditional jump checks the swapped register, the verifier incorrectly propagates the learned bounds to the linked register, leading to false confidence in the linked registers value and potentially allowing out-of-bounds memory accesses.

Fix this by explicitly resetting dst_reg->id to 0 in the BPF_END case to break the scalar tie, similar to how BPF_NEG handles it via __mark_reg_known.

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/0d15c3611a2cc5d08993545d4032055ae10ae2c1
• https://git.kernel.org/stable/c/a17443af874229408ce6b78e2c8a2b5adeb4b7d8
• https://git.kernel.org/stable/c/a3125bc01884431d30d731461634c8295b6f0529