Bug 2466789 (CVE-2026-43070)

Summary: CVE-2026-43070 kernel: bpf: Reset register ID for BPF_END value tracking
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's BPF (Berkeley Packet Filter) verifier. The verifier fails to correctly reset a register's ID after a BPF_END (byte swap) operation. This oversight can lead to the verifier incorrectly propagating learned memory bounds to other registers, creating false confidence in their values. Consequently, this could enable an attacker to perform out-of-bounds memory accesses, potentially leading to system instability or privilege escalation.
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Description OSIDB Bzimport 2026-05-05 17:02:51 UTC 
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 register's 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`.
Comment 1 Alexander B 2026-05-06 09:45:44 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050533-CVE-2026-43070-bcf9@gregkh/T