Linux Kernel BPF Scalar Forking Exploit (CVE-2026-31413)
CVE-2026-31413 Published on April 12, 2026
bpf: Fix unsound scalar forking in maybe_fork_scalars() for BPF_OR
In the Linux kernel, the following vulnerability has been resolved:
bpf: Fix unsound scalar forking in maybe_fork_scalars() for BPF_OR
maybe_fork_scalars() is called for both BPF_AND and BPF_OR when the
source operand is a constant. When dst has signed range [-1, 0], it
forks the verifier state: the pushed path gets dst = 0, the current
path gets dst = -1.
For BPF_AND this is correct: 0 & K == 0.
For BPF_OR this is wrong: 0 | K == K, not 0.
The pushed path therefore tracks dst as 0 when the runtime value is K,
producing an exploitable verifier/runtime divergence that allows
out-of-bounds map access.
Fix this by passing env->insn_idx (instead of env->insn_idx + 1) to
push_stack(), so the pushed path re-executes the ALU instruction with
dst = 0 and naturally computes the correct result for any opcode.
Products Associated with CVE-2026-31413
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Affected Versions
Linux:- Version dea9989a3f3961faede93752cd81eb5a9514d911 and below 342aa1ee995ef5bbf876096dc3a5e51218d76fa4 is affected.
- Version 4c122e8ae14950cf6b59d208fc5160f7c601e746 and below 58bd87d0e69204dbd739e4387a1edb0c4b1644e7 is affected.
- Version e52567173ba86dbffb990595fbe60e2e83899372 and below d13281ae7ea8902b21d99d10a2c8caf0bdec0455 is affected.
- Version bffacdb80b93b7b5e96b26fad64cc490a6c7d6c7 and below c845894ebd6fb43226b3118d6b017942550910c5 is affected.
- Version 7.0-rc1 is affected.
- Before 7.0-rc1 is unaffected.
- Version 6.12.80, <= 6.12.* is unaffected.
- Version 6.18.21, <= 6.18.* is unaffected.
- Version 6.19.11, <= 6.19.* is unaffected.
- Version 7.0-rc5, <= * is unaffected.