CVE-2026-31413

Public on 2026-04-12
Modified on 2026-04-16
Description
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.
Severity
Important severity
Important
See what this means
CVSS v3 Base Score
7.8
See breakdown

Affected Packages

Platform Package Release Date Advisory Status
Amazon Linux 2 - Core kernel Not Affected
Amazon Linux 2 - Kernel-5.10 Extra kernel Not Affected
Amazon Linux 2 - Kernel-5.15 Extra kernel Not Affected
Amazon Linux 2 - Kernel-5.4 Extra kernel Not Affected
Amazon Linux 2023 kernel Not Affected

CVSS Scores

Score Type Score Vector
Amazon Linux CVSSv3 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H