# CVE-2026-72111: bpf: Reset register bounds before narrowing retval range in check_mem_access()

> A flaw in the Linux kernel BPF verifier allows bypassing memory safety checks via stale register bounds, potentially enabling arbitrary code execution.

- **Severity:** High 8.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** BELL-CVE-2026-72111, DEBIAN-CVE-2026-72111, GHSA-vhcf-p8jc-x5f6, UBUNTU-CVE-2026-72111

## What is CVE-2026-72111?

CVE-2026-72111 is a high-severity vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

bpf: Reset register bounds before narrowing retval range in check_mem_access()

When the BPF verifier processes a context load of an LSM hook return
value, it calls __mark_reg_s32_range() to narrow the register to the
hook's valid range. However, __mark_reg_s32_range() intersects the new
range with the register's existing bounds using max_t()/min_t() rather
than replacing them.

If the destination register carries stale bounds from a prior instruction
(e.g. BPF_MOV64_IMM), the intersection can produce a range narrower than
reality. The verifier then believes it knows the register's exact value,
while at runtime the actual hook return value is loaded, creating a
verifier/runtime mismatch that can be used to bypass BPF memory safety
checks.

The else branch already calls mark_reg_unknown() to reset register state
before any narrowing. Apply the same reset in the is_retval path so
stale bounds are cleared before __mark_reg_s32_range() intersects.

## Which versions are affected by CVE-2026-72111?


## How do I fix CVE-2026-72111?

Apply the vendor's patch.

## Is CVE-2026-72111 being exploited?

There is no known exploitation of CVE-2026-72111 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72111 and fix it if it is affected.

What it is: CVE-2026-72111 is a high-severity vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-72111 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-72111/ (Markdown: https://insights.sbomify.com/CVE-2026-72111/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72111
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72111
- OSV: https://osv.dev/vulnerability/CVE-2026-72111

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72111/
Summaries are generated and may contain mistakes; the official description above is the record.