# CVE-2026-72427: bpf: Fix effective prog array index with BPF_F_PREORDER

> A logic error in Linux kernel BPF program array indexing causes use-after-free, potentially allowing local attackers to execute code or escalate privileges.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/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-2026-72427, DEBIAN-CVE-2026-72427, GHSA-6pxh-c54r-cxc3, UBUNTU-CVE-2026-72427

## What is CVE-2026-72427?

CVE-2026-72427 is a high-severity use after free 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: Fix effective prog array index with BPF_F_PREORDER

replace_effective_prog() and purge_effective_progs() located the slot in
the effective array by walking the program hlist and counting entries
linearly. That count does not match the array layout: compute_effective_
progs() places BPF_F_PREORDER programs at the front (ancestor cgroup
first, attach order within a cgroup) and the rest after them (descendant
cgroup first). So when a preorder program is present, the linear hlist
position no longer equals the program's index in the effective array.

For replace_effective_prog() (bpf_link_update()) this overwrote the
wrong slot, corrupting the effective order. For purge_effective_progs(),
it could dummy out a slot belonging to a different program and leave the
detached program in the array while bpf_prog_put() drops its reference,
i.e. a use-after-free.

Fix both by replaying compute_effective_progs()'s placement (including
the per-cgroup preorder reversal) in a shared effective_prog_pos()
helper. Identify the entry by its struct bpf_prog_list pointer rather
than by (prog, link) value, so the lookup resolves to exactly the
attachment the syscall selected even when the same bpf_prog is attached
to several cgroups in the hierarchy.

## Which versions are affected by CVE-2026-72427?


## How do I fix CVE-2026-72427?

Apply the vendor's patch.

## Is CVE-2026-72427 being exploited?

There is no known exploitation of CVE-2026-72427 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72427 and fix it if it is affected.

What it is: CVE-2026-72427 is a high-severity use after free 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-2026-72427 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-2026-72427/ (Markdown: https://insights.sbomify.com/CVE-2026-72427/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72427
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72427
- OSV: https://osv.dev/vulnerability/CVE-2026-72427

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72427/
Summaries are generated and may contain mistakes; the official description above is the record.