# CVE-2026-98047: bpf: Check ancestor frames for rbtree callbacks

> A local attacker can trigger a use-after-free in the Linux kernel BPF rbtree implementation via nested callbacks, potentially leading to privilege escalation or code execution.

- **Severity:** Not scored
- **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:** 25 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** BELL-CVE-2026-98047, DEBIAN-CVE-2026-98047, GHSA-4vcw-h5gp-c67p, UBUNTU-CVE-2026-98047

## What is CVE-2026-98047?

CVE-2026-98047 is an use after free vulnerability in Linux, published on 25 Sep 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: Check ancestor frames for rbtree callbacks

bpf_rbtree_add() invokes its comparator while the caller holds the root
lock. The native insertion code retains raw parent and link pointers across
the callback, so the verifier prohibits unlocking, consuming tree nodes,
or changing RCU state from that callback.

in_rbtree_lock_required_cb() only checks the innermost verifier frame.
Static subprogram calls are permitted while holding a spin lock, and such a
call pushes a frame without in_callback_fn set. Consequently, all callback
restrictions disappear in the nested frame. The subprogram can unlock the
tree, remove and drop the node being compared, then relock. Native insertion
resumes with the stale parent pointer and links freed memory into the tree.

Walk all active frames for the rbtree callback instead. Benign static
subprograms remain permitted, while callback restrictions follow execution
into nested frames.

## Which versions are affected by CVE-2026-98047?


## How do I fix CVE-2026-98047?

Apply the vendor's patch.

## Is CVE-2026-98047 being exploited?

There is no known exploitation of CVE-2026-98047 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98047 and fix it if it is affected.

What it is: CVE-2026-98047 is an use after free vulnerability in Linux, published on 25 Sep 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-2026-98047 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-2026-98047/ (Markdown: https://insights.sbomify.com/CVE-2026-98047/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98047
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98047
- OSV: https://osv.dev/vulnerability/CVE-2026-98047

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98047/
Summaries are generated and may contain mistakes; the official description above is the record.