# CVE-2026-98800: bpf: Wait for an RCU tasks grace period before freeing trampoline progs

> A use-after-free in the Linux kernel BPF trampoline allows local attackers with high privileges to execute arbitrary code or escalate privileges.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-108831, BELL-CVE-2026-98800, DEBIAN-CVE-2026-98800, GHSA-hw45-3jc9-w8mr, UBUNTU-CVE-2026-98800

## What is CVE-2026-98800?

CVE-2026-98800 is an use after free vulnerability in Linux, published on 18 Oct 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: Wait for an RCU tasks grace period before freeing trampoline progs

When a prog is detached from a trampoline, it is freed after an RCU
grace period, or an RCU tasks trace one if it is sleepable. This covers
the tasks that are running the prog, since the prog's enter helper takes
the matching read lock before the prog is called. On a preemptible
kernel, it doesn't cover a task that was preempted in the trampoline
just before the enter helper. That task holds no lock yet, and it calls
the prog after it was freed:

  BUG: KASAN: vmalloc-out-of-bounds in __bpf_prog_enter_recur+0x3a5/0x3f0
  Read of size 8 at addr ffffc90000055040 by task candidate/110
  CPU: 1 UID: 0 PID: 110 Comm: candidate Not tainted 7.3.0-rc2-00014-g15071f2a1263-dirty #2 PREEMPT(full)
  Call Trace:
   <TASK>
   __bpf_prog_enter_recur+0x3a5/0x3f0
   bpf_trampoline_6442509193+0x37/0xf1
   __x64_sys_futex+0x9/0x410
   do_syscall_64+0xb0/0x530
   ...

Wait for an RCU tasks grace period before the existing one when freeing
a prog that was linked to a trampoline. An RCU tasks grace period only
ends once the tasks that were preempted have run again, and
bpf_tramp_image_put() already relies on it to free the image. It doesn't
wait for tasks that sleep in the trampoline, the next commit takes care
of those.

Only progs that were linked to a trampoline can be called this way, so
bpf_trampoline_add_prog() marks them and other progs are still freed as
before.

## Which versions are affected by CVE-2026-98800?


## How do I fix CVE-2026-98800?

Apply the vendor's patch.

## Is CVE-2026-98800 being exploited?

There is no known exploitation of CVE-2026-98800 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98800 and fix it if it is affected.

What it is: CVE-2026-98800 is an use after free vulnerability in Linux, published on 18 Oct 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-2026-98800 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-2026-98800/ (Markdown: https://insights.sbomify.com/CVE-2026-98800/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98800
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98800
- OSV: https://osv.dev/vulnerability/CVE-2026-98800

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98800/
Summaries are generated and may contain mistakes; the official description above is the record.