# CVE-2026-97938: reboot: fix cad_pid use-after-free race

> A use-after-free race condition in the Linux kernel's reboot subsystem allows local attackers to cause denial of service or potentially escalate privileges.

- **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:** AZL-104592, BELL-CVE-2026-97938, DEBIAN-CVE-2026-97938, GHSA-9x8r-8wjj-jgjv, UBUNTU-CVE-2026-97938

## What is CVE-2026-97938?

CVE-2026-97938 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:

reboot: fix cad_pid use-after-free race

cad_pid is a single kernel-wide struct pid pointer. proc_do_cad_pid()
reads it and passes it to pid_vnr() without protecting the lifetime of
the referenced struct pid. A concurrent writer can replace cad_pid and
drop the final reference to the old struct pid after the reader has
loaded the pointer but before pid_vnr() has finished dereferencing it,
causing a use-after-free.

kill_cad_pid() has the same lifetime race when it passes cad_pid to
kill_pid().

At the time this issue was reported, an unprivileged user could reach the
sysctl through user and PID namespaces because cad_pid was registered in
pid_table[]. Moving cad_pid back to the global reboot sysctl table
corrected that namespace and permission mismatch, but did not fix the
underlying lifetime race.

Fix this by treating cad_pid as an RCU-protected pointer at both read
sites and by waiting for a grace period before dropping the old reference
on the write side.

call_rcu(&old_pid->rcu, ...) cannot be used here because free_pid()
also queues pid->rcu; queueing the same rcu_head twice can corrupt the
RCU callback list.

Original KASAN crash stack:
  kernel/pid.c:545 pid_nr_ns()        # reads freed pid->level
  kernel/pid.c:556 pid_vnr()          # calls pid_nr_ns()
  kernel/pid.c:775 proc_do_cad_pid()  # calls pid_vnr(cad_pid)

## Which versions are affected by CVE-2026-97938?


## How do I fix CVE-2026-97938?

Apply the vendor's patch.

## Is CVE-2026-97938 being exploited?

There is no known exploitation of CVE-2026-97938 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-97938 and fix it if it is affected.

What it is: CVE-2026-97938 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-2026-97938 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-2026-97938/ (Markdown: https://insights.sbomify.com/CVE-2026-97938/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-97938
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-97938
- OSV: https://osv.dev/vulnerability/CVE-2026-97938

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-97938/
Summaries are generated and may contain mistakes; the official description above is the record.