# CVE-2026-97526: s390/pai: Support CPU hotplug for PMU PAI

> A local attacker can cause a kernel panic via null pointer dereference in the s390 PAI PMU driver during CPU hotplug events.

- **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:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-97526, DEBIAN-CVE-2026-97526, GHSA-4mg4-96g4-2j54, UBUNTU-CVE-2026-97526

## What is CVE-2026-97526?

CVE-2026-97526 is a 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:

s390/pai: Support CPU hotplug for PMU PAI

The command 'perf stat -e pai_crypto/CRYPTO_ALL/ -- <command>'
crashes the kernel when CPUs are hotplug added during that run.

Root cause is the missing allocation of per-CPU data structures
for that new CPU. The allocation is dynamic and the first
event that has task context creates such a structure for
each online CPU. This is not sufficient. CPUs may be offline
during event creation and can be set online during the
perf run time. For example commands

 # echo 0 > /sys/devices/system/cpu/cpu1/online
 # perf stat -e cycles -i -- stress-ng -t10s --matrix X
 # sleep 1
 # echo 1 > /sys/devices/system/cpu/cpu1/online

Currently without a CPU hotplug handler, that new CPU has no
per-CPU data infrastructure. The scheduler runs PMU call back
function pai_add() to install the PMU support for that CPU before
the task is being scheduled on that new CPU.
In pai_add() instructions

    mp = this_cpu_ptr(pai_root[idx].mapptr);
    cpump = mp->mapptr;

return a NULL pointer and the result is a kernel panic as variable
cpump is used inside that function.

Add CPU hotplug support for CPU add and delete and create
the necessary per-CPU data infrastructure during CPU hotplug
add processing. Same for CPU hotplug remove.
This is done when the CPU is offline to ensure the data structures
are available when CPU is made online and tasks are scheduled on it.

[hca@linux.ibm.com: fixup error path in pai_init()]

## Which versions are affected by CVE-2026-97526?


## How do I fix CVE-2026-97526?

Apply the vendor's patch.

## Is CVE-2026-97526 being exploited?

There is no known exploitation of CVE-2026-97526 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-97526 and fix it if it is affected.

What it is: CVE-2026-97526 is a 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-2026-97526 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-2026-97526/ (Markdown: https://insights.sbomify.com/CVE-2026-97526/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-97526
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-97526
- OSV: https://osv.dev/vulnerability/CVE-2026-97526

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-97526/
Summaries are generated and may contain mistakes; the official description above is the record.