# CVE-2025-37878: perf/core: Fix WARN_ON(!ctx) in __free_event() for partial init

> A local attacker can trigger a kernel warning and potential crash in the Linux kernel's perf subsystem due to a null pointer dereference during event cleanup.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 9 May 2025
- **Updated:** 23 May 2026
- **Also known as:** AZL-70150, BELL-CVE-2025-37878, DEBIAN-CVE-2025-37878, GHSA-h3xh-892p-rrrq, ROOT-OS-DEBIAN-11-CVE-2025-37878, ROOT-OS-DEBIAN-12-CVE-2025-37878, ROOT-OS-UBUNTU-2204-CVE-2025-37878, ROOT-OS-UBUNTU-2404-CVE-2025-37878, UBUNTU-CVE-2025-37878

## What is CVE-2025-37878?

CVE-2025-37878 is a medium-severity vulnerability in Linux kernel, published on 9 May 2025. 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:

perf/core: Fix WARN_ON(!ctx) in __free_event() for partial init

Move the get_ctx(child_ctx) call and the child_event->ctx assignment to
occur immediately after the child event is allocated. Ensure that
child_event->ctx is non-NULL before any subsequent error path within
inherit_event calls free_event(), satisfying the assumptions of the
cleanup code.

Details:

There's no clear Fixes tag, because this bug is a side-effect of
multiple interacting commits over time (up to 15 years old), not
a single regression.

The code initially incremented refcount then assigned context
immediately after the child_event was created. Later, an early
validity check for child_event was added before the
refcount/assignment. Even later, a WARN_ON_ONCE() cleanup check was
added, assuming event->ctx is valid if the pmu_ctx is valid.
The problem is that the WARN_ON_ONCE() could trigger after the initial
check passed but before child_event->ctx was assigned, violating its
precondition. The solution is to assign child_event->ctx right after
its initial validation. This ensures the context exists for any
subsequent checks or cleanup routines, resolving the WARN_ON_ONCE().

To resolve it, defer the refcount update and child_event->ctx assignment
directly after child_event->pmu_ctx is set but before checking if the
parent event is orphaned. The cleanup routine depends on
event->pmu_ctx being non-NULL before it verifies event->ctx is
non-NULL. This also maintains the author's original intent of passing
in child_ctx to find_get_pmu_context before its refcount/assignment.

[ mingo: Expanded the changelog from another email by Gabriel Shahrouzi. ]

Weakness: CWE-617 (Reachable Assertion)

## Which versions are affected by CVE-2025-37878?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-37878?

Apply the vendor's patch.

## Is CVE-2025-37878 being exploited?

There is no known exploitation of CVE-2025-37878 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-37878 and fix it if it is affected.

What it is: CVE-2025-37878 is a medium-severity vulnerability in Linux kernel, published on 9 May 2025. 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-2025-37878 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2025-37878/ (Markdown: https://insights.sbomify.com/CVE-2025-37878/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-37878
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-37878
- OSV: https://osv.dev/vulnerability/CVE-2025-37878

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-37878/
Summaries are generated and may contain mistakes; the official description above is the record.