# CVE-2026-74636: tracing: Fix race between update_event_fields and, event_define_fields

> A race condition in the Linux kernel tracing subsystem allows local attackers to cause a system crash by loading modules concurrently.

- **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:** 22 Aug 2026
- **Updated:** 22 Aug 2026
- **Also known as:** AZL-97325, BELL-CVE-2026-74636, DEBIAN-CVE-2026-74636, GHSA-jcq2-873m-mp53, UBUNTU-CVE-2026-74636

## What is CVE-2026-74636?

CVE-2026-74636 is a vulnerability in Linux, published on 22 Aug 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:

tracing: Fix race between update_event_fields and, event_define_fields

The following sequence may leads race between event_define_fields()
and update_event_fields():

 CPU0 (loads module A)                      CPU1 (loads module B)
 ===============================            ===============================
 load_module(A)                             load_module(B)
   notifier_call_chain                        notifier_call_chain
     trace_module_notify                        trace_module_notify
       mutex_lock(&event_mutex)                   trace_event_update_all()
         trace_module_add_events(A)                 down_write(&trace_event_sem)
            __register_event(call_A)
              __add_event_to_tracers(call_A)
                event_define_fields(call_A)
                  for each f:                         list_for_each_entry(field,
                    list_add(&f->link,                                    &class->fields, link)
                             &class->fields)            field = class->fields->next;

Where access to the class->fields is not protected by the event_mutex in
trace_event_update_all().

This produces the following panic:
   Unable to handle kernel access ... at virtual address 0000000000000018
   pc : update_event_fields+0xf8/0x368
   Call trace:
    update_event_fields+0xf8/0x368
    trace_event_update_all+0x7c/0x2b4
    trace_module_notify+0x4c/0x1dc
    notifier_call_chain+0x84/0x168
    blocking_notifier_call_chain_robust+0x64/0xd4
    load_module+0x10c8/0x123c
    __arm64_sys_finit_module+0x230/0x31c

Fix by taking event_mutex in trace_event_update_all() before
trace_event_sem.

## Which versions are affected by CVE-2026-74636?


## How do I fix CVE-2026-74636?

Apply the vendor's patch.

## Is CVE-2026-74636 being exploited?

There is no known exploitation of CVE-2026-74636 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74636 and fix it if it is affected.

What it is: CVE-2026-74636 is a vulnerability in Linux, published on 22 Aug 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-2026-74636 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-2026-74636/ (Markdown: https://insights.sbomify.com/CVE-2026-74636/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74636
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74636
- OSV: https://osv.dev/vulnerability/CVE-2026-74636

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74636/
Summaries are generated and may contain mistakes; the official description above is the record.