# CVE-2026-68174: tracing: Fix union collision of module and refcnt for dynamic events

> A local attacker with low privileges can cause a kernel crash by triggering a null pointer dereference in the Linux kernel tracing subsystem via dynamic 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:** 10 Aug 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-68174, DEBIAN-CVE-2026-68174, GHSA-c2f7-rhw7-9m5r, UBUNTU-CVE-2026-68174

## What is CVE-2026-68174?

CVE-2026-68174 is a vulnerability in Linux, published on 10 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 union collision of module and refcnt for dynamic events

In 'struct trace_event_call', the 'module' pointer and the 'refcnt'
atomic variable share the same memory space in a union. For dynamic
events, the union member is 'refcnt', which acts as an active
reference counter.

When a dynamic event (such as kprobe, uprobe, fprobe, eprobe, or
wprobe) has a non-zero reference count (e.g. due to active event
triggers or perf attachments), its 'call->module' evaluates to a
small non-zero integer instead of NULL.

When filtering or setting events for a specific module (e.g., writing
':mod:<module>' to 'set_event'), the code in
'__ftrace_set_clr_event_nolock()' and 'update_event_fields()' reads
'call->module' directly without checking whether the event is dynamic.
This causes the kernel to treat the small integer (refcnt) as a
'struct module' pointer, leading to a NULL/invalid pointer dereference
(Oops) when dereferencing the module name.

Fix this by ensuring that the 'TRACE_EVENT_FL_DYNAMIC' flag is checked
before treating 'call->module' as a valid pointer in these code paths.

## Which versions are affected by CVE-2026-68174?


## How do I fix CVE-2026-68174?

Apply the vendor's patch.

## Is CVE-2026-68174 being exploited?

There is no known exploitation of CVE-2026-68174 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-68174 and fix it if it is affected.

What it is: CVE-2026-68174 is a vulnerability in Linux, published on 10 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-2026-68174 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-2026-68174/ (Markdown: https://insights.sbomify.com/CVE-2026-68174/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-68174
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-68174
- OSV: https://osv.dev/vulnerability/CVE-2026-68174

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-68174/
Summaries are generated and may contain mistakes; the official description above is the record.