# CVE-2026-93275: perf/x86/intel/pt: Fix stop/start with no update

> A local attacker can trigger a kernel warning and potential instability by exploiting unbalanced AUX buffer operations in Intel PT tracing during group throttling.

- **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:** 24 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-103631, BELL-CVE-2026-93275, DEBIAN-CVE-2026-93275, GHSA-j5v2-xwxq-rp3v, UBUNTU-CVE-2026-93275

## What is CVE-2026-93275?

CVE-2026-93275 is a denial of service vulnerability in Linux, published on 24 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:

perf/x86/intel/pt: Fix stop/start with no update

If pt_event_stop() is called without PERF_EF_UPDATE flag, then
perf_aux_output_end() is not called.  A subsequent call to pt_event_start()
will call perf_aux_output_begin() again which violates the rule against
nesting and triggers a WARNING in perf_aux_output_begin().

Originally, pt_event_stop() was never called without PERF_EF_UPDATE,
because the only code paths to do so are from event overflow, and Intel PT
does not do that.

However the introduction of group throttling by commit 9734e25fbf5ae
("perf: Fix the throttle logic for a group") meant that an Intel PT event
could be throttled if it was part of a group.  Throttling calls PMU
 ->stop() / ->start() callbacks without flags.

An example is when AUX area sampling is used. The following commands
hit the issue:

  echo 10000 > /proc/sys/kernel/perf_event_max_sample_rate

  perf record -F32000 --aux-sample -e '{intel_pt//u,cycles:u}' \
  -- bash -c 'for i in `seq 1 100000` ; do true ; done'

Use PERF_HES_UPTODATE to track whether perf_aux_output_begin() and
perf_aux_output_end() are balanced.  A cleared PERF_HES_UPTODATE bit
indicates that an AUX output context is still open.

Amend pt_event_start() / pt_event_stop() accordingly so that begin/end
stay balanced:

 - In non-snapshot mode, stop() always closes the buffer (the buffer may
   have run out of space, and that accounting is done by the update), so
   a following start() opens a fresh one as before.

 - In snapshot/overwrite mode, stop() without PERF_EF_UPDATE leaves the
   buffer open so that pt_event_snapshot_aux() can still copy from it,
   and start() then only re-enables tracing instead of calling
   perf_aux_output_begin() again.

Note that pt_event_del() calls pt_event_stop() with PERF_EF_UPDATE flag set
(as is required by the documentation), so a final call to
perf_aux_output_end() is assured.

## Which versions are affected by CVE-2026-93275?


## How do I fix CVE-2026-93275?

Apply the vendor's patch.

## Is CVE-2026-93275 being exploited?

There is no known exploitation of CVE-2026-93275 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-93275 and fix it if it is affected.

What it is: CVE-2026-93275 is a denial of service vulnerability in Linux, published on 24 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-2026-93275 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-2026-93275/ (Markdown: https://insights.sbomify.com/CVE-2026-93275/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-93275
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-93275
- OSV: https://osv.dev/vulnerability/CVE-2026-93275

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-93275/
Summaries are generated and may contain mistakes; the official description above is the record.