# CVE-2026-99163: tracing/histograms: Reject non-stacktrace fields for synthetic stacktrace fields


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 28 Oct 2026
- **Updated:** 28 Oct 2026
- **Also known as:** AZL-111305, BELL-CVE-2026-99163, DEBIAN-CVE-2026-99163, GHSA-8cf9-783r-h9xg, UBUNTU-CVE-2026-99163

## What is CVE-2026-99163?

CVE-2026-99163 is a vulnerability in Linux, published on 28 Oct 2026. 

### Official description

In the Linux kernel, the following vulnerability has been resolved:

tracing/histograms: Reject non-stacktrace fields for synthetic stacktrace fields

In check_synth_field(), when a synthetic event field is a stacktrace
(field->is_stack) and the histogram field is not a "long[" stacktrace
array, validation falls through to the generic size and signedness
comparison.

Because parse_synth_field() sets a stacktrace field's type to
"__data_loc unsigned long[]", its size is sizeof(u64) and
synth_field_signed() marks it as signed.  Consequently, any 8-byte
signed scalar histogram field passes the fallback check, and its scalar
value is subsequently dereferenced as a kernel stacktrace pointer in
get_field_size() and trace_stack().

Furthermore, checking strstr(hist_field->type, "long[") is insufficient
because tracepoint fields defined with __bitmask() or __rel_bitmask()
also have type "__data_loc unsigned long[]" or "__rel_loc unsigned
long[]", whilst create_hist_field() treats them as 4-byte scalar values
without HIST_FIELD_FL_STACKTRACE.

Propagate HIST_FIELD_FL_STACKTRACE to variable references and field
variables (whilst excluding variable aliases from per-element
stacktrace capture), and reject any mismatch between
HIST_FIELD_FL_STACKTRACE and field->is_stack in check_synth_field().

## Which versions are affected by CVE-2026-99163?


## How do I fix CVE-2026-99163?

Upgrade to a fixed version.

## Is CVE-2026-99163 being exploited?

There is no known exploitation of CVE-2026-99163 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99163 and fix it if it is affected.

What it is: CVE-2026-99163 is a vulnerability in Linux, published on 28 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99163 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-2026-99163/ (Markdown: https://insights.sbomify.com/CVE-2026-99163/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99163
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99163
- OSV: https://osv.dev/vulnerability/CVE-2026-99163

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99163/
Summaries are generated and may contain mistakes; the official description above is the record.