# CVE-2026-74391: tracing: Bound synthetic-field strings with seq_buf

> A buffer overflow in Linux kernel tracing allows local attackers to execute arbitrary code or escalate privileges via crafted synthetic field strings.

- **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:** 15 Aug 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-74391, DEBIAN-CVE-2026-74391, GHSA-853c-pg29-mfgr, UBUNTU-CVE-2026-74391

## What is CVE-2026-74391?

CVE-2026-74391 is a memory corruption vulnerability in Linux, published on 15 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: Bound synthetic-field strings with seq_buf

The synthetic field helpers build a prefixed synthetic variable name and
a generated hist command in fixed MAX_FILTER_STR_VAL buffers. The
current code appends those strings with raw strcat(), so long key lists,
field names, or saved filters can run past the end of the staging
buffers.

Build both strings with seq_buf and propagate -E2BIG if either the
synthetic variable name or the generated command exceeds
MAX_FILTER_STR_VAL. This keeps the existing tracing-side limit while
using the helper intended for bounded command construction.

[ sdr: Moved struct seq_buf *s for upside-down x-mas tree formatting ]

## Which versions are affected by CVE-2026-74391?


## How do I fix CVE-2026-74391?

Apply the vendor's patch.

## Is CVE-2026-74391 being exploited?

There is no known exploitation of CVE-2026-74391 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74391 and fix it if it is affected.

What it is: CVE-2026-74391 is a memory corruption vulnerability in Linux, published on 15 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-2026-74391 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-2026-74391/ (Markdown: https://insights.sbomify.com/CVE-2026-74391/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74391
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74391
- OSV: https://osv.dev/vulnerability/CVE-2026-74391

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74391/
Summaries are generated and may contain mistakes; the official description above is the record.