# CVE-2026-98540: fprobe: Terminate the fgraph_data list when the reservation is not filled


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-98540, GHSA-9jj3-9f6g-g6xw, UBUNTU-CVE-2026-98540

## What is CVE-2026-98540?

CVE-2026-98540 is a vulnerability in Linux, published on 18 Oct 2026. 

### Official description

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

fprobe: Terminate the fgraph_data list when the reservation is not filled

fprobe_fgraph_entry() reserves shadow stack space for every fprobe with
an exit handler, but only fills it for those whose entry handler returns
0. fgraph_reserve_data() does not clear the area, so fprobe_return()
parses the unused tail as headers left over from an earlier call, and an
exit handler can run twice or despite its entry handler asking to skip
it.

Write a zero word after the last entry to terminate the walk. A zeroed
slot does not decode to a NULL fprobe on the arches that encode the
header into one unsigned long, since arch_decode_fprobe_header_fp() ORs
in FPROBE_HEADER_MSB_PATTERN, so make read_fprobe_header() return NULL
for a zeroed slot.

## Which versions are affected by CVE-2026-98540?


## How do I fix CVE-2026-98540?

Upgrade to a fixed version.

## Is CVE-2026-98540 being exploited?

There is no known exploitation of CVE-2026-98540 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98540 and fix it if it is affected.

What it is: CVE-2026-98540 is a vulnerability in Linux, published on 18 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-98540 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-2026-98540/ (Markdown: https://insights.sbomify.com/CVE-2026-98540/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98540
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98540
- OSV: https://osv.dev/vulnerability/CVE-2026-98540

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98540/
Summaries are generated and may contain mistakes; the official description above is the record.