# CVE-2026-99126: s390/ctcm: Prevent XID null dereference


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 28 Oct 2026
- **Updated:** 28 Oct 2026
- **Also known as:** AZL-111233, BELL-CVE-2026-99126, DEBIAN-CVE-2026-99126, GHSA-pcv7-392q-p29w, UBUNTU-CVE-2026-99126

## What is CVE-2026-99126?

CVE-2026-99126 is a vulnerability in Linux, published on 28 Oct 2026. 

### Official description

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

s390/ctcm: Prevent XID null dereference

The mpc_validate_xid() function sets grp->saved_xid2->xid2_flag2 to 0x40
to signal XID validation error. If peer XID is NULL or r/w channel
pairing mismatch happens, grp->saved_xid2 is never initialized. An
attempt to set the flag in such case leads to NULL dereference.

Fix this by using the always available priv->xid->xid2_flag2 instead of
grp->saved_xid2->xid2_flag2 for validation errors.

## Which versions are affected by CVE-2026-99126?


## How do I fix CVE-2026-99126?

Upgrade to a fixed version.

## Is CVE-2026-99126 being exploited?

There is no known exploitation of CVE-2026-99126 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99126 and fix it if it is affected.

What it is: CVE-2026-99126 is a vulnerability in Linux, published on 28 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99126 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-2026-99126/ (Markdown: https://insights.sbomify.com/CVE-2026-99126/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99126
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99126
- OSV: https://osv.dev/vulnerability/CVE-2026-99126

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99126/
Summaries are generated and may contain mistakes; the official description above is the record.