# CVE-2026-89742: rapidio: mport_cdev: fix use-after-free in dma_req_free()

> A use-after-free in the Linux kernel RapidIO mport driver allows local attackers to potentially execute code or escalate privileges via the character device interface.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-100718, BELL-CVE-2026-89742, DEBIAN-CVE-2026-89742, GHSA-hcj7-cp6w-gvx9, UBUNTU-CVE-2026-89742

## What is CVE-2026-89742?

CVE-2026-89742 is a high-severity use after free vulnerability in Linux, published on 11 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:

rapidio: mport_cdev: fix use-after-free in dma_req_free()

dma_req_free() acquires buf_mutex through req->map, drops the mapping
reference with kref_put(), and then dereferences req->map again to unlock
the mutex.

If kref_put() drops the last reference, mport_release_mapping() frees the
mapping, and the subsequent mutex_unlock() dereferences a freed object. 
This is a use-after-free.

Fix this by caching map and md before kref_put(), clearing req->map while
holding buf_mutex, and using the cached md for mutex unlocking.

The bug is reachable from userspace via the RapidIO mport character device
interface.

## Which versions are affected by CVE-2026-89742?


## How do I fix CVE-2026-89742?

Apply the vendor's patch.

## Is CVE-2026-89742 being exploited?

There is no known exploitation of CVE-2026-89742 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89742 and fix it if it is affected.

What it is: CVE-2026-89742 is a high-severity use after free vulnerability in Linux, published on 11 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-2026-89742 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-2026-89742/ (Markdown: https://insights.sbomify.com/CVE-2026-89742/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89742
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89742
- OSV: https://osv.dev/vulnerability/CVE-2026-89742

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89742/
Summaries are generated and may contain mistakes; the official description above is the record.