# CVE-2026-68429: drm/dp_mst: Handle torn-down topology gracefully in drm_dp_mst_topology_queue_probe()

> A race condition in the Linux kernel DP MST driver causes compositor crashes when connecting or disconnecting monitors, requiring local physical access.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 12 Aug 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-68429, DEBIAN-CVE-2026-68429, GHSA-47qh-xgqx-2fv5, UBUNTU-CVE-2026-68429

## What is CVE-2026-68429?

CVE-2026-68429 is a vulnerability in Linux, published on 12 Aug 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

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

drm/dp_mst: Handle torn-down topology gracefully in drm_dp_mst_topology_queue_probe()

A hotplug or link-loss event can tear down the MST topology
(setting mgr->mst_state = false and mgr->mst_primary = NULL) concurrently
with a caller invoking drm_dp_mst_topology_queue_probe(). Since the check
is already performed under mgr->lock, the condition is not a programming
error but a valid race -- the topology was valid when the caller decided
to call this function, but was torn down before the lock was acquired.

Replace the drm_WARN_ON() with a graceful early return. This eliminates
spurious kernel warnings and the resulting compositor crashes observed
when connecting/disconnecting DP MST monitors, while keeping the correct
behavior of doing nothing when MST is not active. A drm_dbg_mst() trace
is added so the skipped probe remains observable under MST debug logging.

The existing WARN_ON(mgr->mst_primary) in drm_dp_mst_topology_mgr_set_mst()
already catches the case where the topology is initialized twice, so no
diagnostic coverage is lost.

## Which versions are affected by CVE-2026-68429?


## How do I fix CVE-2026-68429?

Apply the vendor's patch.

## Is CVE-2026-68429 being exploited?

There is no known exploitation of CVE-2026-68429 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-68429 and fix it if it is affected.

What it is: CVE-2026-68429 is a vulnerability in Linux, published on 12 Aug 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-68429 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-2026-68429/ (Markdown: https://insights.sbomify.com/CVE-2026-68429/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-68429
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-68429
- OSV: https://osv.dev/vulnerability/CVE-2026-68429

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-68429/
Summaries are generated and may contain mistakes; the official description above is the record.