# CVE-2026-41210: Moonlight Qt: Remote heap buffer overflow in Moonlight Qt H.264 SPS fixup path via crafted seq_parameter_set_id

> A malicious streaming host can cause a remote heap buffer overflow and crash the Moonlight Qt client by sending a crafted H.264 SPS NAL.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 12 Oct 2026
- **Updated:** 13 Oct 2026
- **Also known as:** GHSA-5rvh-v25g-vrgv

## What is CVE-2026-41210?

CVE-2026-41210 is a medium-severity memory corruption vulnerability in moonlight-stream moonlight-qt, published on 12 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Moonlight Qt is a GameStream client for Windows, macOS, Linux, and Steam Link. In version 6.1.0 and earlier, after a victim initiates a streaming session to a malicious host, the host can send a crafted H.264 SPS NAL when Moonlight selects a decoder path that does not advertise CAPABILITY_REFERENCE_FRAME_INVALIDATION_AVC. The SPS fixup path in app/streaming/video/ffmpeg.cpp parses the server-provided data with h264bitstream, where attacker-controlled seq_parameter_set_id is used to index the 32-entry sps_table without validation. A value of 32 or greater causes an out-of-bounds write and remote heap corruption in the Moonlight client. The demonstrated impact is a reliable client crash, while code execution is not established. This issue is fixed in version 6.2.0.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-41210?


## How do I fix CVE-2026-41210?

No fix has been published for CVE-2026-41210 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-41210 being exploited?

There is no known exploitation of CVE-2026-41210 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-41210 and fix it if it is affected.

What it is: CVE-2026-41210 is a medium-severity memory corruption vulnerability in moonlight-stream moonlight-qt, published on 12 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-41210 in the wild and no public exploit code.

Affected product: moonlight-stream moonlight-qt. 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-2026-41210/ (Markdown: https://insights.sbomify.com/CVE-2026-41210/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-41210
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-41210
- OSV: https://osv.dev/vulnerability/CVE-2026-41210

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-41210/
Summaries are generated and may contain mistakes; the official description above is the record.