# OSV-2020-671: Heap-use-after-free in WelsDec::SetUnRef

> A heap-use-after-free vulnerability in the OpenH264 decoder allows attackers to execute arbitrary code or cause denial of service via crafted media files.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 1 Jul 2020

## What is OSV-2020-671?

OSV-2020-671 is an use after free vulnerability in openh264, published on 1 Jul 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=18743

```
Crash type: Heap-use-after-free WRITE 1
Crash state:
WelsDec::SetUnRef
WelsDec::SlidingWindow
WelsDec::WelsMarkAsRef
```

## Which versions are affected by OSV-2020-671?

1 open source package ship an affected version, including openh264.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `openh264` | OSS-Fuzz | All versions | None |

## How do I fix OSV-2020-671?

No fix has been published for OSV-2020-671 yet. Limit exposure of the affected software until one is available.

## Is OSV-2020-671 being exploited?

There is no known exploitation of OSV-2020-671 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for OSV-2020-671 and fix it if it is affected.

What it is: OSV-2020-671 is an use after free vulnerability in openh264, published on 1 Jul 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of OSV-2020-671 in the wild and no public exploit code.

Affected packages and fixed versions:
- openh264 (OSS-Fuzz): affected all versions; no fix listed

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/OSV-2020-671/ (Markdown: https://insights.sbomify.com/OSV-2020-671/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/OSV-2020-671

---
From sbomify Insights: https://insights.sbomify.com/OSV-2020-671/
Summaries are generated and may contain mistakes; the official description above is the record.