# OSV-2025-855: Use-of-uninitialized-value in AlphaReplace_SSE2

> A use-of-uninitialized-value bug in the WebP library's AlphaReplace_SSE2 function can cause a crash during image encoding.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Not stated
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 24 Oct 2025

## What is OSV-2025-855?

OSV-2025-855 is a vulnerability in libwebp, published on 24 Oct 2025. 

### Official description

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=454314139

```
Crash type: Use-of-uninitialized-value
Crash state:
AlphaReplace_SSE2
WebPReplaceTransparentPixels
WebPEncode
```

## Which versions are affected by OSV-2025-855?

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


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

## How do I fix OSV-2025-855?

No fix has been published for OSV-2025-855 yet. Limit exposure of the affected software until one is available.

## Is OSV-2025-855 being exploited?

There is no known exploitation of OSV-2025-855 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for OSV-2025-855 and fix it if it is affected.

What it is: OSV-2025-855 is a vulnerability in libwebp, published on 24 Oct 2025. 
Exploitation: There is no known exploitation of OSV-2025-855 in the wild and no public exploit code.

Affected packages and fixed versions:
- libwebp (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-2025-855/ (Markdown: https://insights.sbomify.com/OSV-2025-855/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/OSV-2025-855

---
From sbomify Insights: https://insights.sbomify.com/OSV-2025-855/
Summaries are generated and may contain mistakes; the official description above is the record.