# OSV-2021-871: Heap-use-after-free in jxl::ImageBlender::PrepareBlending

> A heap-use-after-free in the JPEG XL library allows attackers to execute arbitrary code or cause denial of service via crafted images.

- **Severity:** Not scored
- **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:** 18 Jun 2021

## What is OSV-2021-871?

OSV-2021-871 is an use after free vulnerability in libjxl, published on 18 Jun 2021. 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

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=35293

```
Crash type: Heap-use-after-free READ 8
Crash state:
jxl::ImageBlender::PrepareBlending
jxl::FinalizeFrameDecoding
jxl::FrameDecoder::Flush
```

## Which versions are affected by OSV-2021-871?

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


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

## How do I fix OSV-2021-871?

No fix has been published for OSV-2021-871 yet. Limit exposure of the affected software until one is available.

## Is OSV-2021-871 being exploited?

There is no known exploitation of OSV-2021-871 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for OSV-2021-871 and fix it if it is affected.

What it is: OSV-2021-871 is an use after free vulnerability in libjxl, published on 18 Jun 2021. 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 OSV-2021-871 in the wild and no public exploit code.

Affected packages and fixed versions:
- libjxl (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-2021-871/ (Markdown: https://insights.sbomify.com/OSV-2021-871/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/OSV-2021-871

---
From sbomify Insights: https://insights.sbomify.com/OSV-2021-871/
Summaries are generated and may contain mistakes; the official description above is the record.