# OSV-2021-777: Heap-use-after-free in xmlAddNextSibling

> A heap-use-after-free vulnerability in the XML parsing library allows attackers to cause denial of service or potentially execute code via crafted XML input.

- **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:** 20 May 2021

## What is OSV-2021-777?

OSV-2021-777 is an use after free vulnerability in libxml2, published on 20 May 2021. 

### Official description

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=34461

```
Crash type: Heap-use-after-free READ 4
Crash state:
xmlAddNextSibling
xmlXIncludeCopyRange
xmlXIncludeCopyXPointer
```

## Which versions are affected by OSV-2021-777?

1 open source package ship an affected version, including libxml2.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `libxml2` | OSS-Fuzz | All versions | None |

## How do I fix OSV-2021-777?

No fix has been published for OSV-2021-777 yet. Limit exposure of the affected software until one is available.

## Is OSV-2021-777 being exploited?

There is no known exploitation of OSV-2021-777 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for OSV-2021-777 and fix it if it is affected.

What it is: OSV-2021-777 is an use after free vulnerability in libxml2, published on 20 May 2021. 
Exploitation: There is no known exploitation of OSV-2021-777 in the wild and no public exploit code.

Affected packages and fixed versions:
- libxml2 (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-2021-777/ (Markdown: https://insights.sbomify.com/OSV-2021-777/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/OSV-2021-777

---
From sbomify Insights: https://insights.sbomify.com/OSV-2021-777/
Summaries are generated and may contain mistakes; the official description above is the record.