# OSV-2024-859: Heap-double-free in libssh2_default_free

> A heap double-free vulnerability in libssh2 allows remote attackers to cause a denial of service via crafted Diffie-Hellman key exchange packets.

- **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:** 16 Aug 2024

## What is OSV-2024-859?

OSV-2024-859 is an use after free vulnerability in libssh2, published on 16 Aug 2024. 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=69726

```
Crash type: Heap-double-free
Crash state:
libssh2_default_free
diffie_hellman_sha_algo
kex_method_diffie_hellman_group14_key_exchange
```

## Which versions are affected by OSV-2024-859?

1 open source package ship an affected version, including libssh2.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `libssh2` | OSS-Fuzz | All versions | None |

## How do I fix OSV-2024-859?

No fix has been published for OSV-2024-859 yet. Limit exposure of the affected software until one is available.

## Is OSV-2024-859 being exploited?

There is no known exploitation of OSV-2024-859 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for OSV-2024-859 and fix it if it is affected.

What it is: OSV-2024-859 is an use after free vulnerability in libssh2, published on 16 Aug 2024. 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-2024-859 in the wild and no public exploit code.

Affected packages and fixed versions:
- libssh2 (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-2024-859/ (Markdown: https://insights.sbomify.com/OSV-2024-859/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/OSV-2024-859

---
From sbomify Insights: https://insights.sbomify.com/OSV-2024-859/
Summaries are generated and may contain mistakes; the official description above is the record.