# RUSTSEC-2026-0400: Use-after-free of a dictionary after a one-shot call on a context with an open stream


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 16 Oct 2026

## What is RUSTSEC-2026-0400?

RUSTSEC-2026-0400 is a vulnerability in zstd-safe, published on 16 Oct 2026. 

### Official description

The one-shot `DCtx` and `CCtx` methods assumed the C library resets the
context, but it leaves an open stream as it is. When a stream was left
unfinished on a context, a one-shot call such as `decompress_using_dict`
could leave the context pointing at the dictionary borrowed for that call,
and the next streaming call resumed the stream against it after it was
freed: decompressed output then contained freed heap memory. On the
compression side, the stream resumed against the one-shot call's buffers.

This requires an application to use one context for both streaming and
one-shot calls without a reset in between. The flaw was corrected by
resetting the session after one-shot calls whenever a stream may be open.

## Which versions are affected by RUSTSEC-2026-0400?

1 open source package ship an affected version, including zstd-safe.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `zstd-safe` | crates.io | From 3.0.1 | 8.2.0 |

## How do I fix RUSTSEC-2026-0400?

Upgrade zstd-safe to 8.2.0 or later.

## Is RUSTSEC-2026-0400 being exploited?

There is no known exploitation of RUSTSEC-2026-0400 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for RUSTSEC-2026-0400 and fix it if it is affected.

What it is: RUSTSEC-2026-0400 is a vulnerability in zstd-safe, published on 16 Oct 2026. 
Exploitation: There is no known exploitation of RUSTSEC-2026-0400 in the wild and no public exploit code.

Affected packages and fixed versions:
- zstd-safe (crates.io): affected from 3.0.1; fixed in 8.2.0

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/RUSTSEC-2026-0400/ (Markdown: https://insights.sbomify.com/RUSTSEC-2026-0400/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/RUSTSEC-2026-0400

---
From sbomify Insights: https://insights.sbomify.com/RUSTSEC-2026-0400/
Summaries are generated and may contain mistakes; the official description above is the record.