# RUSTSEC-2026-0395: Use-after-free with `CParameter::StableInBuffer`


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

## What is RUSTSEC-2026-0395?

RUSTSEC-2026-0395 is a vulnerability in zstd-safe, published on 16 Oct 2026. 

### Official description

With `CParameter::StableInBuffer(true)` (`experimental` feature), the C
library keeps a pointer to the input of one streaming call and reads from it
in later calls, including `flush_stream` and `end_stream`, which take no
input. An `InBuffer` only borrows its slice for one call, so safe code could
free it in between, and freed memory was compressed into the frame. The C
library behaves this way since zstd 1.5.4, whether bundled or linked from the
system.

The flaw was corrected by refusing to enable the parameter.

## Which versions are affected by RUSTSEC-2026-0395?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `zstd-safe` | crates.io | From 4.1.0 | 8.2.0 |

## How do I fix RUSTSEC-2026-0395?

Upgrade zstd-safe to 8.2.0 or later.

## Is RUSTSEC-2026-0395 being exploited?

There is no known exploitation of RUSTSEC-2026-0395 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for RUSTSEC-2026-0395 and fix it if it is affected.

What it is: RUSTSEC-2026-0395 is a vulnerability in zstd-safe, published on 16 Oct 2026. 
Exploitation: There is no known exploitation of RUSTSEC-2026-0395 in the wild and no public exploit code.

Affected packages and fixed versions:
- zstd-safe (crates.io): affected from 4.1.0; 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-2026-0395/ (Markdown: https://insights.sbomify.com/RUSTSEC-2026-0395/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/RUSTSEC-2026-0395

---
From sbomify Insights: https://insights.sbomify.com/RUSTSEC-2026-0395/
Summaries are generated and may contain mistakes; the official description above is the record.