# RUSTSEC-2026-0344: Decompression bomb in `ruzstd`: a tiny input can exhaust memory (OOM)


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 11 Oct 2026

## What is RUSTSEC-2026-0344?

RUSTSEC-2026-0344 is a vulnerability in ruzstd, published on 11 Oct 2026. 

### Official description

A crafted `.zst` input under 128 KB can force `ruzstd` to allocate several gigabytes at once, crashing the process with an out-of-memory condition. Since `ruzstd` is a decoder for untrusted input, a single small file is enough to take down anything decoding it.

The compressed size of a block was capped at 128 KB, but a compressed block's **decompressed** size was never checked against `Block_Maximum_Size = min(Window_Size, 128 KiB)` (RFC 8878). In `execute_sequences` the output was built with no running bound and no flush between blocks, so one block could expand to gigabytes — bypassing both the configured window-size limit and the block-by-block streaming that would otherwise release memory. (A related `u32` counter overflow on such a block caused an additional panic.)

This is a denial of service only; memory access stays in bounds (no corruption, no RCE).

`ruzstd` is also built as a dependency of the Rust standard library via `rustc-dep-of-std`; in the toolchain it is used only to load zstd-compressed debug symbols, so the toolchain-side impact is limited.

**Fixed in 0.9.1** (commit `d3907c9`), which enforces the per-block output bound. Upgrade to `ruzstd >= 0.9.1`.

## Which versions are affected by RUSTSEC-2026-0344?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `ruzstd` | crates.io | From 0.0.0-0 | 0.9.1 |

## How do I fix RUSTSEC-2026-0344?

Upgrade ruzstd to 0.9.1 or later.

## Is RUSTSEC-2026-0344 being exploited?

There is no known exploitation of RUSTSEC-2026-0344 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for RUSTSEC-2026-0344 and fix it if it is affected.

What it is: RUSTSEC-2026-0344 is a vulnerability in ruzstd, published on 11 Oct 2026. 
Exploitation: There is no known exploitation of RUSTSEC-2026-0344 in the wild and no public exploit code.

Affected packages and fixed versions:
- ruzstd (crates.io): affected from 0.0.0-0; fixed in 0.9.1

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-2026-0344/ (Markdown: https://insights.sbomify.com/RUSTSEC-2026-0344/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/RUSTSEC-2026-0344

---
From sbomify Insights: https://insights.sbomify.com/RUSTSEC-2026-0344/
Summaries are generated and may contain mistakes; the official description above is the record.