# RUSTSEC-2026-0255: Panic-safety unsoundness in `Chunk`, `RingBuffer`, and `InlineArray` (use-after-free / double-free)

> A use-after-free and double-free vulnerability in the sized-chunks Rust library allows attackers to cause memory corruption or crashes via panicking Drop implementations.

- **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:** 11 Aug 2026

## What is RUSTSEC-2026-0255?

RUSTSEC-2026-0255 is an use after free vulnerability in sized-chunks, published on 11 Aug 2026. 

### Official description

Several methods in `sized-chunks` drop elements before updating the length/boundary metadata. If an element's `Drop` panics during the drop, the metadata update is skipped, so the container still treats the already-dropped elements as live. When the container's own `Drop` runs, those elements are visited again — a use-after-free / double-free reachable from safe Rust.

The `RingBuffer` methods require the `ringbuffer` feature. This is distinct from RUSTSEC-2020-0041 (`Chunk::clone` / `insert_from`, fixed in 0.6.3); the methods here are still affected in 0.7.0. The repository is archived with issues/PRs disabled and no fix available.

## Impact

- **CWE-415 (Double Free):** the same allocation is freed twice.
- **CWE-416 (Use-After-Free):** a freed allocation is accessed during a repeated `Drop`.

Reachable entirely from safe Rust via `catch_unwind` with element types whose `Drop` can panic.

## Which versions are affected by RUSTSEC-2026-0255?

1 open source package ship an affected version, including sized-chunks.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `sized-chunks` | crates.io | From 0.0.0-0 | None |

## How do I fix RUSTSEC-2026-0255?

No fix has been published for RUSTSEC-2026-0255 yet. Limit exposure of the affected software until one is available.

## Is RUSTSEC-2026-0255 being exploited?

There is no known exploitation of RUSTSEC-2026-0255 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for RUSTSEC-2026-0255 and fix it if it is affected.

What it is: RUSTSEC-2026-0255 is an use after free vulnerability in sized-chunks, published on 11 Aug 2026. 
Exploitation: There is no known exploitation of RUSTSEC-2026-0255 in the wild and no public exploit code.

Affected packages and fixed versions:
- sized-chunks (crates.io): affected from 0.0.0-0; 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/RUSTSEC-2026-0255/ (Markdown: https://insights.sbomify.com/RUSTSEC-2026-0255/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/RUSTSEC-2026-0255

---
From sbomify Insights: https://insights.sbomify.com/RUSTSEC-2026-0255/
Summaries are generated and may contain mistakes; the official description above is the record.