# RUSTSEC-2026-0256: Several methods in `circular-buffer` drop elements before updating the buffer's start/end metadata.

> A panic during element drop in circular-buffer causes use-after-free or double-free, potentially leading to code execution or crashes.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Not stated
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Aug 2026

## What is RUSTSEC-2026-0256?

RUSTSEC-2026-0256 is an use after free vulnerability in circular-buffer, published on 11 Aug 2026. 

### Official description

Several methods in `circular-buffer` drop elements before updating the buffer's start/end metadata. If an element's `Drop` panics during the drop, the metadata update is skipped, so the buffer still treats the already-dropped elements as live. When the buffer is later dropped (or used after the panic is caught), those elements are visited again — a use-after-free / double-free reachable from safe Rust.

## 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.

## Fix

Fixed in `circular-buffer` 2.0.1 by adjusting the buffer's start/end metadata before the elements are dropped.

## Which versions are affected by RUSTSEC-2026-0256?

1 open source package ship an affected version, including circular-buffer.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `circular-buffer` | crates.io | From 0.0.0-0 | 2.0.1 |

## How do I fix RUSTSEC-2026-0256?

Upgrade circular-buffer to 2.0.1 or later.

## Is RUSTSEC-2026-0256 being exploited?

There is no known exploitation of RUSTSEC-2026-0256 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for RUSTSEC-2026-0256 and fix it if it is affected.

What it is: RUSTSEC-2026-0256 is an use after free vulnerability in circular-buffer, published on 11 Aug 2026. 
Exploitation: There is no known exploitation of RUSTSEC-2026-0256 in the wild and no public exploit code.

Affected packages and fixed versions:
- circular-buffer (crates.io): affected from 0.0.0-0; fixed in 2.0.1

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-2026-0256/ (Markdown: https://insights.sbomify.com/RUSTSEC-2026-0256/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/RUSTSEC-2026-0256

---
From sbomify Insights: https://insights.sbomify.com/RUSTSEC-2026-0256/
Summaries are generated and may contain mistakes; the official description above is the record.