# Panic-safety unsoundness in \`truncate_back\`, \`truncate_front\`, \`clear\`, and \`extend_from_slice\` (use-after-free / double-free)

Advisory record · `RUSTSEC-2026-0256`

- **Identifiers:** `RUSTSEC-2026-0256`
- **State:** Confirmed
- **Severity:** No CVSS score
- **Critical:** No
- **Published:** 11 Aug 2026
- **Updated:** 12 Aug 2026
- **Reviewed by a person:** No

Published by OSV at 11 Aug 2026, 12:00 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `circular-buffer` (crates.io): affected `>=0.0.0-0, <2.0.1`; fixed in `2.0.1`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> The circular-buffer crate before 2.0.1 is affected. Several methods (truncate_back, truncate_front, clear, extend_from_slice) drop elements before updating the buffer's metadata, so if an element's Drop panics, the buffer still treats already-dropped elements as live, leading to double-free or use-after-free. The source says this is reachable from safe Rust using catch_unwind with element types whose Drop can panic. Upgrade to circular-buffer 2.0.1, which fixes the ordering.

Written 8 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

No source has published a CVSS score for this record yet.

- **CISA KEV:** Not listed.
- **EPSS:** No score.

## Timeline

- 31 Oct 2026, 15:18 UTC: First seen by agentprime
- 31 Oct 2026, 15:18 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/RUSTSEC-2026-0256)

## Sources

- [OSV: RUSTSEC-2026-0256](https://osv.dev/vulnerability/RUSTSEC-2026-0256)
- <https://crates.io/crates/circular-buffer>
- <https://rustsec.org/advisories/RUSTSEC-2026-0256.html>
- <https://github.com/andreacorbellini/rust-circular-buffer/blob/master/CHANGELOG.md>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/RUSTSEC-2026-0256>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/RUSTSEC-2026-0256/>. Everything for agents: <https://agentprime.io/llms.txt>.