RUSTSEC-2026-0256: Panic-safety unsoundness in `truncate_back`, `truncate_front`, `clear`, and `extend_from_slice` (use-after-free / double-free)

What to do

1. See which version you have: cargo tree -i circular-buffer (it also shows which of your dependencies pulls it in).
2. Update within your version requirement: cargo update -p circular-buffer. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for example circular-buffer = "2.0.1") or update the dependency that pulls it in.
3. Check again with cargo audit, or paste your Cargo.lock into our Cargo.toml checker.

Details from the advisory

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.

References

• Package: crates.io/crates/circular-buffer
• Advisory: rustsec.org/advisories/RUSTSEC-2026-0256.html
• Web: github.com/andreacorbellini/rust-circular-buffer/blob/master/CHANGELOG.md

From the RustSec Advisory Database (CC0-1.0) via the OSV export, downloaded Oct 24, 2026. Severity score computed from the published CVSS vector.