RUSTSEC-2026-0124: Potential Panic on Overlong Ciphertext Buffer

What to do

1. See which version you have: cargo tree -i libcrux-chacha20poly1305 (it also shows which of your dependencies pulls it in).
2. Update within your version requirement: cargo update -p libcrux-chacha20poly1305. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for example libcrux-chacha20poly1305 = "0.0.8") 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

An application that passes in a ciphertext buffer of length greater than ptxt.len() + TAG_LEN to libcrux_chacha20poly1305::encrypt or libcrux_chacha20poly1305::xchacha20_poly1305::encrypt would experience a panic.

Impact

An application where the length of the ciphertext buffer is under attacker control could be made to crash.

Mitigation

The fix makes it so that libcrux_chacha20poly1305::encrypt and libcrux_chacha20poly1305::xchacha20_poly1305::encrypt no longer panic in this case, but instead write out the ciphertext and tag into the first ptxt.len() + TAG_LEN bytes of the provided buffer.

References

• Package: crates.io/crates/libcrux-chacha20poly1305
• Advisory: rustsec.org/advisories/RUSTSEC-2026-0124.html
• Web: github.com/cryspen/libcrux/pull/1386

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