RUSTSEC-2023-0075: Unaligned write of u64 on 32-bit and 16-bit platforms

What to do

1. See which version you have: cargo tree -i unsafe-libyaml (it also shows which of your dependencies pulls it in).
2. Update within your version requirement: cargo update -p unsafe-libyaml. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for example unsafe-libyaml = "0.2.10") 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

Affected versions allocate memory using the alignment of usize and write data to it of type u64, without using core::ptr::write_unaligned. In platforms with sub-64bit alignment for usize (including wasm32 and x86) these writes are insufficiently aligned some of the time.

If using an ordinary optimized standard library, the bug exhibits Undefined Behavior so may or may not behave in any sensible way, depending on optimization settings and hardware and other things. If using a Rust standard library built with debug assertions enabled, the bug manifests deterministically in a crash (non-unwinding panic) saying _"ptr::write requires that the pointer argument is aligned and non-null"_.

No 64-bit platform is impacted by the bug.

The flaw was corrected by allocating with adequately high alignment on all platforms.

References

• Package: crates.io/crates/unsafe-libyaml
• Advisory: rustsec.org/advisories/RUSTSEC-2023-0075.html
• Report: github.com/dtolnay/unsafe-libyaml/issues/21

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

Other advisories for unsafe-libyaml

• UnmaintainedRUSTSEC-2024-0449 · 2024-03-25unsafe-libyaml is unmaintained

Full security history of unsafe-libyaml