RUSTSEC-2026-0306 `hex_decode_unchecked` AVX2 path reads past `src`
A memory safety bug in the faster_hex library allows out-of-bounds reads on x86 systems with AVX2, potentially causing crashes or information disclosure.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Not stated
- Victim action needed
- Not needed
- Fix
- Available
What is RUSTSEC-2026-0306?
RUSTSEC-2026-0306 is a memory corruption vulnerability in faster-hex, published on 20 Sep 2026.
Official description
faster_hex::hex_decode_unchecked is a safe function. On x86 and x86_64, when AVX2 is enabled, hex_decode_avx2 keeps decoding while dst.len() >= 32 and then loads 32 bytes from src and 32 bytes from src[32..]. Nothing in that loop requires src to contain 64 bytes.
A safe caller can pass a short src and a dst of at least 32 bytes. The AVX2 load then reads outside src.
The function has had this shape since 0.3.0. 0.10.0 is the last release with the unbounded AVX2 read. The maintainer agreed to this advisory and shipped the backport in 0.10.1 (pull request 74): the AVX2 loop now requires src.len() >= 64 before those loads. 1.0.0 rewrites hex_decode_unchecked so the decoded length is min(src.len() / 2, dst.len()). Both are covered by >= 0.10.1. Other architectures take the scalar fallback and are outside this advisory.
Which versions are affected by RUSTSEC-2026-0306?
1 open source package ship an affected version, including faster-hex.
| Package | Affected | Fixed in |
|---|---|---|
faster-hex crates.io | From 0.3.0 | 0.10.1 |
How do I fix RUSTSEC-2026-0306?
Upgrade faster-hex to 0.10.1 or later.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is RUSTSEC-2026-0306 being exploited?
There is no known exploitation of RUSTSEC-2026-0306 in the wild and no public exploit code.