Vulnerability HighRUSTSEC-2023-0079 · pqc_kyber
RUSTSEC-2023-0079: KyberSlash: division timings depending on secrets
Short answerA security vulnerability in the pqc_kyber crate: KyberSlash: division timings depending on secrets. High severity (CVSS 7.4). No fixed version: replace the crate or remove the affected code path.
| Crate | pqc_kyber |
|---|---|
| Type | Vulnerability (crypto-failure) |
| Affected versions | Every version. |
| Fixed in | none |
| Severity | High, CVSS 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N |
| Published | 2023-12-01 |
| Last changed | 2024-04-12 |
| Also known as | GHSA-x5j2-g63m-f8g4 |
What to do
- Find who pulls it in:
cargo tree -i pqc_kyber. - Avoid the affected API, or replace the crate.
Details from the advisory
Various Kyber software libraries in various environments leak secret information into timing, specifically because
- these libraries include a line of code that divides a secret numerator by a public denominator,
- the number of CPU cycles for division in various environments varies depending on the inputs to the division, and
- this variation appears within the range of numerators used in these libraries.
The KyberSlash pages track which Kyber libraries have this issue, and include a FAQ about the issue.
Author
The KyberSlash pages were written by Daniel J. Bernstein. The FAQ originally said "I", but some people seemed to have trouble finding this authorship statement, so the FAQ now says "Bernstein" instead.
URL
The permanent link for the KyberSlash pages is https://kyberslash.cr.yp.to.
Mitigation status in pqc_kyber crate
The issue has not been resolved in the upstream pqc_kyber crate.
A third-party fork that mitigates this attack vector has been published as safe_pqc_kyber.
Alternatives
The ml-kem crate is a maintained alternative pure Rust implementation of ML-KEM / Kyber.
References
- Package: crates.io/crates/pqc_kyber
- Advisory: rustsec.org/advisories/RUSTSEC-2023-0079.html
- Report: github.com/Argyle-Software/kyber/issues/108
- Web: kyberslash.cr.yp.to/faq.html
- Web: kyberslash.cr.yp.to/libraries.html
- Web: github.com/bwesterb/argyle-kyber/commit/b5c6ad13f4eece80e59c6ebeafd787ba1519f5f6
From the RustSec Advisory Database (CC0-1.0) via the OSV export, downloaded Oct 24, 2026. Severity score computed from the published CVSS vector.
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