# RUSTSEC-2026-0290 - pqc_kyber: AVX2 backend skips Fujisaki-Okamoto implicit rejection, enabling chosen-ciphertext key recovery

Source: https://junglewise.ai/threats/rustsec-2026-0290-pqc-kyber-avx2-backend-skips-fujisaki-okamoto-5f69a5b0  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-16  
License: CC BY 4.0 with a link back

Severity: low · CVSS 3.1 · Published 2026-08-16

pqc_kyber: AVX2 backend skips Fujisaki-Okamoto implicit rejection, enabling chosen-ciphertext key recovery

Technologies: [pqc_kyber (crates.io)](https://junglewise.ai/threats/technologies/pqc-kyber). Vendors: [crates.io](https://junglewise.ai/threats/vendors/crates-io).

## Quick answers

**Is This vulnerability exploited in the wild?** No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

**How severe is This vulnerability?** Low severity, with a CVSS score of 3.1, published 16 August 2026.

**Which products and versions are affected?** pqc_kyber (crates.io) SEMVER:introduced=0.0.0-0.

**Is there a fix for This vulnerability?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**Am I affected?** Check whether you run pqc_kyber (crates.io) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Affected products

- pqc_kyber (crates.io) SEMVER:introduced=0.0.0-0

## Related threats

- [pqc_kyber Rust library unmaintained with unpatched flaw](https://junglewise.ai/threats/rustsec-2026-0289-pqc-kyber-is-unmaintained-e19367b2)
- [pqc_kyber KyberSlash: division timings depending on secrets](https://junglewise.ai/threats/pqc-kyber-kyberslash-division-timings-depending-on-secrets-93d94e36)
- [RUSTSEC-2023-0079 - KyberSlash: division timings depending on secrets](https://junglewise.ai/threats/rustsec-2023-0079-kyberslash-division-timings-depending-on-secrets-6aa36d51)