Impact

When sampling randomness for a shared secret, the implementation of Kyber and FrodoKEM, did not check whether crypto/rand.Read() returns an error. In rare deployment cases (error thrown by the Read() function), this could lead to a predictable shared secret.

The tkn20 and blindrsa components did not check whether enough randomness was returned from the user provided randomness source. Typically the user provides crypto/rand.Reader, which in the vast majority of cases will always return the right number random bytes. In the cases where it does not, or the user provides a source that does not, the blinding for blindrsa is weak and integrity of the plaintext is not ensured in tkn20.

Patches

The fix was introduced in CIRCL v. 1.3.3

• https://github.com/cloudflare/circl/security/advisories/GHSA-2q89-485c-9j2x
• https://nvd.nist.gov/vuln/detail/CVE-2023-1732
• https://github.com/cloudflare/circl/commit/ff8d91225f8954b4970b6d6382d2e4c78f4a4cf8
• https://github.com/cloudflare/circl/releases/tag/v1.3.3
• https://github.com/advisories/GHSA-2q89-485c-9j2x