AIKIDO-2026-477741
russh is vulnerable to Use of a Broken or Risky Cryptographic Algorithm
43
Medium Risk
This Affects:
russhTL;DR
russh implements a hybrid ML-KEM 768 + X25519 key exchange in hybrid_mlkem.rs that does not validate the remote peer's X25519 public value before combining it into the shared secret. A peer can send an all-zero X25519 point alongside a valid ML-KEM encapsulation key, nullifying the X25519 contribution and downgrading the exchange to rely on ML-KEM alone. This weakens the classical half of the post-quantum hybrid guarantee for that session. The fix rejects zero and other low-order X25519 points during the hybrid exchange, matching the check already used in the standalone Curve25519 code.
Who does this affect?
You are affected if you are using a version that falls within the vulnerable range and your deployment negotiates the hybrid ML-KEM 768 with X25519 key exchange.
Background info
russh is vulnerable to Use of a Broken or Risky Cryptographic Algorithm in versions 0.0.1 - 0.62.7.
How to fix this
Upgrade the russh library to the patch version.
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