Russh: Unchecked CryptoVec allocation and growth handling is reachable from local agent inputs in current russh releases and from remote SSH traffic in historical pre-0.58.0 releases

Russh is a Rust SSH client & server library. Prior to version 0.60.3, CryptoVec used unchecked capacity growth, unchecked length arithmetic, and unsafe allocation/locking paths. In current russh releases, local SSH agent peers could still feed attacker-controlled frame lengths into buffer growth before validation. In older russh releases before 0.58.0, remote SSH traffic also reached CryptoVec through transport and compression buffers. This issue has been patched in version 0.60.3.