CVE-2026-73430 Russh: Pre-auth remote panic via all-zero Curve25519 peer public value (encode_mpint OOB)

Russh is a Rust SSH client & server library. Prior to 0.62.4, an unauthenticated SSH client can cause a denial of service by sending SSHMSGKEXECDHINIT with a 32-byte all-zero QC value. Curve25519Kex::serverdh in russh/src/kex/curve25519.rs accepts the all-zero peer public value and computes an...