Memory Exhaustion vulnerability in the key exchange logic of the libssh library. When an authenticated client repeatedly performs rekeying with incorrect first_kex_packet_follows guesses, libssh allocates new ephemeral key pairs without freeing old ones stored in session->next_crypto. Over time, this results in a memory leak that can exhaust system memory and cause a client-side denial-of-service (DoS). This flaw affects several KEX algorithms (Curve25519, ECDH, sntrup761x25519, DH-GEX) across multiple crypto backends (libgcrypt, OpenSSL, mbedTLS). The issue requires an authenticated client and does not impact the server side.
Versions Affected : libssh >= 0.6.0