GHSA-72p8-v4hg-v45p Weak private key generation in SSH.NET

• NuGet SSH.NET: < 2020.0.2 → fixed in 2020.0.2

During an X25519 key exchange, the client’s private is generated with System.Random: ```cs var rnd = new Random(); _privateKey = new byte[MontgomeryCurve25519.PrivateKeySizeInBytes]; rnd.NextBytes(_privateKey); ``` Source: KeyExchangeECCurve25519.cs Source commit: https://github.com/sshnet/SSH.NET/commit/b58a11c0da55da1f5bad46faad2e9b71b7cb35b3 System.Random is not a cryptographically secure random number generator, it must therefore not be used for cryptographic purposes. Impact When establishing an SSH connection to a remote host, during the X25519 key exchange, the private key is generated with a weak random number generator whose seed can be bruteforced. This allows an attacker able to eavesdrop the communications to decrypt them. Workarounds To ensure you're not affected by this vulnerability, you can disable support for `curve25519-sha256` and `[email protected]` key exchange algorithms by invoking the following method before a connection is established: ```cs private static void RemoveUnsecureKEX(BaseClient client) { client.ConnectionInfo.KeyExchangeAlgorithms.Remove("curve25519-sha256"); client.ConnectionInfo.KeyExchangeAlgorithms.Remove("[email protected]"); } ``` Thanks This issue was initially reported by Siemens AG, Digital Industries, shortly followed by @yaumn-synacktiv.