CVE-2022-29245

SSH.NET is a Secure Shell (SSH) library for .NET. In versions 2020.0.0 and 2020.0.1, during an `X25519` key exchange, the client’s private key is generated with `System.Random`. `System.Random` is not a cryptographically secure random number generator, it must therefore not be used for cryptographic purposes. 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 brute forced. This allows an attacker who is able to eavesdrop on the communications to decrypt them. Version 2020.0.2 contains a patch for this issue. As a workaround, one may disable support for `curve25519-sha256` and `curve25519-sha256@libssh.org` key exchange algorithms.

SSH.NET is a Secure Shell (SSH) library for .NET. In versions 2020.0.0 and 2020.0.1, during an `X25519` key exchange, the client’s private key is generated with `System.Random`. `System.Random` is not a cryptographically secure random number generator, it must therefore not be used for cryptographic purposes. 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 brute forced. This allows an attacker who is able to eavesdrop on the communications to decrypt them. Version 2020.0.2 contains a patch for this issue. As a workaround, one may disable support for `curve25519-sha256` and `curve25519-sha256@libssh.org` key exchange algorithms.

During an **X25519** key exchange, the client’s private is generated with [**System.Random**](https://docs.microsoft.com/en-us/dotnet/api/system.random): ```cs var rnd = new Random(); _privateKey = new byte[MontgomeryCurve25519.PrivateKeySizeInBytes]; rnd.NextBytes(_privateKey); ``` Source: [KeyExchangeECCurve25519.cs](https://github.com/sshnet/SSH.NET/blob/bc99ada7da3f05f50d9379f2644941d91d5bf05a/src/Renci.SshNet/Security/KeyExchangeECCurve25519.cs#L51) Source commit: https://github.com/sshnet/SSH.NET/commit/b58a11c0da55da1f5bad46faad2e9b71b7cb35b3 [**System.Random**](https://docs.microsoft.com/en-us/dotnet/api/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 `curve25519-sha256@libssh.org` 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("curve25519-sha256@libssh.org"); } ``` ### Thanks This issue was initially reported by **Siemens AG, Digital Industries**, shortly followed by @yaumn-synacktiv.

During an **X25519** key exchange, the client’s private is generated with [**System.Random**](https://docs.microsoft.com/en-us/dotnet/api/system.random): ```cs var rnd = new Random(); _privateKey = new byte[MontgomeryCurve25519.PrivateKeySizeInBytes]; rnd.NextBytes(_privateKey); ``` Source: [KeyExchangeECCurve25519.cs](https://github.com/sshnet/SSH.NET/blob/bc99ada7da3f05f50d9379f2644941d91d5bf05a/src/Renci.SshNet/Security/KeyExchangeECCurve25519.cs#L51) Source commit: https://github.com/sshnet/SSH.NET/commit/b58a11c0da55da1f5bad46faad2e9b71b7cb35b3 [**System.Random**](https://docs.microsoft.com/en-us/dotnet/api/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 `curve25519-sha256@libssh.org` 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("curve25519-sha256@libssh.org"); } ``` ### Thanks This issue was initially reported by **Siemens AG, Digital Industries**, shortly followed by @yaumn-synacktiv.

SSH.NET es una biblioteca de Secure Shell (SSH) para .NET. En versiones 2020.0.0 y 2020.0.1, durante un intercambio de claves "X25519", la clave privada del cliente se genera con "System.Random". "System.Random" no es un generador de números aleatorios criptográficamente seguro, por lo que no debe ser usado con fines criptográficos. Cuando es establecida una conexión SSH con un host remoto, durante el intercambio de claves X25519, la clave privada es generada con un generador de números aleatorios débil cuya semilla puede ser forzada. Esto permite que un atacante que sea capaz de espiar las comunicaciones las descifre. La versión 2020.0.2 contiene un parche para este problema. Como mitigación, puede deshabilitarse el soporte para los algoritmos de intercambio de claves "curve25519-sha256" y "curve25519-sha256@libssh.org"