CVE-2022-29245
Weak private key generation in SSH.NET
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| nuget | SSH.NET | < 2020.0.2 | 2020.0.2 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Ssh.Net Project | Ssh.Net | Versions 2020.0.0, 2020.0.1 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/sshnet/SSH.NET/blob/bc99ada7da3f05f50d9379f2644941d91d5bf05a/src/Renci.SshNet/Security/KeyExchangeECCurve25519.cs#L51
- https://github.com/sshnet/SSH.NET/commit/03c6d60736b8f7b42e44d6989a53f9b644a091fb
- https://github.com/sshnet/SSH.NET/releases/tag/2020.0.2
- https://github.com/sshnet/SSH.NET/security/advisories/GHSA-72p8-v4hg-v45p
- https://github.com/advisories/GHSA-72p8-v4hg-v45p
- https://nvd.nist.gov/vuln/detail/CVE-2022-29245
- https://github.com/sshnet/SSH.NET/commit/f1f273cf349532b9d41c1de51d3b83a9accedc88