Weak private key generation in SSH.NET
During an X25519 key exchange, the client’s private is generated with System.Random:
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 curve25519-sha256@libssh.org key exchange algorithms by invoking the following method before a connection is established:
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 software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| .NET (NuGet) | SSH.NET | < 2020.0.2 | 2020.0.2 |
References
- https://github.com/sshnet/SSH.NET/security/advisories/GHSA-72p8-v4hg-v45p
- https://nvd.nist.gov/vuln/detail/CVE-2022-29245
- https://github.com/sshnet/SSH.NET/commit/03c6d60736b8f7b42e44d6989a53f9b644a091fb
- https://github.com/sshnet/SSH.NET/commit/f1f273cf349532b9d41c1de51d3b83a9accedc88
- https://github.com/sshnet/SSH.NET
- https://github.com/sshnet/SSH.NET/blob/bc99ada7da3f05f50d9379f2644941d91d5bf05a/src/Renci.SshNet/Security/KeyExchangeECCurve25519.cs#L51
- https://github.com/sshnet/SSH.NET/releases/tag/2020.0.2
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N- Weakness (CWE)
CWE-330, CWE-338- Platform
- .NET (NuGet)
- Package
SSH.NET- Disclosed
- 01.06.2022
- Updated
- 11.10.2026 11:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-72p8-v4hg-v45p - CC BY 4.0
Vulnerability history: SSH.NET
All published vulnerabilities of this package (.NET (NuGet)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 3
- First → latest
- 06.2022 09.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 2
- Medium 1
Disclosures per year
- 2022: 1
- 2023: 0
- 2024: 0
- 2025: 0
- 2026: 2
-
Weak private key generation in SSH.NET this entry
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