Summary
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.
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:
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.
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.
Security-sensitive operations rely on values that are predictable or insufficiently random. Typical impact: forged tokens, guessable identifiers, or broken cryptographic protocols.
CVE-2022-29245 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2020.0.2); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2022-29245? CVE-2022-29245 is a medium-severity use of insufficiently random values vulnerability in SSH.NET (nuget), affecting versions < 2020.0.2. It is fixed in 2020.0.2. Security-sensitive operations rely on values that are predictable or insufficiently random.
- How severe is CVE-2022-29245? CVE-2022-29245 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of SSH.NET are affected by CVE-2022-29245? SSH.NET (nuget) versions < 2020.0.2 is affected.
- Is there a fix for CVE-2022-29245? Yes. CVE-2022-29245 is fixed in 2020.0.2. Upgrade to this version or later.
- Is CVE-2022-29245 exploitable, and should I be worried? Whether CVE-2022-29245 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2022-29245 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2022-29245? Upgrade
SSH.NETto 2020.0.2 or later.