CVE-2022-29245: SSH.NET Weak Private Key Generation Vulnerability

MODERATE
Advisory Identifier: GHSA-72p8-v4hg-v45p
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CVSS 6.5
CWE-338 CWE-330
Published
Advisory Summary

CVE-2022-29245 is a MODERATE (CVSS 6.5) weak private key generation vulnerability (CWE-338: Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)) affecting SSH.NET libraries in the NuGet ecosystem. The issue involves weak private key generation in ssh.net. Remediation is available by upgrading affected packages to version 2020.0.2.

CVE-2022-29245 at a Glance

CVE Identifier CVE-2022-29245
GHSA Identifier GHSA-72p8-v4hg-v45p
Severity MODERATE
CVSS v3.1 Base Score 6.5
CWE Classification CWE-338: Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)
Affected Product SSH.NET
Package Ecosystem NuGet
Published Date
Last Updated

Security Impact

CVSS: 6.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction Required (UI:R)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity None (I:N)
Availability None (A:N)

How to Fix CVE-2022-29245

To remediate this vulnerability, upgrade all affected SSH.NET dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

SSH.NET fixed: 2020.0.2 
Upgrade SSH.NET to 2020.0.2
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for SSH.NET

How to Check if You Are Affected

To determine whether your application is affected by CVE-2022-29245, inspect your project dependencies for SSH.NET:

inspect dependencies for SSH.NET

Analyze the terminal output to locate any version of SSH.NET in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2020.0.2), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-338: Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG), where the product uses a pseudo-random number generator (prng) in a security context, but the prng's algorithm is not cryptographically strong. In SSH.NET, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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.

CVE-2022-29245 Affected SSH.NET Versions

1 component(s)
Fixed Versions:
2020.0.2
Product / Package Ecosystem Affected Versions Fixed Version
SSH.NET
nuget/SSH.NET
NuGet
< 2020.0.2
2020.0.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/sshnet/SSH.NET/security/advisories/GHSA-72p8-v4hg-v45p
NVD — CVE-2022-29245 NVD
https://nvd.nist.gov/vuln/detail/CVE-2022-29245
Security Fix Commit FIX COMMIT
https://github.com/sshnet/SSH.NET/commit/03c6d60736b8f7b42e44d6989a53f9b644a091fb
Security Fix Commit FIX COMMIT
https://github.com/sshnet/SSH.NET/commit/f1f273cf349532b9d41c1de51d3b83a9accedc88
SSH.NET Source Repository REPOSITORY
https://github.com/sshnet/SSH.NET
SSH.NET Source Repository REPOSITORY
https://github.com/sshnet/SSH.NET/blob/bc99ada7da3f05f50d9379f2644941d91d5bf05a/src/Renci.SshNet/Security/KeyExchangeECCurve25519.cs#L51
SSH.NET Release RELEASE
https://github.com/sshnet/SSH.NET/releases/tag/2020.0.2

Frequently Asked Questions

What is CVE-2022-29245?
CVE-2022-29245 is a security vulnerability in SSH.NET involving Weak private key generation in SSH.NET under CWE-338: Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG).
Which SSH.NET versions are affected?
Affected versions include releases prior to 2020.0.2 across affected packages: SSH.NET.
What version fixes CVE-2022-29245?
Upgrading to 2020.0.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is SSH.NET affected?
Yes, SSH.NET is affected in releases prior to 2020.0.2. Upgrade your dependency to 2020.0.2 or later.
What is the CVSS score of CVE-2022-29245?
CVE-2022-29245 has a CVSS v3.1 base score of 6.5 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N.
What CWE is associated with CVE-2022-29245?
CVE-2022-29245 is classified under CWE-338: Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG) (The product uses a Pseudo-Random Number Generator (PRNG) in a security context, but the PRNG's algorithm is not cryptographically strong.).
How can I check NuGet dependencies for CVE-2022-29245?
Run the dependency tree command: 'inspect dependencies for SSH.NET'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-72p8-v4hg-v45p",
  "modified" : "2022-06-15T18:57:58Z",
  "published" : "2022-06-01T19:50:15Z",
  "aliases" : [ "CVE-2022-29245" ],
  "summary" : "Weak private key generation in SSH.NET",
  "details" : "During an **X25519** key exchange, the client’s private is generated with [**System.Random**](https://docs.microsoft.com/en-us/dotnet/api/system.random):\n\n```cs\nvar rnd = new Random();\n_privateKey = new byte[MontgomeryCurve25519.PrivateKeySizeInBytes];\nrnd.NextBytes(_privateKey);\n```\n\nSource: [KeyExchangeECCurve25519.cs](https://github.com/sshnet/SSH.NET/blob/bc99ada7da3f05f50d9379f2644941d91d5bf05a/src/Renci.SshNet/Security/KeyExchangeECCurve25519.cs#L51)  \nSource commit: https://github.com/sshnet/SSH.NET/commit/b58a11c0da55da1f5bad46faad2e9b71b7cb35b3\n\n[**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.\n\n### Impact\nWhen establishing an SSH connection to a remote host, during the X25519 key exchange, the private key is generated with\na weak random number generator whose seed can be bruteforced. This allows an attacker able to eavesdrop the\ncommunications to decrypt them.\n\n### Workarounds\nTo 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:\n```cs\nprivate static void RemoveUnsecureKEX(BaseClient client)\n{\n    client.ConnectionInfo.KeyExchangeAlgorithms.Remove(\"curve25519-sha256\");\n    client.ConnectionInfo.KeyExchangeAlgorithms.Remove(\"curve25519-sha256@libssh.org\");\n}\n```\n\n### Thanks\n\nThis issue was initially reported by **Siemens AG, Digital Industries**, shortly followed by @yaumn-synacktiv.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "SSH.NET"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2020.0.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/sshnet/SSH.NET/security/advisories/GHSA-72p8-v4hg-v45p"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2022-29245"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sshnet/SSH.NET/commit/03c6d60736b8f7b42e44d6989a53f9b644a091fb"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sshnet/SSH.NET/commit/f1f273cf349532b9d41c1de51d3b83a9accedc88"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/sshnet/SSH.NET"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sshnet/SSH.NET/blob/bc99ada7da3f05f50d9379f2644941d91d5bf05a/src/Renci.SshNet/Security/KeyExchangeECCurve25519.cs#L51"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sshnet/SSH.NET/releases/tag/2020.0.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-330", "CWE-338" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2022-06-01T19:50:15Z",
    "nvd_published_at" : "2022-05-31T17:15:00Z"
  }
}