CVE-2022-42789 - Improved Code Signature Validation in macOS Big Sur 11.7, macOS Ventura 13, and macOS Monterey 12.6

A recent vulnerability, identified as CVE-2022-42789, was found in macOS Big Sur 11.7, macOS Ventura 13, and Monterey 12.6. This vulnerability exposes user-sensitive data by exploiting a weakness in the code signature validation process. Apple has addressed this vulnerability by implementing improved signature checks to ensure the security and privacy of its users' data.

Background

Code signing is a critical security aspect in macOS that provides a layer of protection for users to ensure that the applications they are running are genuine and not tampered with. It validates the original creator of the app and guarantees the validity and integrity of the app's code.

The Vulnerability

CVE-2022-42789 was identified as an issue in the code signature validation process of macOS Big Sur 11.7, macOS Ventura 13, and macOS Monterey 12.6. It allows attackers to potentially access sensitive user information, such as personal data and credentials, by bypassing the usual code signing process. The potential exploit takes advantage of the weakened security validation checks within these versions of macOS.

The Solution

Apple has resolved this vulnerability by introducing additional signature checks, providing a considerable enhancement to the existing validation process. They released updates for macOS Big Sur 11.7, macOS Ventura 13, and macOS Monterey 12.6 that include these crucial security enhancements. Users should apply these updates immediately to protect against potential attacks.

Code snippet example

Here, we demonstrate how the improved checks in the updated macOS versions work by comparing a known-good code signature with a suspected tampered version:

// Example of expected (known-good) code signature:
{
  "CFBundleIdentifier": "com.example.MyApp",
  "TeamIdentifier": "ABCDEFG12345",
  "Authority": "Apple iPhone OS Application Signing",
  "InfoPlist": {
    "CFBundleShortVersionString": "1.",
    "CFBundleVersion": "1"
  },
  "CodeDirectory": {
    "CDHash": "a1b2c3d4e5f6g7h8i9j",
    // ... other entries ...
  }
}

// Example of tampered (bypassed) code signature:
{
  "CFBundleIdentifier": "com.example.MyApp",
  "TeamIdentifier": "ABCDEFG12345",
  "Authority": "Apple iPhone OS Application Signing",
  "InfoPlist": {
    "CFBundleShortVersionString": "1.",
    "CFBundleVersion": "1"
  },
  "CodeDirectory": {
    "CDHash": "x1y2z3a4b5c6d7e8f9",
    // ... other entries ...
  }
}

// Improved signature validation checks in the updated macOS versions:
function compareSignatures(originalSignature, potentialTamperedSignature) {
  if (originalSignature.CFBundleIdentifier !== potentialTamperedSignature.CFBundleIdentifier || originalSignature.TeamIdentifier !== potentialTamperedSignature.TeamIdentifier || originalSignature.Authority !== potentialTamperedSignature.Authority || originalSignature.InfoPlist.CFBundleShortVersionString !== potentialTamperedSignature.InfoPlist.CFBundleShortVersionString || originalSignature.InfoPlist.CFBundleVersion !== potentialTamperedSignature.InfoPlist.CFBundleVersion || originalSignature.CodeDirectory.CDHash !== potentialTamperedSignature.CodeDirectory.CDHash) {
    console.error('Code signature validation failed - potential tampering detected');
    return false;
  }
  return true;
}

In this example, the newly introduced checks enhance the signature validation process by comparing additional code signature properties, ensuring that the application's code has not been tampered with.

Relevant links

1. Apple Security Updates - macOS Big Sur 11.7, macOS Ventura 13, macOS Monterey 12.6
2. CVE-2022-42789 - National Vulnerability Database (NVD)
3. Apple Developer Documentation - Code Signing for macOS

Conclusion

CVE-2022-42789 exposes a critical vulnerability in macOS, but with the updated code signature validation measures in place, users should feel confident in the security of their data. As always, it is recommended to keep your macOS updated with the latest software to ensure that your system benefits from such security enhancements.

Timeline

Published on: 11/01/2022 20:15:00 UTC
Last modified on: 11/02/2022 19:12:00 UTC