CVE-2021-30876
📋 TL;DR
CVE-2021-30876 is an out-of-bounds read vulnerability in AppleScript binary processing on macOS. Attackers can craft malicious AppleScript binaries to cause application crashes or leak process memory. This affects macOS Catalina, Big Sur, and Monterey users who process untrusted AppleScript files.
💻 Affected Systems
- macOS
📦 What is this software?
Macos by Apple
macOS is Apple's desktop and laptop operating system powering Mac computers used by millions of professionals, developers, creative professionals, and enterprise users worldwide. Built on a Unix foundation with the Darwin kernel and modern Cocoa frameworks, macOS delivers a seamless ecosystem integr...
Learn more about Macos →Macos by Apple
macOS is Apple's desktop and laptop operating system powering Mac computers used by millions of professionals, developers, creative professionals, and enterprise users worldwide. Built on a Unix foundation with the Darwin kernel and modern Cocoa frameworks, macOS delivers a seamless ecosystem integr...
Learn more about Macos →⚠️ Risk & Real-World Impact
Worst Case
Memory disclosure could expose sensitive information like passwords, encryption keys, or other process data to attackers, potentially enabling further exploitation.
Likely Case
Application crashes (denial of service) when processing malicious AppleScript binaries, disrupting workflow and productivity.
If Mitigated
With proper patching, no impact as the vulnerability is fully addressed in updated macOS versions.
🎯 Exploit Status
Exploitation requires user interaction to execute malicious AppleScript binaries, and successful memory disclosure requires additional steps to extract useful information.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: macOS Monterey 12.0.1, Security Update 2021-007 Catalina, macOS Big Sur 11.6.1
Vendor Advisory: https://support.apple.com/en-us/HT212869
Restart Required: Yes
Instructions:
1. Open System Preferences > Software Update. 2. Install available security updates. 3. Restart the system when prompted.
🔧 Temporary Workarounds
Disable AppleScript execution
allPrevent execution of AppleScript binaries through system policies or application restrictions
🧯 If You Can't Patch
- Restrict user permissions to prevent execution of untrusted AppleScript binaries
- Implement application whitelisting to block unauthorized AppleScript execution
🔍 How to Verify
Check if Vulnerable:
Check macOS version: if running Catalina, Big Sur, or Monterey without the specified security updates, the system is vulnerable.Check Version:
sw_versVerify Fix Applied:
Verify macOS version matches or exceeds Monterey 12.0.1, Catalina with Security Update 2021-007, or Big Sur 11.6.1.📡 Detection & Monitoring
Log Indicators:
- Unexpected application crashes when processing AppleScript files
- Console logs showing memory access violations
Network Indicators:
- No direct network indicators as exploitation is local
SIEM Query:
Search for process crashes related to AppleScript or osascript execution with error codes indicating memory access violations.