CVE-2021-30786
📋 TL;DR
A race condition vulnerability in Apple's PDF handling allows malicious PDF files to cause application crashes or execute arbitrary code. This affects iOS and macOS users who open untrusted PDF files before updating to patched versions.
💻 Affected Systems
- iOS
- 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 →⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with the privileges of the PDF viewer application, potentially leading to full system compromise.
Likely Case
Application crashes (denial of service) when opening malicious PDFs, with occasional successful code execution.
If Mitigated
No impact if systems are patched or if PDF files are opened in sandboxed environments.
🎯 Exploit Status
Exploitation requires user interaction to open a malicious PDF file. Race conditions can be challenging to exploit reliably.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: iOS 14.7, macOS Big Sur 11.5
Vendor Advisory: https://support.apple.com/en-us/HT212601
Restart Required: Yes
Instructions:
1. Open Settings app (iOS) or System Preferences (macOS). 2. Navigate to General > Software Update. 3. Download and install iOS 14.7 or macOS Big Sur 11.5. 4. Restart device after installation.
🔧 Temporary Workarounds
Disable automatic PDF opening
allConfigure systems to not automatically open PDF files from untrusted sources.
Use alternative PDF viewers
allOpen PDF files in third-party PDF viewers that are not affected by this vulnerability.
🧯 If You Can't Patch
- Block PDF file attachments at email gateways and web proxies
- Educate users to avoid opening PDF files from untrusted sources
🔍 How to Verify
Check if Vulnerable:
Check iOS version in Settings > General > About > Version. Check macOS version in Apple menu > About This Mac.Check Version:
iOS: Settings > General > About > Version. macOS: sw_versVerify Fix Applied:
Verify version is iOS 14.7 or later, or macOS Big Sur 11.5 or later.📡 Detection & Monitoring
Log Indicators:
- Application crash logs for PDF-related processes
- Unexpected process spawning from PDF viewers
Network Indicators:
- PDF file downloads from suspicious sources
- Unusual outbound connections after PDF opening
SIEM Query:
source="application.log" AND (process="Preview" OR process="Safari") AND event="crash"