CVE-2021-28642
📋 TL;DR
This CVE describes an out-of-bounds write vulnerability in Adobe Acrobat Reader DC that allows arbitrary code execution when a user opens a malicious PDF file. Attackers can exploit this to run code with the victim's privileges, potentially compromising the entire system. All users running affected versions of Acrobat Reader DC are at risk.
💻 Affected Systems
- Adobe Acrobat Reader DC
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with attacker gaining full control of the victim's computer, data theft, ransomware deployment, and lateral movement within the network.
Likely Case
Malware installation leading to data exfiltration, credential theft, and persistence on the compromised system.
If Mitigated
Limited impact with proper application sandboxing and user privilege restrictions, potentially containing the exploit to the PDF reader process.
🎯 Exploit Status
Exploitation requires social engineering to trick users into opening malicious PDF files. No authentication is required once the file is opened.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2021.005.20055, 2020.004.30006, 2017.011.30198 or later
Vendor Advisory: https://helpx.adobe.com/security/products/acrobat/apsb21-51.html
Restart Required: Yes
Instructions:
1. Open Adobe Acrobat Reader DC. 2. Go to Help > Check for Updates. 3. Follow prompts to install available updates. 4. Restart the application when prompted.
🔧 Temporary Workarounds
Disable JavaScript in Adobe Reader
allPrevents JavaScript-based exploitation vectors that might be used in conjunction with this vulnerability
Edit > Preferences > JavaScript > Uncheck 'Enable Acrobat JavaScript'
Use Protected View
allOpen PDFs in Protected View mode to limit potential damage from malicious files
File > Properties > Security > Enable Protected View for all files from potentially unsafe locations
🧯 If You Can't Patch
- Implement application whitelisting to block unauthorized PDF readers
- Use network segmentation to isolate PDF processing systems from critical assets
🔍 How to Verify
Check if Vulnerable:
Check Adobe Acrobat Reader DC version via Help > About Adobe Acrobat Reader DCCheck Version:
Windows: wmic product where name="Adobe Acrobat Reader DC" get version
macOS: /Applications/Adobe\ Acrobat\ Reader\ DC.app/Contents/Info.plist | grep -A1 CFBundleShortVersionStringVerify Fix Applied:
Verify version is 2021.005.20055 or later, 2020.004.30006 or later, or 2017.011.30198 or later📡 Detection & Monitoring
Log Indicators:
- Unusual process creation from AcroRd32.exe or Acrobat.exe
- Multiple failed PDF parsing attempts
- Unexpected network connections from PDF reader process
Network Indicators:
- Outbound connections to suspicious domains after PDF opening
- Unusual DNS queries from PDF reader hosts
SIEM Query:
source="windows" AND process_name IN ("AcroRd32.exe", "Acrobat.exe") AND (parent_process!="explorer.exe" OR command_line CONTAINS "-Embedding")