CVE-2021-28631
📋 TL;DR
This CVE describes a use-after-free vulnerability in Adobe Acrobat Reader DC that allows arbitrary code execution when a user opens a malicious PDF file. An unauthenticated attacker can exploit this to run code with the victim's privileges. Affected users include anyone running vulnerable versions of Acrobat Reader DC.
💻 Affected Systems
- Adobe Acrobat Reader DC
📦 What is this software?
Acrobat by Adobe
Acrobat by Adobe
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with attacker gaining full control of the victim's computer, data theft, ransomware deployment, or lateral movement within the network.
Likely Case
Malware installation leading to data exfiltration, credential theft, or system disruption for individual users who open malicious PDFs.
If Mitigated
Limited impact with proper application sandboxing, endpoint protection, and user awareness preventing malicious file execution.
🎯 Exploit Status
Exploitation requires user interaction (opening malicious file) but no authentication. Use-after-free vulnerabilities typically require specific memory manipulation.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2021.001.20156, 2020.001.30026, 2017.011.30197 or later
Vendor Advisory: https://helpx.adobe.com/security/products/acrobat/apsb21-37.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 PDFs
allPrevents JavaScript execution in PDF files which may reduce attack surface
Edit > Preferences > JavaScript > Uncheck 'Enable Acrobat JavaScript'
Use Protected View
allForce all PDFs to open in Protected View mode
Edit > Preferences > Security (Enhanced) > Check 'Enable Protected View at startup'
🧯 If You Can't Patch
- Implement application whitelisting to block unauthorized PDF readers
- Deploy endpoint detection and response (EDR) to monitor for suspicious PDF execution
🔍 How to Verify
Check if Vulnerable:
Check Help > About Adobe Acrobat Reader DC and compare version to affected rangesCheck Version:
On Windows: wmic product where name="Adobe Acrobat Reader DC" get versionVerify Fix Applied:
Verify version is 2021.001.20156+, 2020.001.30026+, or 2017.011.30197+📡 Detection & Monitoring
Log Indicators:
- Unexpected process creation from AcroRd32.exe
- Memory access violations in application logs
- PDF file execution followed by network connections
Network Indicators:
- Outbound connections from Acrobat Reader process to suspicious domains
- DNS requests for known exploit domains
SIEM Query:
process_name:"AcroRd32.exe" AND (event_id:4688 OR parent_process_name:"explorer.exe") AND command_line:"*.pdf"