CVE-2021-28638
📋 TL;DR
This heap-based buffer overflow vulnerability in Adobe Acrobat Reader DC allows attackers to execute arbitrary code on affected systems. An unauthenticated attacker can exploit this by tricking a user into opening a malicious PDF file, potentially gaining the same privileges as the current user. Users of Adobe Acrobat Reader DC versions 2021.005.20054 and earlier, 2020.004.30005 and earlier, or 2017.011.30197 and earlier are affected.
💻 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 machine and potentially pivoting to other systems in the network.
Likely Case
Local privilege escalation leading to data theft, ransomware deployment, or installation of persistent backdoors on individual workstations.
If Mitigated
Limited impact with only application crash if exploit fails or security controls block execution.
🎯 Exploit Status
Exploitation requires user interaction (opening malicious PDF). The vulnerability is in the heap memory management, making reliable exploitation more complex than stack-based overflows.
🛠️ 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 limit lateral movement from compromised systems
🔍 How to Verify
Check if Vulnerable:
Check Adobe Reader version via Help > About Adobe Acrobat Reader DC and compare against affected versionsCheck 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 higher, 2020.004.30006 or higher, or 2017.011.30198 or higher📡 Detection & Monitoring
Log Indicators:
- Adobe Reader crash logs with heap corruption errors
- Unexpected child processes spawned from Adobe Reader
Network Indicators:
- Outbound connections from Adobe Reader process to unknown IPs
- DNS requests for suspicious domains from Adobe Reader
SIEM Query:
process_name:"AcroRd32.exe" AND (event_id:1000 OR event_id:1001) AND (exception_code:0xc0000005 OR exception_code:0xc0000409)