CVE-2021-28634
📋 TL;DR
This vulnerability allows authenticated attackers to execute arbitrary code on systems running vulnerable versions of Adobe Acrobat Reader DC by tricking users into opening malicious PDF files. The attacker gains code execution in the context of the current user, potentially leading to full system compromise. All users of affected Adobe Acrobat Reader DC versions are at risk.
💻 Affected Systems
- Adobe Acrobat Reader DC
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system takeover with attacker gaining the same privileges as the logged-in user, potentially leading to data theft, ransomware deployment, or lateral movement within the network.
Likely Case
Malware installation or data exfiltration after a user opens a malicious PDF document, with the attacker operating within the user's privilege context.
If Mitigated
No impact if patched versions are deployed or if users avoid opening untrusted PDF files.
🎯 Exploit Status
Exploitation requires authenticated access and user interaction (victim must open malicious file). The vulnerability is an OS command injection (CWE-78).
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2021.005.20055 or later for 2021 branch, 2020.004.30006 or later for 2020 branch, 2017.011.30198 or later for 2017 branch
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 for untrusted files
allOpens PDFs in sandboxed mode to limit potential damage
File > Properties > Security > Enable Protected View for files from potentially unsafe locations
🧯 If You Can't Patch
- Restrict user permissions to limit damage from successful exploitation
- Implement application whitelisting to prevent unauthorized executables from running
🔍 How to Verify
Check if Vulnerable:
Check Adobe Acrobat Reader DC version via Help > About Adobe Acrobat Reader DC and compare against affected versionsCheck Version:
On Windows: wmic product where name="Adobe Acrobat Reader DC" get versionVerify 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
- Suspicious command execution events originating from Adobe Reader processes
Network Indicators:
- Unexpected outbound connections from systems after PDF file opening
- DNS queries to suspicious domains following PDF access
SIEM Query:
Process creation where parent_process contains "AcroRd32.exe" or "Acrobat.exe" and process_name not in (allowed_reader_processes)