CVE-2021-21033
📋 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. All users running affected versions of Acrobat Reader DC are at risk.
💻 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, and 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 security controls - malware may be blocked by endpoint protection, and user account restrictions limit damage scope.
🎯 Exploit Status
Exploitation requires user interaction (opening malicious PDF). Attack vector is typically phishing emails with malicious attachments.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2020.013.20074 (or later), 2020.001.30018 (or later), 2017.011.30188 (or later) - update to latest available version
Vendor Advisory: https://helpx.adobe.com/security/products/acrobat/apsb21-09.html
Restart Required: Yes
Instructions:
1. Open Adobe Acrobat Reader DC. 2. Go to Help > Check for Updates. 3. Follow prompts to install latest version. 4. Restart computer if required.
🔧 Temporary Workarounds
Disable JavaScript in Adobe Reader
allPrevents JavaScript-based exploitation vectors
Edit > Preferences > JavaScript > Uncheck 'Enable Acrobat JavaScript'
Use Protected View
allOpen PDFs in protected mode to limit damage
File > Preferences > Security (Enhanced) > Enable Protected View for all files
🧯 If You Can't Patch
- Block PDF files at email gateways and web proxies
- Implement application whitelisting to prevent unauthorized executables
🔍 How to Verify
Check if Vulnerable:
Check Adobe Reader version in 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 updated beyond affected versions listed in advisory📡 Detection & Monitoring
Log Indicators:
- Adobe Reader crash logs with memory access violations
- Unexpected child processes spawned from AcroRd32.exe
Network Indicators:
- Outbound connections from Adobe Reader to suspicious domains
- DNS queries for known exploit kit domains
SIEM Query:
process_name:"AcroRd32.exe" AND (event_id:1000 OR parent_process:!"explorer.exe")