CVE-2021-21044
📋 TL;DR
CVE-2021-21044 is an out-of-bounds write vulnerability in Adobe Acrobat Reader DC that allows arbitrary code execution when parsing malicious JPEG files. Attackers can exploit this by tricking users into opening crafted PDF files containing malicious JPEG images. This affects users of Adobe Acrobat Reader DC across multiple versions on Windows, macOS, and potentially other platforms.
💻 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, enabling data theft, ransomware deployment, or persistent backdoor installation.
Likely Case
Malware installation leading to credential theft, data exfiltration, or system disruption, with the attacker operating in the context of the logged-in user's privileges.
If Mitigated
Limited impact with proper security controls - potentially isolated to sandboxed environment with minimal data access.
🎯 Exploit Status
Exploitation requires user interaction (opening malicious file). The vulnerability is in JPEG parsing within PDF files.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2020.013.20075, 2020.001.30019, 2017.011.30189 and later
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 available updates. 4. Restart the application after installation.
🔧 Temporary Workarounds
Disable JPEG rendering in PDFs
windowsPrevent JPEG image rendering in PDF documents through registry/configuration changes
Windows Registry: HKEY_CURRENT_USER\Software\Adobe\Acrobat Reader\DC\AVGeneral\bDisableJPEG=1
Use Protected View
allEnable Protected View for all files from potentially unsafe locations
Edit > Preferences > Security (Enhanced) > Enable Protected View at startup
🧯 If You Can't Patch
- Restrict user permissions to prevent execution of arbitrary code
- Implement application whitelisting to block unauthorized executables
🔍 How to Verify
Check if Vulnerable:
Check Adobe Acrobat Reader DC version via Help > About Adobe Acrobat Reader DCCheck Version:
Windows: "C:\Program Files\Adobe\Acrobat Reader DC\Reader\AcroRd32.exe" /? | find "Version"Verify Fix Applied:
Verify version is 2020.013.20075 or higher, 2020.001.30019 or higher, or 2017.011.30189 or higher📡 Detection & Monitoring
Log Indicators:
- Application crashes with memory access violations
- Unusual child processes spawned from AcroRd32.exe
Network Indicators:
- Unexpected outbound connections after PDF file opening
- DNS requests to suspicious domains post-PDF access
SIEM Query:
process_name:"AcroRd32.exe" AND (event_id:1000 OR event_id:1001) AND exception_code:0xc0000005