CVE-2021-40731
📋 TL;DR
This vulnerability allows arbitrary code execution when a user opens a malicious JPEG2000 file in vulnerable Adobe Acrobat Reader versions. Attackers can exploit this out-of-bounds write vulnerability to run code with the current user's privileges. All users running affected Adobe Acrobat Reader DC versions 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 and user privileges.
Likely Case
Malware installation, data theft, or ransomware deployment through crafted PDF files containing malicious JPEG2000 images.
If Mitigated
Limited impact if user doesn't open untrusted files, but still vulnerable to targeted attacks.
🎯 Exploit Status
Requires user to open malicious file. No public exploit code known at advisory publication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Update to 21.007.20099 or later for 21.x, 20.004.30018 or later for 20.x, 17.011.30204 or later for 17.x
Vendor Advisory: https://helpx.adobe.com/security/products/acrobat/apsb21-104.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 computer if required.
🔧 Temporary Workarounds
Disable JPEG2000 image rendering
windowsPrevent Reader from processing JPEG2000 images by modifying registry settings
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Adobe\Acrobat Reader\DC\JPEG2000]
"bLoadJPX"=dword:00000000
Use Protected View
allConfigure Reader to open all PDFs from untrusted sources in Protected View mode
Edit preferences: Edit > Preferences > Security (Enhanced) > Enable Protected View at startup
🧯 If You Can't Patch
- Block all PDF files containing JPEG2000 images at network perimeter
- Implement application whitelisting to prevent unauthorized code execution
🔍 How to Verify
Check if Vulnerable:
Check Help > About Adobe Acrobat Reader DC and compare version against affected rangesCheck Version:
On Windows: wmic product where "name like 'Adobe Acrobat Reader DC%'" get versionVerify Fix Applied:
Verify version is 21.007.20099+, 20.004.30018+, or 17.011.30204+ after update📡 Detection & Monitoring
Log Indicators:
- Application crashes in Acrobat Reader with JPEG2000 processing errors
- Unexpected child processes spawned from Acrobat Reader
Network Indicators:
- Downloads of PDF files with JPEG2000 images from untrusted sources
SIEM Query:
EventID=1000 OR EventID=1001 AND SourceName="Application Error" AND ProcessName="AcroRd32.exe"