CVE-2021-21037
📋 TL;DR
This CVE describes a path traversal vulnerability in Adobe Acrobat Reader DC that allows arbitrary code execution. An unauthenticated attacker can exploit it by tricking a user into opening a malicious PDF file, potentially compromising the user's system. Affected versions include multiple release branches of Acrobat Reader DC.
💻 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 machine in the context of the current user, potentially leading to data theft, ransomware deployment, or lateral movement.
Likely Case
Malicious actor executes arbitrary code on the victim's system, installing malware, stealing credentials, or establishing persistence for further attacks.
If Mitigated
With proper controls like application whitelisting and least privilege, impact is limited to the user's context with restricted access to critical system resources.
🎯 Exploit Status
Exploitation requires social engineering to get user to open malicious PDF. No authentication needed once file is opened.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2020.013.20074 (or later), 2020.001.30018 (or later), 2017.011.30188 (or later) depending on branch
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 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 restrict file capabilities
File > Properties > Security > Enable Protected View for all files
🧯 If You Can't Patch
- Implement application whitelisting to prevent unauthorized executables from running
- Restrict user privileges to standard user accounts (not administrator)
🔍 How to Verify
Check if Vulnerable:
Check Adobe Reader version in Help > About Adobe Acrobat Reader DC and compare with affected versionsCheck Version:
On Windows: wmic product where name="Adobe Acrobat Reader DC" get versionVerify Fix Applied:
Verify version is updated beyond affected versions listed in advisory📡 Detection & Monitoring
Log Indicators:
- Unusual process creation from Adobe Reader (acrord32.exe)
- Suspicious file access patterns in system logs
- Unexpected network connections from Adobe Reader process
Network Indicators:
- Outbound connections from Adobe Reader to unknown IPs
- DNS requests for suspicious domains from user workstations
SIEM Query:
Process Creation where Image contains "acrord32.exe" and CommandLine contains unusual parameters