CVE-2024-39420
📋 TL;DR
This CVE describes a Time-of-check Time-of-use (TOCTOU) race condition vulnerability in Adobe Acrobat Reader that could allow arbitrary code execution when a user opens a malicious PDF file. Attackers can manipulate file resources between validation and use, potentially gaining control of the system. Users of affected Adobe Acrobat Reader versions are at risk.
💻 Affected Systems
- Adobe Acrobat Reader DC
- Adobe Acrobat Reader
📦 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, enabling data theft, ransomware deployment, or persistent backdoor installation.
Likely Case
Local privilege escalation or arbitrary code execution in the context of the current user, allowing file system access, credential theft, and lateral movement.
If Mitigated
No impact if users avoid opening untrusted PDF files and keep software updated.
🎯 Exploit Status
Exploitation requires user interaction (opening malicious file) and precise timing to win the race condition. No public exploit code available as of analysis.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Update to versions after those listed in affected versions (check Adobe advisory for specific patched versions)
Vendor Advisory: https://helpx.adobe.com/security/products/acrobat/apsb24-70.html
Restart Required: Yes
Instructions:
1. Open Adobe Acrobat Reader. 2. Go to Help > Check for Updates. 3. Follow prompts to download and install latest version. 4. Restart computer if required.
🔧 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 untrusted files
🧯 If You Can't Patch
- Restrict PDF file opening to trusted sources only using application whitelisting
- Implement network segmentation to limit lateral movement if exploitation occurs
🔍 How to Verify
Check if Vulnerable:
Check Adobe Acrobat Reader version in Help > About Adobe Acrobat Reader DC and compare with affected versions listCheck Version:
On Windows: wmic product where name="Adobe Acrobat Reader DC" get version
On macOS: /Applications/Adobe\ Acrobat\ Reader\ DC.app/Contents/Info.plist | grep -A1 CFBundleShortVersionStringVerify Fix Applied:
Verify version is newer than affected versions listed in CVE description and check that updates are applied successfully📡 Detection & Monitoring
Log Indicators:
- Unexpected process creation from AcroRd32.exe
- Suspicious file writes or registry modifications by Adobe Reader processes
- Crash logs from Adobe Reader with unusual error codes
Network Indicators:
- Outbound connections from Adobe Reader to unusual destinations
- DNS requests for suspicious domains from system running Adobe Reader
SIEM Query:
process_name:"AcroRd32.exe" AND (process_child_creation OR file_write OR registry_modification)