CVE-2021-40724
📋 TL;DR
A path traversal vulnerability in Adobe Acrobat Reader for Android allows attackers to execute arbitrary code by tricking users into opening malicious PDF files. This affects Android users running Acrobat Reader version 21.8.0 or earlier. Successful exploitation requires user interaction but grants code execution with the victim's permissions.
💻 Affected Systems
- Adobe Acrobat Reader for Android
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of the Android device, allowing data theft, surveillance, ransomware deployment, or persistence mechanisms installation.
Likely Case
Limited data exfiltration from the device or installation of secondary malware payloads after user opens a malicious PDF.
If Mitigated
No impact if users avoid opening untrusted PDFs or have updated to patched versions.
🎯 Exploit Status
Exploitation requires user interaction (opening malicious file) but no authentication. No public exploit code was available at disclosure.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 21.9.0 and later
Vendor Advisory: https://helpx.adobe.com/security/products/reader-mobile/apsb21-89.html
Restart Required: No
Instructions:
1. Open Google Play Store on Android device. 2. Search for Adobe Acrobat Reader. 3. Tap Update if available. 4. Ensure version is 21.9.0 or higher.
🔧 Temporary Workarounds
Disable PDF opening in Acrobat Reader
androidSet other PDF viewers as default to prevent Acrobat Reader from automatically opening PDF files
Restrict app permissions
androidRemove unnecessary permissions from Acrobat Reader to limit potential damage
🧯 If You Can't Patch
- Block PDF downloads from untrusted sources via email/web filtering
- Educate users to never open PDFs from unknown senders
🔍 How to Verify
Check if Vulnerable:
Check Acrobat Reader version in Android app settings. If version is 21.8.0 or earlier, device is vulnerable.Check Version:
No command line option. Check via Android Settings > Apps > Adobe Acrobat Reader > App InfoVerify Fix Applied:
Confirm Acrobat Reader version is 21.9.0 or higher in app settings.📡 Detection & Monitoring
Log Indicators:
- Unusual file access patterns in Acrobat Reader logs
- PDF files with unusual paths or names being processed
Network Indicators:
- PDF downloads from suspicious sources followed by unusual outbound connections
SIEM Query:
source="android_logs" app="com.adobe.reader" (event="file_access" AND path CONTAINS "../")