CVE-2023-26421
📋 TL;DR
This CVE describes an integer underflow/wraparound vulnerability in Adobe Acrobat Reader that could allow arbitrary code execution when a user opens a malicious PDF file. Affected users include anyone running vulnerable versions of Adobe Acrobat Reader DC (Continuous) or 2020 Classic Track on Windows or macOS. Successful exploitation requires user interaction to open a malicious file.
💻 Affected Systems
- Adobe Acrobat Reader DC (Continuous Track)
- Adobe Acrobat Reader 2020 Classic Track
📦 What is this software?
Acrobat by Adobe
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with attacker gaining the same privileges as the current user, potentially leading to data theft, ransomware deployment, or persistent backdoor installation.
Likely Case
Local privilege escalation leading to malware installation, credential harvesting, or lateral movement within the network.
If Mitigated
Limited impact with proper application sandboxing and user privilege restrictions preventing system-wide compromise.
🎯 Exploit Status
Exploitation requires user interaction (opening malicious PDF). No public exploit code available at time of advisory.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: DC: 23.001.20174 or later; 2020 Classic: 20.005.30473 or later
Vendor Advisory: https://helpx.adobe.com/security/products/acrobat/apsb23-24.html
Restart Required: Yes
Instructions:
1. Open Adobe Acrobat Reader. 2. Go to Help > Check for Updates. 3. Follow prompts to install latest version. 4. Restart computer if required.
🔧 Temporary Workarounds
Disable JavaScript in Adobe Reader
allPrevents JavaScript-based exploitation vectors that might be used with this vulnerability
Edit > Preferences > JavaScript > Uncheck 'Enable Acrobat JavaScript'
Use Protected View
allOpen PDFs in Protected View to limit potential damage
File > Open > Check 'Open in Protected View' or enable in Preferences > Security (Enhanced)
🧯 If You Can't Patch
- Restrict PDF file opening to trusted sources only
- Implement application whitelisting to block unauthorized PDF execution
🔍 How to Verify
Check if Vulnerable:
Check Adobe Reader version: Help > About Adobe Acrobat Reader DC. If version is 23.001.20093 or earlier (DC) or 20.005.30441 or earlier (2020 Classic), you are vulnerable.Check 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 23.001.20174 or later (DC) or 20.005.30473 or later (2020 Classic) after update.📡 Detection & Monitoring
Log Indicators:
- Adobe Reader crash logs with memory access violations
- Unexpected child processes spawned from Adobe Reader
- Multiple failed PDF parsing attempts
Network Indicators:
- Outbound connections from Adobe Reader process to unknown IPs
- DNS requests for suspicious domains after PDF opening
SIEM Query:
process_name:"AcroRd32.exe" OR process_name:"AdobeReader" AND (event_type:crash OR parent_process:unexpected)