CVE-2021-21796
📋 TL;DR
A use-after-free vulnerability in Nitro Pro PDF's JavaScript engine allows remote code execution when a user opens a malicious PDF document. This affects users of vulnerable Nitro Pro PDF versions, potentially enabling attackers to execute arbitrary code with the application's privileges.
💻 Affected Systems
- Nitro Pro PDF
📦 What is this software?
Nitro Pro by Gonitro
Nitro Pro by Gonitro
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise via arbitrary code execution with the privileges of the Nitro Pro PDF application, potentially leading to data theft, ransomware deployment, or lateral movement.
Likely Case
Malicious PDF documents delivered via phishing or compromised websites lead to code execution, enabling credential theft, malware installation, or data exfiltration.
If Mitigated
With proper patching and security controls, impact is limited to application crashes or denial of service without code execution.
🎯 Exploit Status
Exploitation requires user interaction to open a malicious PDF, but the vulnerability is reliably exploitable for code execution.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 13.31.0.605 and later
Vendor Advisory: https://www.gonitro.com/nps/security/updates
Restart Required: Yes
Instructions:
1. Open Nitro Pro PDF. 2. Go to Help > Check for Updates. 3. Follow prompts to install version 13.31.0.605 or later. 4. Restart the application.
🔧 Temporary Workarounds
Disable JavaScript in Nitro Pro PDF
windowsPrevents exploitation by disabling JavaScript execution in PDF documents.
Open Nitro Pro PDF > File > Preferences > Security > Uncheck 'Enable JavaScript'
Block PDF files at network perimeter
allPrevent delivery of malicious PDFs via email or web downloads.
🧯 If You Can't Patch
- Implement application whitelisting to block unauthorized executables from Nitro Pro PDF process.
- Use endpoint detection and response (EDR) to monitor for suspicious process creation from Nitro Pro PDF.
🔍 How to Verify
Check if Vulnerable:
Check Nitro Pro PDF version in Help > About. If version is below 13.31.0.605, the system is vulnerable.Check Version:
Not applicable - check via GUI in Help > AboutVerify Fix Applied:
Confirm version is 13.31.0.605 or higher in Help > About after patching.📡 Detection & Monitoring
Log Indicators:
- Application crashes of Nitro Pro PDF with memory access violations
- Unusual process creation from nitro_pro.exe
Network Indicators:
- Downloads of PDF files from suspicious sources followed by Nitro Pro PDF execution
SIEM Query:
Process creation where parent_process_name contains 'nitro_pro.exe' AND (process_name contains 'cmd.exe' OR process_name contains 'powershell.exe')