CVE-2021-26605
📋 TL;DR
CVE-2021-26605 is an improper input validation vulnerability in ezPDFReader's JSON-RPC communication that allows remote attackers to execute arbitrary commands. This affects users of ezPDFReader who have the vulnerable service enabled. Attackers can exploit this by sending crafted JSON-RPC requests to the ezPDF launcher.
💻 Affected Systems
- ezPDFReader
📦 What is this software?
Ezpdfreader by Unidocs
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with attacker gaining complete control over the affected system, installing malware, stealing data, or using the system as a pivot point for further attacks.
Likely Case
Remote code execution leading to installation of ransomware, data exfiltration, or creation of a persistent backdoor on the compromised system.
If Mitigated
Limited impact if network segmentation restricts access to the vulnerable service and proper input validation is implemented.
🎯 Exploit Status
The vulnerability allows unauthenticated remote code execution through crafted JSON-RPC requests, making exploitation relatively straightforward for attackers with network access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Update to the latest version of ezPDFReader (specific version not specified in provided references)
Vendor Advisory: https://www.boho.or.kr/krcert/secNoticeView.do?bulletin_writing_sequence=36168
Restart Required: Yes
Instructions:
1. Download the latest version of ezPDFReader from the official vendor website. 2. Uninstall the current vulnerable version. 3. Install the updated version. 4. Restart the system to ensure all services are updated.
🔧 Temporary Workarounds
Disable ezPDFReader Service
windowsStop and disable the ezPDF launcher service to prevent JSON-RPC communication exploitation.
sc stop "ezPDFReader Service"
sc config "ezPDFReader Service" start= disabled
Network Segmentation
windowsBlock network access to the ezPDFReader service port using firewall rules.
netsh advfirewall firewall add rule name="Block ezPDFReader" dir=in action=block program="C:\Program Files\ezPDFReader\ezPDFReader.exe" enable=yes
🧯 If You Can't Patch
- Implement strict network segmentation to isolate systems running ezPDFReader from untrusted networks.
- Deploy application whitelisting to prevent execution of unauthorized binaries that might be dropped by attackers.
🔍 How to Verify
Check if Vulnerable:
Check if ezPDFReader is installed and running the vulnerable service version. Review system logs for JSON-RPC communication attempts to the ezPDF launcher.Check Version:
Check the version in ezPDFReader's About dialog or examine the executable properties in Windows Explorer.Verify Fix Applied:
Verify that ezPDFReader has been updated to the latest version and the service is no longer vulnerable by checking version information and monitoring for exploit attempts.📡 Detection & Monitoring
Log Indicators:
- Unusual JSON-RPC requests to the ezPDF launcher service
- Unexpected process creation from ezPDFReader.exe
- Failed authentication attempts to the ezPDF service
Network Indicators:
- Suspicious network traffic to the ezPDFReader service port
- Unexpected outbound connections from systems running ezPDFReader
SIEM Query:
source="windows" AND process_name="ezPDFReader.exe" AND (event_id=4688 OR event_id=1) AND command_line CONTAINS "powershell" OR command_line CONTAINS "cmd"