CVE-2021-27197
📋 TL;DR
CVE-2021-27197 is an arbitrary file write vulnerability in Pelco Digital Sentry Server's DSUtility.dll component. It allows remote attackers to overwrite arbitrary files by crafting malicious HTML pages with VBScript. This affects organizations using vulnerable versions of Pelco Digital Sentry Server for video surveillance management.
💻 Affected Systems
- Pelco Digital Sentry Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise through overwriting critical system files, installation of persistent backdoors, or denial of service by corrupting essential files.
Likely Case
Data corruption, service disruption, or installation of malware on the Digital Sentry Server system.
If Mitigated
Limited impact if proper network segmentation and access controls prevent external exploitation attempts.
🎯 Exploit Status
Exploitation requires crafting HTML pages with specific VBScript to call the vulnerable AppendToTextFile method. Public proof-of-concept details are available in security advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 7.19.67 or later
Vendor Advisory: https://support.pelco.com/s/article/What-is-the-Digital-Sentry-software-release-revision-history
Restart Required: Yes
Instructions:
1. Download Digital Sentry Server version 7.19.67 or later from Pelco support portal. 2. Backup current configuration and data. 3. Run the installer to upgrade. 4. Restart the server and verify functionality.
🔧 Temporary Workarounds
Network Segmentation
allIsolate Digital Sentry Server from untrusted networks and restrict access to authorized users only.
Disable Scripting in Web Interface
windowsConfigure web server or application to block VBScript execution if possible (may impact legitimate functionality).
🧯 If You Can't Patch
- Implement strict network access controls to limit which systems can communicate with the Digital Sentry Server.
- Monitor for unusual file modification activities and HTML/VBScript requests to the server.
🔍 How to Verify
Check if Vulnerable:
Check the Digital Sentry Server version in the application interface or via Windows Programs and Features. If version is below 7.19.67, the system is vulnerable.Check Version:
Check via Digital Sentry Server GUI or examine installed programs in Windows Control Panel.Verify Fix Applied:
After patching, verify the version shows 7.19.67 or higher and test that the AppendToTextFile functionality now properly validates callers.📡 Detection & Monitoring
Log Indicators:
- Unusual file write operations in system logs
- HTML or VBScript requests containing 'AppendToTextFile' method calls
- Unexpected file modifications in Digital Sentry directories
Network Indicators:
- HTTP requests containing VBScript payloads targeting the Digital Sentry Server
- Unusual outbound connections from the server post-exploitation
SIEM Query:
source="DigitalSentry" AND (method="AppendToTextFile" OR user_agent CONTAINS "vbscript")🔗 References
- https://github.com/vitorespf/Advisories/blob/master/Pelco_Digital_Sentry_Server_AFW.txt
- https://support.pelco.com/s/article/What-is-the-Digital-Sentry-software-release-revision-history
- https://github.com/vitorespf/Advisories/blob/master/Pelco_Digital_Sentry_Server_AFW.txt
- https://support.pelco.com/s/article/What-is-the-Digital-Sentry-software-release-revision-history
