CVE-2020-7521
📋 TL;DR
This path traversal vulnerability in APC Easy UPS On-Line Software allows attackers to upload executable files to arbitrary directories by exploiting improper path validation in the FileUploadServlet. Attackers could achieve remote code execution on affected UPS management systems. Organizations using APC Easy UPS On-Line Software versions 2.0 and earlier are affected.
💻 Affected Systems
- APC Easy UPS On-Line Software
📦 What is this software?
Apc Easy Ups Online Software by Schneider Electric
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with remote code execution leading to ransomware deployment, data exfiltration, or lateral movement within the network.
Likely Case
Unauthorized file upload leading to web shell installation, persistence mechanisms, or service disruption of UPS management functions.
If Mitigated
Limited impact with proper network segmentation and file integrity monitoring detecting unauthorized file uploads.
🎯 Exploit Status
The vulnerability allows unauthenticated file upload to arbitrary locations, making exploitation straightforward. No public exploit code is documented, but the vulnerability type is well-understood.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 2.1 or later
Vendor Advisory: https://www.se.com/ww/en/download/document/SEVD-2020-224-04/
Restart Required: Yes
Instructions:
1. Download the updated software from Schneider Electric's website. 2. Uninstall the vulnerable version. 3. Install version 2.1 or later. 4. Restart the system to ensure all services use the patched version.
🔧 Temporary Workarounds
Network Access Control
allRestrict network access to the UPS management interface to only authorized administrative networks.
Web Application Firewall Rules
allImplement WAF rules to block path traversal patterns in file upload requests.
🧯 If You Can't Patch
- Isolate the UPS management system on a dedicated VLAN with strict firewall rules allowing only necessary administrative access.
- Implement file integrity monitoring on the system to detect unauthorized file uploads and changes to critical directories.
🔍 How to Verify
Check if Vulnerable:
Check the software version in the application interface or installation directory. Versions 2.0 or earlier are vulnerable.Check Version:
Check the application's About section or installation directory for version information. No standard command exists as this is a Windows application.Verify Fix Applied:
Verify the software version shows 2.1 or later after patching. Test the FileUploadServlet endpoint with path traversal attempts to confirm they are blocked.📡 Detection & Monitoring
Log Indicators:
- HTTP requests to FileUploadServlet with directory traversal sequences (../, ..\) in parameters
- Unexpected file creation in system directories
- Web shell or executable file uploads to non-standard locations
Network Indicators:
- POST requests to /FileUploadServlet with unusual file paths
- Outbound connections from the UPS management system to unexpected external IPs
SIEM Query:
source="web_server_logs" AND uri="/FileUploadServlet" AND (param="*../*" OR param="*..\\*")