CVE-2021-27522
📋 TL;DR
CVE-2021-27522 is a privilege escalation vulnerability in Learnsite 1.2.5.0 that allows attackers to gain administrator access by manipulating user cookie values. Attackers can modify the first letter of a user cookie key to obtain administrator cookie keys, bypassing authentication controls. This affects all Learnsite 1.2.5.0 installations with default configurations.
💻 Affected Systems
- Learnsite
📦 What is this software?
Learnsite by Learnsite Project
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise where attackers gain administrative control, allowing them to modify all site content, access sensitive user data, and potentially execute arbitrary code on the server.
Likely Case
Attackers gain administrative privileges to the Learnsite platform, enabling them to modify course content, access student/teacher data, and manipulate system settings.
If Mitigated
Limited impact with proper network segmentation, strong authentication controls, and monitoring that detects unusual administrative activity.
🎯 Exploit Status
Exploitation requires a valid user account to obtain initial cookie, but the privilege escalation technique is simple and well-documented in public repositories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.2.5.1 or later
Vendor Advisory: https://github.com/WaterCountry/Learnsite/issues/1
Restart Required: Yes
Instructions:
1. Backup current installation. 2. Download and install Learnsite version 1.2.5.1 or later from official repository. 3. Restart the web application service. 4. Verify the fix by testing authentication functionality.
🔧 Temporary Workarounds
Cookie Validation Enhancement
allImplement additional server-side cookie validation to detect and reject manipulated cookie keys
Modify JudgIsAdmin() function in /Manager/index.aspx to include cryptographic validation of cookie keys
Network Access Restriction
allRestrict access to the /Manager/ directory to trusted IP addresses only
# Apache: Order deny,allow
Deny from all
Allow from 192.168.1.0/24
# Nginx: allow 192.168.1.0/24;
deny all;
# IIS: Use IP restrictions in IIS Manager
🧯 If You Can't Patch
- Implement Web Application Firewall (WAF) rules to detect and block cookie manipulation attempts
- Enable detailed logging of authentication events and monitor for unusual privilege escalation patterns
🔍 How to Verify
Check if Vulnerable:
Check if running Learnsite version 1.2.5.0 by examining the application version in the admin interface or checking the installation directory for version markers.Check Version:
Check the web interface footer or examine the web.config/version.txt file in the Learnsite installation directory.Verify Fix Applied:
After patching, attempt to reproduce the vulnerability by modifying a user cookie's first character and verifying that administrator access is not granted.📡 Detection & Monitoring
Log Indicators:
- Multiple failed authentication attempts followed by successful admin login from same IP
- Unusual cookie values in access logs
- Administrative actions from previously non-admin users
Network Indicators:
- HTTP requests to /Manager/index.aspx with modified cookie parameters
- Rapid privilege escalation attempts
SIEM Query:
source="web_logs" AND (uri="/Manager/index.aspx" AND cookie CONTAINS "modified_key" OR "JudgIsAdmin" AND status=200)