CVE-2021-26087
📋 TL;DR
This vulnerability allows attackers to inject malicious scripts into the FortiWLC web interface, which are then executed when other users view the affected pages. Both authenticated remote attackers and unauthenticated attackers on the same network can exploit this stored cross-site scripting (XSS) vulnerability. The attack can lead to session hijacking, credential theft, or unauthorized actions on behalf of legitimate users.
💻 Affected Systems
- FortiWLC
📦 What is this software?
Fortiwlc by Fortinet
Fortiwlc by Fortinet
Fortiwlc by Fortinet
Fortiwlc by Fortinet
⚠️ Risk & Real-World Impact
Worst Case
Attackers could steal administrator credentials, hijack sessions, perform unauthorized configuration changes, or deploy malware to users accessing the management interface.
Likely Case
Attackers steal session cookies or credentials to gain unauthorized access to the management interface, potentially leading to network configuration changes or further attacks.
If Mitigated
With proper network segmentation and access controls, impact is limited to potential session hijacking within the management interface.
🎯 Exploit Status
Stored XSS vulnerabilities are commonly exploited. Attack requires network access to the appliance.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 8.6.1, 8.5.4, 8.4.9, 8.3.4
Vendor Advisory: https://fortiguard.fortinet.com/psirt/FG-IR-20-137
Restart Required: Yes
Instructions:
1. Download appropriate firmware version from Fortinet support portal. 2. Backup current configuration. 3. Upload and install new firmware via web interface or CLI. 4. Reboot appliance after installation.
🔧 Temporary Workarounds
Network Segmentation
allRestrict access to FortiWLC management interface to trusted networks only.
Access Control Lists
allImplement firewall rules to limit access to FortiWLC web interface.
🧯 If You Can't Patch
- Implement strict network segmentation to isolate FortiWLC management interface
- Deploy web application firewall (WAF) with XSS protection rules
🔍 How to Verify
Check if Vulnerable:
Check FortiWLC firmware version via web interface (System > Status) or CLI command 'show version'Check Version:
show versionVerify Fix Applied:
Verify firmware version is 8.6.1, 8.5.4, 8.4.9, or 8.3.4 or later📡 Detection & Monitoring
Log Indicators:
- Unusual JavaScript payloads in web interface logs
- Multiple failed login attempts followed by successful login from different IP
Network Indicators:
- Unusual HTTP POST requests containing script tags to FortiWLC interface
- Traffic patterns suggesting credential harvesting
SIEM Query:
source="fortiwlc" AND (http_method="POST" AND (uri="*<script>*" OR uri="*javascript:*"))