CVE-2021-20092
📋 TL;DR
This vulnerability allows unauthorized actors to access sensitive information through the web interfaces of affected Buffalo routers. It affects users of Buffalo WSR-2533DHPL2 and WSR-2533DHP3 routers with outdated firmware versions.
💻 Affected Systems
- Buffalo WSR-2533DHPL2
- Buffalo WSR-2533DHP3
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
An attacker could steal sensitive configuration data, credentials, or network information, potentially leading to full device compromise or network infiltration.
Likely Case
Unauthorized access to router settings or logs, enabling reconnaissance for further attacks or disruption of network services.
If Mitigated
If access controls are properly enforced, the impact is minimal as unauthorized requests are blocked.
🎯 Exploit Status
Exploitation involves simple HTTP requests to access restricted endpoints without authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: WSR-2533DHPL2 firmware > 1.02, WSR-2533DHP3 firmware > 1.24
Vendor Advisory: https://www.buffalo.jp/support/security/2021/wsr-2533dhpl2_wsr-2533dhp3.html
Restart Required: Yes
Instructions:
1. Download the latest firmware from Buffalo's official support site. 2. Log into the router's web interface. 3. Navigate to the firmware update section. 4. Upload and apply the new firmware file. 5. Reboot the router after update.
🔧 Temporary Workarounds
Disable web interface from WAN
allPrevent external access to the router's web management interface.
Log into router web interface, go to Advanced Settings > Security, disable remote management or restrict to LAN only.
Use firewall rules
allBlock inbound traffic to the router's web interface ports (typically 80/443).
Configure firewall to deny external access to router IP on ports 80 and 443.
🧯 If You Can't Patch
- Isolate the router on a separate network segment to limit exposure.
- Implement network monitoring to detect unauthorized access attempts.
🔍 How to Verify
Check if Vulnerable:
Check the firmware version in the router's web interface under System Information or similar section.Check Version:
Log into router web interface and navigate to System Status or use CLI if available: 'show version'.Verify Fix Applied:
After updating, confirm the firmware version is above the vulnerable thresholds and test access to restricted endpoints returns authentication errors.📡 Detection & Monitoring
Log Indicators:
- Unauthorized HTTP requests to sensitive endpoints like /cgi-bin/ or /admin/ in router logs.
Network Indicators:
- Unusual traffic patterns to router IP on port 80/443 from external sources.
SIEM Query:
source="router_logs" AND (url="*cgi-bin*" OR url="*admin*") AND response_code=200