CVE-2025-3664
📋 TL;DR
This critical vulnerability in TOTOLINK A3700R routers allows attackers to bypass access controls on the setWiFiEasyGuestCfg function via the /cgi-bin/cstecgi.cgi endpoint. Attackers can exploit this remotely without authentication to modify guest WiFi settings or potentially gain further access. All users running the affected firmware version are vulnerable.
💻 Affected Systems
- TOTOLINK A3700R
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of the router allowing configuration changes, network traffic interception, or serving as a pivot point to attack internal network devices.
Likely Case
Unauthorized modification of guest WiFi settings, potential denial of service, or exposure of network credentials.
If Mitigated
No impact if the vulnerable endpoint is properly firewalled or the device is not internet-facing.
🎯 Exploit Status
Exploit details are publicly disclosed and require minimal technical skill to execute. The vendor has not responded to disclosure attempts.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: https://www.totolink.net/
Restart Required: No
Instructions:
No official patch is available. Monitor the vendor website for firmware updates and apply immediately when released.
🔧 Temporary Workarounds
Block CGI endpoint access
linuxUse firewall rules to block external access to /cgi-bin/cstecgi.cgi on the router.
iptables -A INPUT -p tcp --dport 80 -m string --string "/cgi-bin/cstecgi.cgi" --algo bm -j DROP
iptables -A INPUT -p tcp --dport 443 -m string --string "/cgi-bin/cstecgi.cgi" --algo bm -j DROP
Disable guest WiFi
allTurn off guest WiFi functionality to remove the vulnerable feature.
🧯 If You Can't Patch
- Isolate the router on a dedicated network segment with strict firewall rules limiting inbound and outbound traffic.
- Replace the vulnerable device with a different model or from a different vendor that provides security updates.
🔍 How to Verify
Check if Vulnerable:
Check router web interface or SSH/Telnet for firmware version. If version is 9.1.2u.5822_B20200513, device is vulnerable.Check Version:
telnet [router_ip] 80 then GET / HTTP/1.0\n\n or check web admin interface under System Info.Verify Fix Applied:
Verify firmware version has changed from 9.1.2u.5822_B20200513 after update. Test if /cgi-bin/cstecgi.cgi endpoint still responds to unauthorized requests.📡 Detection & Monitoring
Log Indicators:
- HTTP POST requests to /cgi-bin/cstecgi.cgi with setWiFiEasyGuestCfg parameter from unauthorized IPs
- Unusual guest WiFi configuration changes in system logs
Network Indicators:
- Unexpected traffic to router port 80/443 from external IPs
- Spike in requests to CGI endpoint
SIEM Query:
source="router_logs" AND (uri_path="/cgi-bin/cstecgi.cgi" AND method="POST" AND (src_ip NOT IN internal_networks))🔗 References
- https://lavender-bicycle-a5a.notion.site/TOTOLINK-A3700R-setWiFiEasyGuestCfg-1cb53a41781f805f9ee3f1b2d362d3f2?pvs=4
- https://vuldb.com/?ctiid.304842
- https://vuldb.com/?id.304842
- https://vuldb.com/?submit.551296
- https://www.totolink.net/
- https://lavender-bicycle-a5a.notion.site/TOTOLINK-A3700R-setWiFiEasyGuestCfg-1cb53a41781f805f9ee3f1b2d362d3f2
