CVE-2025-7862
📋 TL;DR
This critical vulnerability in TOTOLINK T6 routers allows remote attackers to enable Telnet service without authentication by manipulating the telnet_enabled parameter. Affected systems are TOTOLINK T6 routers running firmware version 4.1.5cu.748_B20211015. The vulnerability exists in the setTelnetCfg function of the Telnet service component.
💻 Affected Systems
- TOTOLINK T6
📦 What is this software?
T6 Firmware by Totolink
⚠️ Risk & Real-World Impact
Worst Case
Remote attackers gain full administrative access to the router via Telnet, enabling complete device takeover, network traffic interception, lateral movement to internal networks, and persistent backdoor installation.
Likely Case
Attackers enable Telnet service remotely, gain administrative shell access, and use the compromised router as a foothold for further attacks on internal networks or for botnet recruitment.
If Mitigated
With proper network segmentation and access controls, impact is limited to the router itself, though attackers could still disrupt network connectivity or use the device for DDoS attacks.
🎯 Exploit Status
Proof-of-concept exploit code is publicly available on GitHub. The vulnerability requires a single HTTP request with specific parameters to enable Telnet without authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: Not available
Restart Required: No
Instructions:
No official patch is currently available. Monitor TOTOLINK's official website for firmware updates addressing CVE-2025-7862.
🔧 Temporary Workarounds
Disable Telnet Service
allManually disable Telnet service through the web interface if not required
Network Access Control
allBlock external access to port 80/443 on the router using firewall rules
🧯 If You Can't Patch
- Isolate affected routers in a separate VLAN with strict access controls
- Implement network monitoring for Telnet connection attempts and unusual HTTP requests to /cgi-bin/cstecgi.cgi
🔍 How to Verify
Check if Vulnerable:
Check if the router responds to HTTP POST requests to /cgi-bin/cstecgi.cgi with telnet_enabled parameter set to 1 without authenticationCheck Version:
Check firmware version in router web interface under System Status or via SSH/Telnet if already enabledVerify Fix Applied:
Attempt the exploit after applying workarounds - Telnet should not be enabled without proper authentication📡 Detection & Monitoring
Log Indicators:
- HTTP POST requests to /cgi-bin/cstecgi.cgi with telnet_enabled parameter
- Unexpected Telnet service startup
- Failed authentication attempts followed by successful Telnet connections
Network Indicators:
- Unexpected Telnet connections to router port 23
- HTTP requests with telnet_enabled=1 parameter from unusual sources
SIEM Query:
source_ip=* AND (url_path="/cgi-bin/cstecgi.cgi" AND parameters CONTAINS "telnet_enabled") OR (destination_port=23 AND protocol="telnet")🔗 References
- https://github.com/AnduinBrian/Public/blob/main/Totolink%20T6/Vuln/5.md
- https://github.com/AnduinBrian/Public/blob/main/Totolink%20T6/Vuln/5.md#poc-http
- https://vuldb.com/?ctiid.316975
- https://vuldb.com/?id.316975
- https://vuldb.com/?submit.617643
- https://www.totolink.net/
- https://www.youtube.com/watch?v=XeKu3tfeSME
- https://github.com/AnduinBrian/Public/blob/main/Totolink%20T6/Vuln/5.md
- https://github.com/AnduinBrian/Public/blob/main/Totolink%20T6/Vuln/5.md#poc-http
- https://www.youtube.com/watch?v=XeKu3tfeSME
