CVE-2025-4496
📋 TL;DR
A critical buffer overflow vulnerability in TOTOLINK routers allows remote attackers to execute arbitrary code by manipulating the FileName parameter in the CloudACMunualUpdate function. This affects multiple TOTOLINK router models running firmware version 4.1.8cu.5241_B20210927. Attackers can exploit this without authentication to potentially take full control of affected devices.
💻 Affected Systems
- TOTOLINK T10
- TOTOLINK A3100R
- TOTOLINK A950RG
- TOTOLINK A800R
- TOTOLINK N600R
- TOTOLINK A3000RU
- TOTOLINK A810R
📦 What is this software?
T10 Firmware by Totolink
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete device compromise, creation of persistent backdoors, lateral movement to internal networks, and botnet recruitment.
Likely Case
Remote code execution allowing attackers to modify router settings, intercept network traffic, or use the device as a pivot point for further attacks.
If Mitigated
Limited impact if devices are behind firewalls with strict inbound filtering, though internal attacks remain possible.
🎯 Exploit Status
Exploit code is publicly available on GitHub. The vulnerability requires no authentication and has a straightforward exploitation path.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: https://www.totolink.net/
Restart Required: Yes
Instructions:
1. Check TOTOLINK website for firmware updates. 2. Download appropriate firmware for your model. 3. Access router admin interface. 4. Navigate to firmware update section. 5. Upload and apply new firmware. 6. Reboot router.
🔧 Temporary Workarounds
Disable Cloud Management
allDisable cloud management features to remove the vulnerable endpoint
Network Segmentation
allIsolate affected routers in separate VLANs with strict firewall rules
🧯 If You Can't Patch
- Block inbound access to port 80/443 on WAN interface using firewall rules
- Disable remote administration and cloud features in router settings
🔍 How to Verify
Check if Vulnerable:
Check router firmware version in admin interface. If version is 4.1.8cu.5241_B20210927, device is vulnerable.Check Version:
Check via router web interface or SSH if available: cat /proc/version or check admin panelVerify Fix Applied:
Verify firmware version has changed from 4.1.8cu.5241_B20210927 after update.📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to /cgi-bin/cstecgi.cgi with FileName parameter
- Multiple failed buffer overflow attempts
- Unexpected process execution
Network Indicators:
- Unusual outbound connections from router
- Traffic to known exploit servers
- Port scanning originating from router
SIEM Query:
source="router_logs" AND uri="/cgi-bin/cstecgi.cgi" AND (method="POST" OR params CONTAINS "FileName")