CVE-2024-7463: Totolink CP900 Buffer Overflow Vulnerability

CVE-2024-7463 Overview

CVE-2024-7463 is a buffer overflow vulnerability in the TOTOLINK CP900 router running firmware version 6.3c.566. The flaw resides in the UploadCustomModule function of /cgi-bin/cstecgi.cgi, where the File argument is processed without proper bounds checking [CWE-120]. Attackers can trigger memory corruption remotely by sending crafted input to the affected CGI endpoint. The exploit details have been publicly disclosed, increasing the likelihood of weaponization against exposed devices. According to the disclosure, the vendor was contacted prior to publication but did not respond.

Critical Impact

Remote attackers with low privileges can corrupt memory on affected TOTOLINK CP900 routers, leading to arbitrary code execution or device compromise.

Affected Products

• TOTOLINK CP900 router (hardware)
• TOTOLINK CP900 firmware version 6.3c.566
• Deployments exposing /cgi-bin/cstecgi.cgi to untrusted networks

Discovery Timeline

• 2024-08-05 - CVE-2024-7463 published to NVD
• 2024-08-15 - Last updated in NVD database

Technical Details for CVE-2024-7463

Vulnerability Analysis

The vulnerability exists in the UploadCustomModule function exposed through /cgi-bin/cstecgi.cgi on the TOTOLINK CP900 router. The function accepts a File parameter that is copied into a fixed-size memory buffer without sufficient length validation. When an attacker submits an oversized value for File, the copy operation writes past the buffer boundary and corrupts adjacent stack or heap memory.

The attack requires network reachability to the device management interface and low-privilege access. Successful exploitation can crash the router or, with controlled overflow content, hijack execution flow on the embedded MIPS or ARM processor. Public disclosure of the technique through VulDB and a GitHub proof-of-concept repository increases the risk of automated scanning and exploitation.

Root Cause

The root cause is classic improper restriction of operations within the bounds of a memory buffer [CWE-120]. The CGI handler in cstecgi.cgi does not validate the length of attacker-supplied input before performing a memory copy. Embedded router firmware commonly uses unsafe C string functions such as strcpy or sprintf in HTTP parameter handlers, which is consistent with the described behavior.

Attack Vector

The attack vector is network-based. An attacker sends a crafted HTTP request to /cgi-bin/cstecgi.cgi that invokes the UploadCustomModule action with an overlong File argument. No user interaction is required. While the CVSS vector indicates low privileges are needed, many TOTOLINK deployments use default or weak credentials, lowering the effective bar for exploitation. The vulnerability affects confidentiality, integrity, and availability of the device.

No verified exploit code is republished here. Technical details are documented in the GitHub vulnerability writeup and the VulDB entry #273556.

Detection Methods for CVE-2024-7463

Indicators of Compromise

• HTTP POST requests to /cgi-bin/cstecgi.cgi containing the UploadCustomModule action with abnormally long File parameter values
• Unexpected reboots, watchdog resets, or service crashes on TOTOLINK CP900 devices
• Outbound connections from the router to unfamiliar hosts following suspicious CGI requests

Detection Strategies

• Inspect web server and reverse proxy logs for requests targeting cstecgi.cgi with payloads exceeding expected File parameter lengths
• Deploy network IDS signatures matching oversized parameters in HTTP requests to embedded router management endpoints
• Correlate router crash events with preceding inbound HTTP traffic to the management interface

Monitoring Recommendations

• Forward router syslog and HTTP access logs to a central logging platform for retention and analysis
• Alert on any external (WAN-side) access to the router administrative interface
• Monitor for new firmware modules or configuration changes that were not initiated by an administrator

How to Mitigate CVE-2024-7463

Immediate Actions Required

• Restrict access to the router web management interface to trusted internal networks only and disable WAN-side administration
• Change default credentials on all TOTOLINK CP900 devices and enforce strong, unique passwords
• Place affected routers behind a network segment that blocks untrusted inbound HTTP traffic to /cgi-bin/cstecgi.cgi
• Inventory all TOTOLINK CP900 devices running firmware 6.3c.566 and prioritize replacement or isolation

Patch Information

As of the last NVD update on 2024-08-15, no vendor patch is referenced. The disclosure notes that TOTOLINK was contacted but did not respond. Organizations should monitor the TOTOLINK support site for future firmware updates and consider replacing the device if no fix is released. Refer to VulDB #273556 for tracking updates.

Workarounds

• Block external access to TCP ports hosting the router web interface using upstream firewall rules
• Disable remote management features in the router configuration where supported
• Replace internet-exposed TOTOLINK CP900 units with devices from vendors that maintain an active security response process

# Configuration example: block external access to router management interface
# Replace 192.0.2.10 with the router IP and adjust the WAN interface name
iptables -A FORWARD -i eth_wan -p tcp -d 192.0.2.10 --dport 80 -j DROP
iptables -A FORWARD -i eth_wan -p tcp -d 192.0.2.10 --dport 443 -j DROP