CVE-2024-7187: Totolink A3600R Buffer Overflow Vulnerability

CVE-2024-7187 Overview

CVE-2024-7187 is a buffer overflow vulnerability in the TOTOLINK A3600R router running firmware version 4.1.2cu.5182_B20201102. The flaw resides in the UploadCustomModule function within /cgi-bin/cstecgi.cgi. Attackers can trigger the overflow by manipulating the File argument, and the attack can be initiated remotely over the network. The exploit has been publicly disclosed, increasing the likelihood of opportunistic exploitation against exposed devices. According to the VulDB submission, the vendor was contacted but did not respond to the disclosure, leaving affected devices without a coordinated fix.

Critical Impact
Remote attackers with low-privilege access can overflow a buffer in the router's CGI handler, potentially achieving arbitrary code execution on the device.

Affected Products

TOTOLINK A3600R router hardware
TOTOLINK A3600R firmware version 4.1.2cu.5182_B20201102
Deployments exposing the /cgi-bin/cstecgi.cgi endpoint to untrusted networks

Discovery Timeline

2024-07-29 - CVE-2024-7187 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2024-7187

Vulnerability Analysis

The vulnerability is a classic buffer overflow classified under [CWE-120], improper restriction of operations within the bounds of a memory buffer. The UploadCustomModule function in /cgi-bin/cstecgi.cgi copies attacker-controlled input from the File parameter into a fixed-size buffer without validating its length. Overwriting adjacent stack memory can corrupt saved return addresses and control flow structures on MIPS-based embedded devices like the A3600R. Successful exploitation may lead to arbitrary code execution in the context of the CGI process, which typically runs with elevated privileges on consumer routers.

Root Cause

The root cause is the absence of bounds checking on the File argument passed to UploadCustomModule. The handler copies user input into a stack buffer using an unsafe string operation, allowing input longer than the buffer to corrupt neighboring memory. Embedded Linux binaries on this platform frequently lack modern mitigations such as stack canaries, address space layout randomization (ASLR), and non-executable stacks, which amplifies exploitability.

Attack Vector

An attacker sends a crafted HTTP request to /cgi-bin/cstecgi.cgi invoking the UploadCustomModule action with an oversized File parameter. The request originates over the network, and the CVSS vector indicates low-privilege authentication is required. Devices exposing the management interface to the WAN or to untrusted LAN segments are directly reachable. Refer to the GitHub IoT Vulnerability Documentation for the disclosed request structure.

No verified proof-of-concept code has been reproduced here. Consult the VulDB Entry #272608 for additional technical context.

Detection Methods for CVE-2024-7187

Indicators of Compromise

HTTP POST requests to /cgi-bin/cstecgi.cgi containing the UploadCustomModule action with unusually large File parameter values.
Unexpected crashes or restarts of the cstecgi.cgi process visible in router system logs.
Outbound connections from the router to unfamiliar hosts, which can indicate post-exploitation staging.

Detection Strategies

Deploy network intrusion detection signatures that inspect HTTP requests to cstecgi.cgi and flag File parameters exceeding expected length thresholds.
Baseline normal administrative traffic to the router and alert on anomalous CGI invocations originating from non-management subnets.
Correlate router log anomalies with perimeter firewall telemetry to identify remote exploitation attempts.

Monitoring Recommendations

Forward router syslog output to a central logging platform and retain HTTP access logs for the management interface.
Monitor egress traffic from router management IPs for connections to internet destinations that are inconsistent with normal firmware update or telemetry behavior.
Track EPSS scoring for CVE-2024-7187 to prioritize response as exploitation likelihood shifts over time.

How to Mitigate CVE-2024-7187

Immediate Actions Required

Restrict access to the router management interface to trusted LAN hosts only and disable remote (WAN-side) administration.
Segment TOTOLINK A3600R devices onto isolated network zones with strict ACLs governing inbound traffic to /cgi-bin/.
Rotate router administrative credentials, since the CVSS vector indicates the attack requires low-privilege authentication that could be brute forced or reused.
Inventory environments for the affected firmware build 4.1.2cu.5182_B20201102 and plan replacement or decommissioning.

Patch Information

At the time of publication, no vendor advisory or patched firmware is listed in the referenced sources. The VulDB submission notes that TOTOLINK did not respond to disclosure attempts. Organizations should treat the device as unpatched and consider replacing it with hardware that receives active security maintenance. Track the VulDB CTI ID #272608 entry for updates.

Workarounds

Block external access to TCP ports serving the router's web administration interface at the perimeter firewall.
Place the affected router behind an upstream firewall or gateway that filters HTTP requests to cstecgi.cgi containing oversized parameters.
Where feasible, replace the TOTOLINK A3600R with a supported device from a vendor providing security updates.

bash

# Example: block WAN access to router HTTP admin interface on an upstream firewall
iptables -I FORWARD -p tcp -d <router-ip> --dport 80 -m state --state NEW -j DROP
iptables -I FORWARD -p tcp -d <router-ip> --dport 443 -m state --state NEW -j DROP

# Restrict LAN admin access to a management subnet only
iptables -I FORWARD -p tcp -d <router-ip> --dport 80 ! -s 10.0.10.0/24 -j DROP