CVE-2024-7157: Totolink A3100r Buffer Overflow Vulnerability

CVE-2024-7157 Overview

CVE-2024-7157 is a buffer overflow vulnerability in the TOTOLINK A3100R router running firmware version 4.1.2cu.5050_B20200504. The flaw resides in the getSaveConfig function accessed via /cgi-bin/cstecgi.cgi?action=save&setting. An attacker can manipulate the http_host argument to trigger a buffer overflow condition [CWE-120]. The vulnerability is remotely exploitable and has been publicly disclosed with exploit details available. The vendor was contacted about this disclosure but did not respond.

Critical Impact
Remote attackers with low privileges can exploit the buffer overflow to compromise confidentiality, integrity, and availability of the affected router.

Affected Products

TOTOLINK A3100R router (hardware)
TOTOLINK A3100R firmware version 4.1.2cu.5050_B20200504
Devices exposing the cstecgi.cgi web interface

Discovery Timeline

2024-07-28 - CVE-2024-7157 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2024-7157

Vulnerability Analysis

The vulnerability affects the getSaveConfig function within the CGI handler /cgi-bin/cstecgi.cgi on the TOTOLINK A3100R router. When processing requests with action=save&setting, the function copies the user-supplied http_host parameter into a fixed-size stack buffer without validating input length. Attackers can send an oversized http_host value to overflow the buffer and corrupt adjacent memory regions.

Because the CGI process runs with elevated privileges on the embedded device, successful exploitation can lead to arbitrary code execution or full device compromise. The exploit prediction score of 7.37% places this vulnerability in the 93rd percentile of likely-to-be-exploited issues, reflecting active interest in TOTOLINK devices among botnet operators.

Root Cause

The root cause is a classic buffer overflow ([CWE-120]) caused by an unbounded copy operation. The getSaveConfig handler does not enforce length limits on the http_host argument before writing it to a stack-allocated buffer. This category of flaw is common in MIPS-based embedded routers where developers use unsafe C string functions such as strcpy or sprintf without size checks.

Attack Vector

Exploitation requires network access to the router's web management interface and low-privilege authenticated access. An attacker sends a crafted HTTP request to /cgi-bin/cstecgi.cgi?action=save&setting containing an oversized http_host parameter. The overflow overwrites the return address on the stack, allowing control of program execution. Public exploit documentation exists in the IoT-vulnerable repository, lowering the barrier for weaponization.

The vulnerability manifests in the request handling logic of the CGI binary. See the VulDB entry #272571 for additional technical context.

Detection Methods for CVE-2024-7157

Indicators of Compromise

HTTP POST or GET requests to /cgi-bin/cstecgi.cgi?action=save&setting containing abnormally long http_host values
Router process crashes, reboots, or watchdog resets following external web requests
Outbound connections from the router to unknown command and control infrastructure
New or modified firmware configuration entries that were not made by administrators

Detection Strategies

Inspect network traffic to router management interfaces for oversized parameters in cstecgi.cgi requests
Deploy IDS signatures that flag http_host parameter lengths exceeding typical hostname boundaries (255 bytes)
Correlate router availability logs with inbound HTTP requests to identify crash-triggering payloads
Monitor DNS and outbound traffic from router IP addresses for anomalous destinations

Monitoring Recommendations

Restrict access to router administration interfaces and log all authentication attempts
Baseline expected CGI parameter sizes and alert on statistical outliers
Enable syslog forwarding from routers to a centralized logging platform for correlation

How to Mitigate CVE-2024-7157

Immediate Actions Required

Disable remote management on the WAN interface of the TOTOLINK A3100R
Restrict LAN access to the administration interface using ACLs or management VLANs
Rotate administrative credentials to reduce the risk of low-privilege exploitation chains
Segment vulnerable routers away from sensitive internal networks until a patch is available

Patch Information

No vendor patch is currently available. TOTOLINK did not respond to the coordinated disclosure attempt referenced in the VulDB submission. Organizations should treat affected devices as unpatchable and plan replacement with a supported product.

Workarounds

Place the router behind an upstream firewall that blocks unsolicited inbound HTTP and HTTPS traffic
Use a web application firewall or reverse proxy to filter requests to cstecgi.cgi and drop oversized http_host values
Replace end-of-support TOTOLINK A3100R hardware with an actively maintained router
Isolate the device on a dedicated network segment with strict egress filtering

bash

# Example iptables rule to block external access to the router admin interface
iptables -A INPUT -p tcp --dport 80 -i wan0 -j DROP
iptables -A INPUT -p tcp --dport 443 -i wan0 -j DROP