CVE-2026-31175: Totolink A3300R Firmware RCE Vulnerability

CVE-2026-31175 Overview

CVE-2026-31175 is a command injection vulnerability in ToToLink A3300R firmware version 17.0.0cu.557_B20221024. The flaw resides in the /cgi-bin/cstecgi.cgi endpoint, where the stunEnable parameter is passed to a system shell without proper sanitization. Unauthenticated remote attackers can inject arbitrary operating system commands by crafting malicious HTTP requests targeting this parameter. Successful exploitation grants attackers code execution on the underlying router, typically with elevated privileges. The vulnerability is tracked under CWE-77: Improper Neutralization of Special Elements used in a Command.

Critical Impact
Unauthenticated attackers can execute arbitrary commands on affected ToToLink A3300R routers over the network, leading to complete device compromise.

Affected Products

ToToLink A3300R router hardware
ToToLink A3300R firmware version 17.0.0cu.557_B20221024
Deployments exposing the router web interface to untrusted networks

Discovery Timeline

2026-04-23 - CVE-2026-31175 published to the National Vulnerability Database (NVD)
2026-04-24 - Last updated in NVD database

Technical Details for CVE-2026-31175

Vulnerability Analysis

The vulnerability exists in the cstecgi.cgi binary, which handles configuration requests on the ToToLink A3300R web management interface. When a request is sent to /cgi-bin/cstecgi.cgi containing the stunEnable parameter, the value is concatenated into a shell command string and executed without input validation or escaping. Attackers can break out of the intended command context using shell metacharacters such as ;, |, and backticks. The injected commands run in the context of the CGI process, which on consumer router firmware typically runs as root. This produces full administrative control over the device.

Root Cause

The root cause is improper neutralization of special elements in a shell command [CWE-77]. The CGI handler trusts attacker-controlled values from HTTP request parameters and passes them directly to a system() style call. There is no allow-list of expected values for stunEnable, no escaping of shell metacharacters, and no authentication boundary preventing remote callers from reaching the vulnerable handler.

Attack Vector

Exploitation requires only network access to the router web interface. An attacker sends a single HTTP POST request to /cgi-bin/cstecgi.cgi with a stunEnable value containing injected shell syntax. No credentials, user interaction, or prior foothold are required. Where the management interface is exposed to the WAN, the attack is fully internet-reachable. Successful exploitation enables persistence, traffic interception, lateral movement into the LAN, recruitment into botnets, and DNS hijacking.

A proof-of-concept demonstrating the request structure is published in the TOTOLINK-Vul GitHub repository.

Detection Methods for CVE-2026-31175

Indicators of Compromise

HTTP requests to /cgi-bin/cstecgi.cgi containing shell metacharacters (;, |, &, `, $()) inside the stunEnable parameter
Unexpected outbound connections from the router to attacker infrastructure following web requests
New or modified processes spawned from the cstecgi.cgi parent on the device
Configuration changes to DNS servers, firewall rules, or remote management settings without administrator action

Detection Strategies

Inspect web server and reverse proxy logs in front of router management interfaces for POST bodies containing stunEnable= followed by non-boolean values
Deploy network intrusion detection signatures that flag command injection payloads against cstecgi.cgi
Monitor egress traffic from network devices for anomalous protocols, tunneling, or connections to known malicious IPs

Monitoring Recommendations

Forward router syslog and management plane logs to a centralized SIEM for correlation against IOC feeds
Alert on any HTTP traffic to router administrative paths originating from untrusted network segments
Track firmware versions across the fleet to identify devices running 17.0.0cu.557_B20221024

How to Mitigate CVE-2026-31175

Immediate Actions Required

Disable remote (WAN-side) administration on affected ToToLink A3300R devices immediately
Restrict access to the LAN-side management interface to a dedicated administrative VLAN or host
Audit existing devices for unauthorized configuration changes, new accounts, and unexpected processes
Rotate credentials and pre-shared keys on any device suspected of compromise

Patch Information

At the time of publication, no vendor advisory or fixed firmware release is referenced in the CVE record. Administrators should monitor the ToToLink support site for an updated firmware build that supersedes 17.0.0cu.557_B20221024 and apply it once released. Until a patch is published, treat affected devices as compromised if exposed to untrusted networks.

Workarounds

Block inbound access to TCP ports 80 and 443 on the router WAN interface using upstream filtering
Place the router behind a separate firewall that denies untrusted traffic to its management plane
Replace affected devices in high-risk environments with hardware that has a current security support lifecycle

bash

# Example upstream ACL to block WAN access to the router management interface
# Apply on the upstream firewall, replacing ROUTER_WAN_IP with the device address
iptables -I FORWARD -d ROUTER_WAN_IP -p tcp --dport 80  -j DROP
iptables -I FORWARD -d ROUTER_WAN_IP -p tcp --dport 443 -j DROP
iptables -I FORWARD -d ROUTER_WAN_IP -p tcp --dport 8080 -j DROP