CVE-2026-5977: Totolink A7100RU RCE Vulnerability

CVE-2026-5977 Overview

A critical OS command injection vulnerability has been identified in the Totolink A7100RU router firmware version 7.4cu.2313_b20191024. This vulnerability affects the setWiFiBasicCfg function within the /cgi-bin/cstecgi.cgi CGI Handler component. By manipulating the wifiOff argument, an attacker can inject and execute arbitrary operating system commands on the affected device. The vulnerability is remotely exploitable without authentication, making it particularly dangerous for internet-exposed devices.

Critical Impact

Remote attackers can execute arbitrary system commands on affected Totolink A7100RU routers through command injection in the WiFi configuration handler, potentially leading to complete device compromise, network infiltration, and use as a pivot point for further attacks.

Affected Products

• Totolink A7100RU firmware version 7.4cu.2313_b20191024
• CGI Handler component (/cgi-bin/cstecgi.cgi)
• setWiFiBasicCfg function

Discovery Timeline

• April 9, 2026 - CVE-2026-5977 published to NVD
• April 9, 2026 - Last updated in NVD database

Technical Details for CVE-2026-5977

Vulnerability Analysis

This command injection vulnerability (CWE-77) exists in the Totolink A7100RU router's web management interface. The setWiFiBasicCfg function, responsible for handling WiFi configuration changes, fails to properly sanitize the wifiOff parameter before passing it to system shell commands. When a user submits WiFi configuration data through the CGI handler, the router processes the request without adequate input validation, allowing shell metacharacters and command sequences to be interpreted by the underlying operating system.

The vulnerability is particularly severe because it requires no prior authentication, can be exploited remotely over the network, and provides direct command execution at the system level. An exploit for this vulnerability has been made publicly available, increasing the risk of active exploitation in the wild.

Root Cause

The root cause of this vulnerability is insufficient input validation and improper neutralization of special elements used in OS commands. The setWiFiBasicCfg function directly incorporates user-supplied data from the wifiOff parameter into shell command construction without proper sanitization or escaping. This allows attackers to break out of the intended command context and execute arbitrary commands using shell metacharacters such as semicolons, pipes, backticks, or command substitution syntax.

Attack Vector

The attack can be executed remotely over the network by sending a specially crafted HTTP request to the /cgi-bin/cstecgi.cgi endpoint. An attacker would target the setWiFiBasicCfg function and inject malicious commands through the wifiOff parameter. The injected commands execute with the privileges of the web server process, which typically runs as root on embedded devices like this router. This can lead to complete system compromise, including extraction of credentials, modification of device configuration, installation of persistent backdoors, or use of the device in botnet attacks.

The vulnerability can be exploited by crafting a malicious HTTP POST request that includes command injection payloads in the wifiOff parameter value. Common techniques include using command separators like ;, |, or && followed by arbitrary commands, or utilizing command substitution syntax such as backticks or $() to embed malicious commands.

Detection Methods for CVE-2026-5977

Indicators of Compromise

• Unusual outbound connections from the router to unknown external IP addresses
• Unexpected processes running on the router device
• Modified configuration files or unauthorized administrative accounts
• HTTP access logs showing suspicious requests to /cgi-bin/cstecgi.cgi with unusual wifiOff parameter values
• Network traffic indicating command-and-control communication from the router

Detection Strategies

• Monitor HTTP traffic to the router's management interface for requests containing shell metacharacters (;, |, &, backticks, $()) in parameter values
• Implement network-based intrusion detection rules to identify command injection attempts targeting CGI endpoints
• Review router access logs for POST requests to /cgi-bin/cstecgi.cgi with the setWiFiBasicCfg function
• Deploy endpoint detection on network segments to identify lateral movement originating from compromised router IP addresses

Monitoring Recommendations

• Enable comprehensive logging on the Totolink router if supported by the firmware
• Implement network segmentation to isolate IoT and router management interfaces from critical network assets
• Monitor for DNS queries or connections to known malicious infrastructure from the router's IP address
• Regularly audit router configurations for unauthorized changes or additional user accounts

How to Mitigate CVE-2026-5977

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses only
• Disable remote management access from the WAN/Internet interface immediately
• Place the router behind a firewall that filters malicious requests to CGI endpoints
• Consider replacing the affected device with a router from a vendor with better security update practices
• Monitor for any firmware updates from Totolink that address this vulnerability

Patch Information

At the time of publication, no official patch information has been released by Totolink for this vulnerability. Users should monitor the Totolink official website for security advisories and firmware updates. Additional technical details about this vulnerability can be found in the GitHub vulnerability repository and VulDB entry #356531.

Workarounds

• Disable the web management interface entirely if not required for daily operations
• Implement firewall rules to block external access to port 80/443 on the router's WAN interface
• Use a separate, more secure router or firewall appliance in front of the affected device
• Configure access control lists (ACLs) to permit management access only from specific trusted IP addresses
• Consider network segmentation to limit the blast radius if the device is compromised

# Example firewall rule to restrict management access (implement on upstream firewall)
# Block external access to router management interface
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -j DROP

# Allow management only from trusted admin workstation
iptables -I FORWARD -s <trusted_admin_ip> -d <router_ip> -p tcp --dport 80 -j ACCEPT