CVE-2026-5679: Totolink A3300R Command Injection Vulnerability

CVE-2026-5679 Overview

A command injection vulnerability has been identified in the Totolink A3300R router firmware version 17.0.0cu.557_B20221024. The vulnerability exists in the vsetTr069Cfg function within the /cgi-bin/cstecgi.cgi file, where improper handling of the stun_pass argument allows an attacker to inject arbitrary OS commands. This vulnerability has been publicly disclosed and proof-of-concept exploit code is available.

Critical Impact

Successful exploitation allows authenticated attackers on adjacent networks to execute arbitrary system commands on the affected router, potentially leading to complete device compromise, network traffic interception, or lateral movement within the network.

Affected Products

• Totolink A3300R Firmware Version 17.0.0cu.557_B20221024

Discovery Timeline

• 2026-04-06 - CVE-2026-5679 published to NVD
• 2026-04-07 - Last updated in NVD database

Technical Details for CVE-2026-5679

Vulnerability Analysis

This vulnerability is classified as CWE-77 (Improper Neutralization of Special Elements used in a Command). The vsetTr069Cfg function in the Totolink A3300R router's CGI binary fails to properly sanitize user-supplied input in the stun_pass parameter before passing it to system shell commands.

The attack requires adjacent network access and low-privilege authentication, meaning an attacker must have network proximity to the target device and possess valid credentials. While the required access conditions somewhat limit the attack surface, the vulnerability's exploitation is straightforward once those prerequisites are met.

Upon successful exploitation, an attacker can execute arbitrary operating system commands with the privileges of the web server process, typically running as root on embedded devices like routers. This could lead to unauthorized access to sensitive configuration data, modification of DNS settings for traffic interception, installation of persistent backdoors, or using the compromised router as a pivot point for further network attacks.

Root Cause

The root cause is insufficient input validation in the vsetTr069Cfg function. When processing the stun_pass argument, the function directly incorporates user input into shell commands without proper sanitization or escaping of special characters. This allows an attacker to break out of the intended command context and inject additional commands.

Attack Vector

The attack is conducted from an adjacent network, requiring the attacker to be on the same network segment as the vulnerable router. Authentication with low-level privileges is required to access the affected CGI endpoint.

The exploitation flow typically follows this pattern:

1. Attacker authenticates to the router's web interface with valid credentials
2. Attacker crafts a malicious HTTP request to /cgi-bin/cstecgi.cgi targeting the vsetTr069Cfg function
3. The stun_pass parameter contains command injection payloads using shell metacharacters
4. The injected commands execute on the router with elevated privileges

Technical details and proof-of-concept code are available at the GitHub PoC Repository.

Detection Methods for CVE-2026-5679

Indicators of Compromise

• Unusual HTTP POST requests to /cgi-bin/cstecgi.cgi containing shell metacharacters (;, |, $(), backticks) in the stun_pass parameter
• Unexpected outbound connections from the router to external IP addresses
• Modified router configuration files or unexpected processes running on the device
• Anomalous DNS resolution behavior or traffic redirects through the network

Detection Strategies

• Implement network intrusion detection rules to monitor HTTP traffic to router management interfaces for command injection patterns
• Deploy web application firewall (WAF) rules on network segments to detect and block requests containing OS command injection payloads in CGI parameters
• Monitor router syslog output for unusual command executions or error messages related to the TR-069 configuration module

Monitoring Recommendations

• Enable and centralize logging from router management interfaces to a SIEM solution
• Configure alerting for multiple failed authentication attempts followed by successful logins to router admin panels
• Implement network segmentation monitoring to detect lateral movement from compromised IoT devices

How to Mitigate CVE-2026-5679

Immediate Actions Required

• Restrict access to the router's administrative interface to trusted IP addresses only
• Disable remote management features if not required
• Implement strong, unique passwords for all router accounts
• Place management interfaces on isolated VLANs accessible only to authorized administrators

Patch Information

At the time of publication, no official patch has been released by Totolink. Monitor the TOTOLINK Official Website for firmware updates addressing this vulnerability. Additional technical details are available at VulDB #355506.

Workarounds

• Implement access control lists (ACLs) to restrict access to the /cgi-bin/cstecgi.cgi endpoint from untrusted network segments
• Consider deploying a network-level firewall or IPS in front of the affected device to filter malicious requests
• If TR-069 remote management functionality is not required, disable it through the router's configuration interface
• Replace the affected device with a patched or alternative product if the risk is deemed unacceptable

# Example network-level mitigation using iptables on a gateway device
# 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 only from management VLAN
iptables -I FORWARD -s <MGMT_VLAN_SUBNET> -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT
iptables -I FORWARD -s <MGMT_VLAN_SUBNET> -d <ROUTER_IP> -p tcp --dport 443 -j ACCEPT