CVE-2025-7615: Totolink T6 Firmware RCE Vulnerability

CVE-2025-7615 Overview

CVE-2025-7615 is a command injection vulnerability affecting the TOTOLINK T6 router running firmware version 4.1.5cu.748. The flaw resides in the clearPairCfg function of the /cgi-bin/cstecgi.cgi endpoint, which serves as an HTTP POST request handler. Attackers can manipulate the ip argument to inject arbitrary operating system commands. The vulnerability is exploitable remotely and requires only low-level privileges. Public disclosure has occurred, and exploit details are accessible through third-party vulnerability databases. The issue is categorized under CWE-74, covering improper neutralization of special elements in downstream components.

Critical Impact
Authenticated remote attackers can execute arbitrary commands on the underlying router operating system by sending crafted POST requests to the affected CGI endpoint.

Affected Products

TOTOLINK T6 router (hardware)
TOTOLINK T6 firmware version 4.1.5cu.748_b20211015
Deployments exposing the /cgi-bin/cstecgi.cgi interface to untrusted networks

Discovery Timeline

2025-07-14 - CVE-2025-7615 published to the National Vulnerability Database
2026-04-29 - Last updated in NVD database

Technical Details for CVE-2025-7615

Vulnerability Analysis

The vulnerability exists in the clearPairCfg function handled by the cstecgi.cgi binary on TOTOLINK T6 devices. This CGI binary processes HTTP POST requests from the administrative web interface and dispatches them to internal handler functions based on the topicurl parameter. The clearPairCfg handler accepts an ip parameter that is passed to a shell execution context without proper sanitization or input validation. Attackers supplying shell metacharacters within the ip argument cause the embedded command interpreter to execute attacker-supplied commands alongside the intended operation. Successful exploitation yields command execution in the context of the web server process, which typically runs with root privileges on consumer-grade routers.

Root Cause

The root cause is improper neutralization of special elements passed to a downstream component [CWE-74]. The clearPairCfg handler concatenates the user-supplied ip value into a system command string without filtering shell metacharacters such as semicolons, backticks, pipes, or command substitution sequences. The firmware lacks both input validation at the request parsing layer and safe command execution APIs.

Attack Vector

Attackers reach the vulnerability over the network by sending an HTTP POST request to /cgi-bin/cstecgi.cgi with a JSON body specifying topicurl=clearPairCfg and a malicious ip field. Exploitation requires low-level authenticated access to the management interface. When the router web interface is exposed to the internet or accessible from an untrusted LAN segment, the attack surface expands accordingly.

No verified proof-of-concept code is reproduced here. Technical exploitation details are documented in the GitHub Vulnerability Document and the VulDB entry #316315.

Detection Methods for CVE-2025-7615

Indicators of Compromise

HTTP POST requests to /cgi-bin/cstecgi.cgi containing the topicurl=clearPairCfg parameter combined with shell metacharacters in the ip field
Unexpected child processes spawned by the router web server (boa, lighttpd, or equivalent) executing shell commands
Outbound connections from the router to unfamiliar hosts following administrative interface access
New or modified files in writable firmware partitions, including persistence scripts in /etc/ or /tmp/

Detection Strategies

Inspect web server access logs on the router for POST requests targeting cstecgi.cgi with anomalous payloads containing ;, |, $(), or backtick characters
Deploy network-based intrusion detection rules that match the URI path /cgi-bin/cstecgi.cgi combined with shell metacharacters in the request body
Correlate router management traffic with source IP addresses outside expected administrative ranges

Monitoring Recommendations

Forward router syslog output to a centralized logging system for retention and analysis
Monitor for configuration changes, firmware modifications, and new administrative sessions on the affected devices
Track DNS queries and outbound traffic from router management VLANs to identify command-and-control activity originating from compromised devices

How to Mitigate CVE-2025-7615

Immediate Actions Required

Restrict access to the router administrative interface to trusted management networks only and disable remote WAN-side administration
Change default and weak administrative credentials, since exploitation requires authenticated access
Segment vulnerable TOTOLINK T6 devices from sensitive internal networks until a firmware update is available
Monitor the TOTOLINK support site for firmware updates addressing this issue

Patch Information

At the time of publication, no vendor patch had been referenced in the NVD entry for CVE-2025-7615. Administrators should consult the TOTOLINK Security Information page for the most current firmware release for the T6 platform and apply updates as they become available.

Workarounds

Place the router behind an upstream firewall that blocks unauthenticated access to TCP ports serving the web management interface
Disable any port forwarding or UPnP rules that expose the management interface to the public internet
Replace end-of-support hardware with actively maintained equipment when vendor patches are not forthcoming

bash

# Example iptables rule to restrict management interface access to a trusted subnet
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP