CVE-2026-31179: Totolink A3300r Firmware RCE Vulnerability

CVE-2026-31179 Overview

CVE-2026-31179 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 stunPort parameter is passed to a system shell without proper sanitization. Remote attackers can inject arbitrary operating system commands over the network without authentication. The vulnerability is classified under CWE-77 (Improper Neutralization of Special Elements used in a Command).

Critical Impact
Unauthenticated network attackers can execute arbitrary commands on affected ToToLink A3300R routers, enabling device takeover, traffic interception, and pivoting into internal networks.

Affected Products

ToToLink A3300R router (hardware)
ToToLink A3300R firmware version 17.0.0cu.557_B20221024
Deployments exposing the web management interface (cstecgi.cgi) to untrusted networks

Discovery Timeline

2026-04-23 - CVE-2026-31179 published to NVD
2026-04-27 - Last updated in NVD database

Technical Details for CVE-2026-31179

Vulnerability Analysis

The vulnerability is a command injection flaw in the ToToLink A3300R web management interface. The cstecgi.cgi binary handles configuration requests submitted to /cgi-bin/cstecgi.cgi and processes a stunPort parameter related to STUN (Session Traversal Utilities for NAT) configuration. The parameter value is incorporated into a shell command without input validation or argument quoting.

Attackers reach the endpoint over the network and do not require authentication or user interaction. Successful exploitation yields command execution under the privileges of the web service, which on consumer routers typically runs as root. Impact is limited in scope to the device, but a compromised router provides a foothold for lateral movement and traffic manipulation.

Root Cause

The firmware concatenates the attacker-controlled stunPort value directly into a shell command string before invoking it. Shell metacharacters such as ;, |, &, and backticks are not filtered or escaped, allowing the input to break out of the intended argument context and introduce additional commands.

Attack Vector

An attacker crafts an HTTP request to /cgi-bin/cstecgi.cgi with a malicious stunPort value containing shell metacharacters followed by arbitrary commands. The vulnerable handler invokes the shell with the concatenated string, executing the injected payload. Because the management interface is reachable over the LAN by default, and may be exposed to the WAN through misconfiguration, the attack surface extends beyond local administrators.

A proof-of-concept demonstrating the request structure and the vulnerable parameter handling is available in the Svigo-o TOTOLINK PoC Repository.

Detection Methods for CVE-2026-31179

Indicators of Compromise

HTTP POST requests to /cgi-bin/cstecgi.cgi containing shell metacharacters (;, |, &, `, $() within the stunPort field
Outbound connections from the router to unexpected hosts following management interface requests
Unexpected processes spawned by cstecgi.cgi such as wget, curl, tftp, nc, or shell interpreters

Detection Strategies

Inspect HTTP request bodies destined for cstecgi.cgi and flag non-numeric values in the stunPort parameter
Correlate web request logs with downstream child-process telemetry from the router where available
Hunt for newly created listeners or reverse shells originating from router IP ranges

Monitoring Recommendations

Restrict access to the router management interface to a dedicated administrative VLAN and log all access
Monitor DNS queries originating from router IPs for anomalous lookups indicative of staged payload retrieval
Alert on any WAN-side requests to cstecgi.cgi, which should never occur in normal operation

How to Mitigate CVE-2026-31179

Immediate Actions Required

Disable remote (WAN-side) administration on affected A3300R devices until a vendor patch is available
Restrict LAN access to the management interface to trusted administrative hosts only
Replace end-of-support or unpatched A3300R units in high-risk environments with a maintained alternative

Patch Information

No vendor advisory or fixed firmware version has been published for CVE-2026-31179 at the time of NVD publication. Monitor the ToToLink download portal for firmware updates superseding 17.0.0cu.557_B20221024 and apply them as soon as they are released.

Workarounds

Block external access to TCP ports used by the router HTTP management service at the upstream firewall
Place affected devices behind a network segment that denies inbound traffic to /cgi-bin/cstecgi.cgi from untrusted sources
Use ACLs on the router to restrict the source IP addresses permitted to reach the web interface

bash

# Example upstream ACL to block external access to the router management interface
# Replace ROUTER_WAN_IP with the router's WAN 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