CVE-2026-1155: Totolink LR350 Buffer Overflow Vulnerability

CVE-2026-1155 Overview

A buffer overflow vulnerability has been discovered in Totolink LR350 firmware version 9.3.5u.6369_B20220309. The vulnerability exists in the setWiFiEasyGuestCfg function within the /cgi-bin/cstecgi.cgi file. An attacker can exploit this vulnerability by manipulating the ssid argument, leading to a buffer overflow condition. The attack can be performed remotely over the network, and a public exploit has been disclosed, increasing the risk of exploitation in the wild.

Critical Impact

Remote attackers with low privileges can exploit this buffer overflow to potentially achieve full compromise of the affected Totolink LR350 router, impacting confidentiality, integrity, and availability of the device and connected network.

Affected Products

• Totolink LR350 firmware version 9.3.5u.6369_B20220309
• Totolink LR350 devices with vulnerable CGI interface
• Network environments utilizing affected Totolink routers

Discovery Timeline

• 2026-01-19 - CVE CVE-2026-1155 published to NVD
• 2026-01-19 - Last updated in NVD database

Technical Details for CVE-2026-1155

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The setWiFiEasyGuestCfg function in the Totolink LR350's CGI handler fails to properly validate the length of user-supplied input for the ssid parameter before copying it into a fixed-size memory buffer. When an attacker provides an oversized ssid value, the function writes beyond the allocated buffer boundary, corrupting adjacent memory regions.

The network-accessible nature of the vulnerability via the /cgi-bin/cstecgi.cgi endpoint makes it particularly dangerous, as attackers can target these devices remotely without physical access. While authentication may be required (low privileges), compromised or weak credentials are common in consumer router deployments.

Root Cause

The root cause is improper input validation in the setWiFiEasyGuestCfg function. The code does not enforce boundary checks on the ssid argument before performing memory operations. This allows an attacker to supply a maliciously crafted ssid string that exceeds the expected buffer size, resulting in memory corruption. Embedded devices like routers often lack modern memory protection mechanisms such as ASLR or stack canaries, making buffer overflow exploitation more reliable.

Attack Vector

The attack is performed remotely over the network by sending a specially crafted HTTP request to the /cgi-bin/cstecgi.cgi endpoint with an oversized ssid parameter value in the setWiFiEasyGuestCfg function call. The attacker must have low-level authenticated access to the router's web interface, though default or weak credentials are commonly found on IoT devices like the Totolink LR350.

The exploitation process involves:

1. Identifying a vulnerable Totolink LR350 device on the network
2. Authenticating to the web interface (or exploiting weak default credentials)
3. Sending a malicious request to /cgi-bin/cstecgi.cgi with an oversized ssid parameter
4. The buffer overflow corrupts memory, potentially allowing code execution or denial of service

Technical details regarding the specific exploitation methodology can be found in the vulnerability disclosure documentation and VulDB entry #341749.

Detection Methods for CVE-2026-1155

Indicators of Compromise

• Unusual HTTP POST requests to /cgi-bin/cstecgi.cgi containing abnormally long ssid parameter values
• Router crashes, reboots, or unresponsive web interface indicating potential exploitation attempts
• Unexpected changes to router configuration, particularly WiFi guest network settings
• Network traffic anomalies originating from the router to unknown external hosts

Detection Strategies

• Implement network monitoring rules to detect HTTP requests to /cgi-bin/cstecgi.cgi with ssid parameters exceeding normal length thresholds (typically 32 characters for SSIDs)
• Deploy intrusion detection signatures that identify buffer overflow patterns targeting Totolink devices
• Monitor router logs for repeated authentication attempts followed by configuration change requests
• Use network-based vulnerability scanners to identify exposed Totolink LR350 devices with vulnerable firmware versions

Monitoring Recommendations

• Enable logging on network perimeter devices to capture traffic to and from IoT devices like routers
• Implement alerting for any configuration changes to router guest WiFi settings outside of maintenance windows
• Monitor for unexpected outbound connections from router management interfaces
• Regularly audit device firmware versions across the network to identify vulnerable Totolink installations

How to Mitigate CVE-2026-1155

Immediate Actions Required

• Isolate affected Totolink LR350 devices from untrusted network segments immediately
• Restrict access to the router's web management interface to trusted internal networks only
• Change default credentials and implement strong, unique passwords for router administration
• Disable remote management features if not required for operations
• Monitor for firmware updates from Totolink and apply patches as soon as available

Patch Information

At the time of publication, no official patch has been confirmed from Totolink for this vulnerability. Organizations should monitor the TOTOLINK Official Website for security updates and firmware releases addressing CVE-2026-1155. Additional tracking information is available at VulDB #341749.

Workarounds

• Implement network-level access controls (ACLs) to restrict access to the CGI interface from untrusted sources
• Deploy a Web Application Firewall (WAF) or network IPS rule to block requests with oversized ssid parameters to /cgi-bin/cstecgi.cgi
• Consider replacing vulnerable devices with alternative router hardware if patching is not available
• Segment IoT devices including routers onto isolated network VLANs with restricted internet access

# Example iptables rule to restrict access to router management interface
# Apply on a network firewall or gateway device
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 trusted management subnet
iptables -I FORWARD -s <TRUSTED_MGMT_SUBNET> -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT
iptables -I FORWARD -s <TRUSTED_MGMT_SUBNET> -d <ROUTER_IP> -p tcp --dport 443 -j ACCEPT