CVE-2026-1157: Totolink LR350 Buffer Overflow Vulnerability

CVE-2026-1157 Overview

A buffer overflow vulnerability has been identified in the TOTOLINK LR350 router running firmware version 9.3.5u.6369_B20220309. This vulnerability affects the setWiFiEasyCfg function within the /cgi-bin/cstecgi.cgi file, where improper handling of the ssid argument enables an attacker to trigger a buffer overflow condition. The vulnerability can be exploited remotely, and exploit information has been made publicly available.

Critical Impact

Remote attackers can exploit this buffer overflow vulnerability to potentially execute arbitrary code or cause denial of service on affected TOTOLINK LR350 devices, compromising network infrastructure security.

Affected Products

• TOTOLINK LR350 Firmware version 9.3.5u.6369_B20220309
• TOTOLINK LR350 devices with vulnerable CGI configuration

Discovery Timeline

• 2026-01-19 - CVE-2026-1157 published to NVD
• 2026-01-19 - Last updated in NVD database

Technical Details for CVE-2026-1157

Vulnerability Analysis

This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw exists in the setWiFiEasyCfg function, which is responsible for handling WiFi Easy Configuration settings on the device. When processing the ssid parameter through the /cgi-bin/cstecgi.cgi endpoint, the function fails to properly validate the length and boundaries of the input data before copying it into a fixed-size memory buffer.

This insufficient boundary checking allows an attacker to supply an overly long ssid value that exceeds the allocated buffer space, resulting in adjacent memory being overwritten. Depending on the memory layout and the attacker's control over the overflow data, this could lead to arbitrary code execution, denial of service through memory corruption, or complete device compromise.

Root Cause

The root cause of this vulnerability lies in the absence of proper input validation and bounds checking within the setWiFiEasyCfg function. The ssid argument is processed without verifying that its length falls within acceptable limits for the destination buffer. This is a classic buffer overflow pattern commonly found in embedded systems and IoT devices where memory-safe programming practices may not be consistently applied.

The vulnerable code path accepts user-supplied data via the CGI interface without sanitization, directly copying the input into a stack or heap buffer of insufficient size. This lack of defensive programming allows attackers to control memory regions beyond the intended buffer boundaries.

Attack Vector

The attack can be executed remotely over the network. An authenticated attacker with low-privilege access can target the /cgi-bin/cstecgi.cgi endpoint and send a malicious HTTP request containing an oversized ssid parameter to the setWiFiEasyCfg function. The attack requires no user interaction and can be automated.

Attackers would typically craft an HTTP POST request to the vulnerable endpoint with a carefully constructed payload in the ssid field. The payload would include enough data to overflow the target buffer, followed by attacker-controlled values designed to hijack program execution flow or corrupt critical data structures.

For detailed technical information about this vulnerability, refer to the Notion Resource on TOTOLINK or the VulDB Report #341751.

Detection Methods for CVE-2026-1157

Indicators of Compromise

• Unusual or malformed HTTP requests targeting /cgi-bin/cstecgi.cgi with abnormally long ssid parameters
• Device crashes, unexpected reboots, or unresponsive web interface indicating potential exploitation attempts
• Network traffic containing encoded or binary payloads directed at TOTOLINK router management interfaces
• Log entries showing repeated failed authentication or configuration change attempts

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests to /cgi-bin/cstecgi.cgi containing ssid parameters exceeding normal length (typically > 32 characters for SSIDs)
• Monitor for anomalous traffic patterns targeting TOTOLINK device management ports
• Deploy SentinelOne Singularity to detect exploitation attempts and memory corruption indicators on protected network segments
• Create alerts for any unexpected process behavior or memory violations on network devices

Monitoring Recommendations

• Enable verbose logging on TOTOLINK devices if available and forward logs to a centralized SIEM solution
• Implement network segmentation to isolate IoT and network infrastructure devices from general network traffic
• Regularly audit network traffic to and from router management interfaces for suspicious activity
• Monitor device health metrics for signs of resource exhaustion or unexpected behavior indicative of exploitation

How to Mitigate CVE-2026-1157

Immediate Actions Required

• Restrict network access to the router's management interface to trusted IP addresses only
• Disable remote management capabilities if not required for operations
• Implement firewall rules to block external access to /cgi-bin/cstecgi.cgi and other CGI endpoints
• Consider isolating affected TOTOLINK LR350 devices on a separate network segment until patched

Patch Information

As of the publication date, no official patch has been confirmed from TOTOLINK. Administrators should monitor the TOTOlink Official Website for firmware updates that address this vulnerability. Until a patch is available, implementing the recommended workarounds is critical to reduce exposure risk.

Check the VulDB #341751 entry for updates on patch availability and additional remediation guidance.

Workarounds

• Implement access control lists (ACLs) to restrict management interface access to authorized IP addresses only
• Use a VPN for remote administration rather than exposing the management interface directly to the network
• Configure upstream firewall rules to filter requests containing oversized parameters targeting the vulnerable endpoint
• If possible, disable the WiFi Easy Configuration feature if not actively used

# Example firewall rule to restrict access to router management (iptables)
# Replace 192.168.1.1 with your router's IP and 192.168.1.100 with trusted admin IP

iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -s 192.168.1.100 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT