CVE-2026-1157: Totolink LR350 Buffer Overflow Vulnerability

CVE-2026-1157 Overview

CVE-2026-1157 is a buffer overflow vulnerability in the Totolink LR350 router running firmware version 9.3.5u.6369_B20220309. The flaw resides in the setWiFiEasyCfg function within /cgi-bin/cstecgi.cgi. Attackers can trigger the condition by manipulating the ssid argument, leading to memory corruption in the embedded web management interface. The vulnerability is exploitable remotely over the network and a public exploit description has been disclosed. The weakness is classified under [CWE-119], improper restriction of operations within the bounds of a memory buffer.

Critical Impact

Remote attackers with low-privilege access can corrupt memory through the ssid parameter, potentially achieving arbitrary code execution on affected Totolink LR350 routers.

Affected Products

• Totolink LR350 router hardware
• Totolink LR350 firmware version 9.3.5u.6369_B20220309
• Deployments exposing the /cgi-bin/cstecgi.cgi management endpoint

Discovery Timeline

• 2026-01-19 - CVE-2026-1157 published to NVD
• 2026-01-29 - Last updated in NVD database

Technical Details for CVE-2026-1157

Vulnerability Analysis

The vulnerability exists in the setWiFiEasyCfg handler exposed through the Common Gateway Interface (CGI) binary cstecgi.cgi. This handler accepts an ssid argument from HTTP requests and copies it into a fixed-size buffer without enforcing length validation. When the supplied ssid value exceeds the destination buffer size, adjacent memory is overwritten.

On embedded MIPS/ARM devices like the LR350, such buffer overflows often allow attackers to overwrite saved return addresses or function pointers. The result is denial of service at minimum and arbitrary code execution at worst. The attack requires authenticated access to the management interface, consistent with the low-privilege requirement noted in the CVSS vector.

Public technical details have been documented in the Notion configuration guide and tracked in VulDB entry #341751.

Root Cause

The root cause is the absence of bounds checking when handling the ssid request parameter inside setWiFiEasyCfg. The function performs an unsafe string copy operation into a stack-based or statically sized buffer. This pattern aligns with [CWE-119] and is common across the TOTOLINK cstecgi.cgi family of handlers.

Attack Vector

The attack vector is network-based. An attacker sends a crafted HTTP POST request to /cgi-bin/cstecgi.cgi targeting the setWiFiEasyCfg action with an oversized ssid value. Because the CGI binary is reachable over the LAN and, in misconfigured deployments, over the WAN, exposure increases significantly when remote management is enabled.

The vulnerability manifests when the oversized argument is processed by the unsafe string handling routine inside the CGI binary. See the VulDB CTI record for additional technical context.

Detection Methods for CVE-2026-1157

Indicators of Compromise

• HTTP POST requests to /cgi-bin/cstecgi.cgi containing the setWiFiEasyCfg action with abnormally long ssid parameter values
• Unexpected reboots, crashes, or service restarts of the router web management daemon
• Outbound connections from the router to unfamiliar hosts following management interface access

Detection Strategies

• Inspect web server and CGI access logs for requests targeting setWiFiEasyCfg with ssid payloads exceeding typical SSID length limits (32 bytes)
• Deploy network intrusion detection signatures that flag oversized parameter values in requests to cstecgi.cgi
• Monitor router syslog output for segmentation faults or cstecgi.cgi process termination events

Monitoring Recommendations

• Restrict and audit access to the router management interface from non-administrative network segments
• Forward router logs to a centralized logging platform for long-term retention and correlation
• Track firmware version inventory across deployed LR350 devices to identify vulnerable units

How to Mitigate CVE-2026-1157

Immediate Actions Required

• Disable remote WAN-side management on all Totolink LR350 devices to reduce the attack surface
• Restrict administrative interface access to trusted management VLANs or specific IP allowlists
• Rotate administrator credentials, since exploitation requires low-privileged authentication
• Audit existing devices for firmware version 9.3.5u.6369_B20220309 and prioritize replacement or isolation

Patch Information

At the time of publication, no vendor-supplied patch has been linked in the NVD record. Administrators should monitor the TOTOLINK official site for firmware updates addressing the setWiFiEasyCfg handler. Until a fix is released, compensating controls are required.

Workarounds

• Place affected LR350 devices behind a network segmentation boundary that blocks direct access to /cgi-bin/cstecgi.cgi from untrusted networks
• Use a reverse proxy or firewall rule to drop HTTP requests where the ssid parameter exceeds 32 bytes
• Replace end-of-life or unpatched LR350 hardware with a currently supported router platform

# Example iptables rule to restrict management interface access to a trusted subnet
iptables -A INPUT -p tcp --dport 80 -s 192.168.10.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.10.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP