CVE-2024-0576: Totolink LR1200GB Buffer Overflow Flaw

CVE-2024-0576 Overview

A critical stack-based buffer overflow vulnerability has been identified in Totolink LR1200GB firmware version 9.1.0u.6619_B20230130. This vulnerability exists within the setIpPortFilterRules function located in the /cgi-bin/cstecgi.cgi file. Improper handling of the sPort argument allows remote attackers to exploit this flaw and potentially achieve complete system compromise without authentication.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to execute arbitrary code on vulnerable Totolink LR1200GB routers, potentially gaining full control of the device and enabling further network intrusion.

Affected Products

• Totolink LR1200GB Firmware version 9.1.0u.6619_B20230130
• Totolink LR1200GB hardware devices

Discovery Timeline

• 2024-01-16 - CVE-2024-0576 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-0576

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), a memory corruption flaw that occurs when user-supplied input exceeds the allocated buffer space on the program stack. The setIpPortFilterRules function in the Totolink LR1200GB router's CGI interface fails to properly validate the length of the sPort parameter before copying it into a fixed-size stack buffer.

Stack-based buffer overflows are particularly dangerous in embedded devices like routers because they often lack modern memory protection mechanisms such as ASLR (Address Space Layout Randomization) or stack canaries. This allows attackers to reliably overwrite the return address on the stack and redirect program execution to attacker-controlled code.

The vulnerability is remotely exploitable without requiring authentication, making it a significant threat to any network where the affected device's management interface is accessible.

Root Cause

The root cause of this vulnerability lies in insufficient input validation within the setIpPortFilterRules function. When processing HTTP requests to /cgi-bin/cstecgi.cgi, the function accepts the sPort parameter without verifying that its length does not exceed the size of the destination buffer. This allows an attacker to supply an overly long string that overwrites adjacent stack memory, including saved return addresses and potentially other critical data structures.

Attack Vector

The attack can be initiated remotely over the network by sending a specially crafted HTTP request to the vulnerable CGI endpoint. An attacker would target the /cgi-bin/cstecgi.cgi interface with a malicious sPort parameter containing a payload designed to overflow the stack buffer. The attack does not require authentication, and successful exploitation could lead to arbitrary code execution with the privileges of the web server process, which typically runs as root on embedded devices.

The exploit has been publicly disclosed, as documented in the GitHub Exploit Documentation. This increases the risk of widespread exploitation against unpatched devices.

Detection Methods for CVE-2024-0576

Indicators of Compromise

• Unusual HTTP POST requests to /cgi-bin/cstecgi.cgi containing abnormally long sPort parameter values
• Unexpected process crashes or restarts of the HTTP daemon on Totolink devices
• Anomalous outbound network connections from the router to unknown external IP addresses
• Presence of unauthorized files or modified firmware on the device

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests to /cgi-bin/cstecgi.cgi with oversized parameter values
• Monitor for buffer overflow attack signatures targeting the setIpPortFilterRules function
• Deploy deep packet inspection to analyze CGI requests for malformed or oversized input parameters
• Review router logs for repeated failed authentication attempts or unusual administrative actions

Monitoring Recommendations

• Enable logging on network perimeter devices to capture traffic to and from Totolink router management interfaces
• Configure alerts for any access to router CGI interfaces from non-administrative network segments
• Regularly review device configurations for unauthorized changes that may indicate compromise
• Implement network segmentation to limit exposure of router management interfaces

How to Mitigate CVE-2024-0576

Immediate Actions Required

• Restrict network access to the router's web management interface to trusted IP addresses only
• Disable remote administration if not required for operational purposes
• Place the router behind a firewall that blocks external access to management ports
• Monitor for and apply any firmware updates from Totolink addressing this vulnerability

Patch Information

As of the last modification date (2024-11-21), the vendor (Totolink) was contacted about this vulnerability but did not respond. No official patch has been confirmed. Affected users should monitor the VulDB advisory and Totolink's official support channels for updates.

SentinelOne Singularity provides comprehensive network visibility and can detect exploitation attempts targeting embedded devices. Organizations should leverage endpoint detection and response (EDR) capabilities to identify any lateral movement or post-exploitation activity originating from compromised network devices.

Workarounds

• Implement access control lists (ACLs) on upstream network devices to restrict access to the router's management interface
• Use a VPN or jump host for administrative access instead of exposing the management interface directly
• Consider replacing the affected device with an alternative router from a vendor with better security response practices
• Deploy network-level web application firewall (WAF) rules to filter requests with oversized parameters targeting CGI endpoints

# Example iptables rule to restrict access to router management interface
# Apply on upstream 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
iptables -A FORWARD -s <TRUSTED_ADMIN_IP> -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT
iptables -A FORWARD -s <TRUSTED_ADMIN_IP> -d <ROUTER_IP> -p tcp --dport 443 -j ACCEPT