CVE-2024-1003: Totolink N200re Buffer Overflow Vulnerability

CVE-2024-1003 Overview

CVE-2024-1003 is a stack-based buffer overflow vulnerability in the Totolink N200RE router running firmware version 9.3.5u.6139_B20201216. The flaw resides in the setLanguageCfg function within /cgi-bin/cstecgi.cgi. Attackers can trigger the overflow by manipulating the lang argument sent to the CGI endpoint. The vulnerability is exploitable remotely over the network and requires only low-privilege authentication. Public exploit details have been disclosed, increasing the risk of opportunistic attacks against exposed devices. The vendor was contacted before public disclosure but did not respond.

Critical Impact
Remote attackers with low-level privileges can corrupt stack memory, potentially achieving arbitrary code execution or denial of service on affected N200RE routers.

Affected Products

Totolink N200RE hardware router
Totolink N200RE firmware version 9.3.5u.6139_B20201216
The vulnerable setLanguageCfg handler in /cgi-bin/cstecgi.cgi

Discovery Timeline

2024-01-29 - CVE-2024-1003 published to the National Vulnerability Database
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2024-1003

Vulnerability Analysis

The vulnerability is a classic stack-based buffer overflow [CWE-121] affecting the setLanguageCfg handler in the Totolink N200RE web management interface. The CGI binary cstecgi.cgi processes HTTP requests and dispatches them to internal handler functions based on the requested action. When setLanguageCfg is invoked, the handler reads the lang parameter from the request body and copies it into a fixed-size stack buffer without validating the length of the input.

Because the copy operation lacks bounds checking, an attacker who submits an oversized lang value can overwrite adjacent stack memory. This includes saved return addresses and stack canary values on the MIPS-based firmware. Successful exploitation allows the attacker to control the program counter and redirect execution. On embedded routers of this class, memory protections such as ASLR and non-executable stacks are often absent or incomplete, making reliable code execution feasible.

Successful exploitation compromises confidentiality, integrity, and availability of the device. An attacker can pivot into the internal network, intercept traffic, or brick the router. Refer to the Jylsec Vulnerability Analysis for the detailed technical write-up.

Root Cause

The root cause is the absence of length validation on the lang parameter before it is copied into a stack-allocated buffer. The handler uses an unsafe string copy routine such as strcpy or sprintf without enforcing an upper bound. This design flaw is common in embedded router firmware, where developers often trust input from authenticated management interfaces.

Attack Vector

An attacker sends a crafted HTTP POST request to /cgi-bin/cstecgi.cgi targeting the setLanguageCfg topicurl. The request body includes an overlong lang field. Because the vulnerability requires low-privilege authentication, an attacker with valid or default credentials, or one who has obtained credentials through other means, can trigger the overflow. Devices exposed to the internet or accessible via lateral movement are at highest risk.

No verified proof-of-concept code is included here. See the Jylsec Vulnerability Analysis and VulDB entry #252272 for the full technical breakdown of the exploit primitive.

Detection Methods for CVE-2024-1003

Indicators of Compromise

HTTP POST requests to /cgi-bin/cstecgi.cgi containing a topicurl value of setLanguageCfg with an unusually long lang parameter.
Unexpected router reboots, crashes of the web management daemon, or corrupted configuration state on N200RE devices.
Outbound connections from the router to unknown external hosts following administrative login events.

Detection Strategies

Inspect network traffic destined for router management interfaces and flag requests to cstecgi.cgi where parameter lengths exceed reasonable configuration values.
Deploy signatures in network intrusion detection systems that match oversized lang parameters in POST bodies targeting Totolink CGI endpoints.
Correlate management-plane authentication events with subsequent anomalous router behavior such as service restarts or configuration drift.

Monitoring Recommendations

Enable syslog forwarding from the router to a centralized logging platform and monitor for repeated CGI errors or crashes.
Track EPSS trends for CVE-2024-1003, which currently sits at 1.25% (66.6th percentile) and may rise if weaponized exploits surface.
Audit administrative access to the router on a recurring basis and alert on management logins from unexpected source addresses.

How to Mitigate CVE-2024-1003

Immediate Actions Required

Restrict access to the router's web management interface to trusted internal networks only and disable WAN-side administration.
Rotate administrative credentials on all N200RE devices and enforce strong, unique passwords to reduce the risk of low-privilege exploitation.
Inventory all N200RE units running firmware 9.3.5u.6139_B20201216 and prioritize network segmentation of unpatched devices.

Patch Information

No vendor patch is currently available. According to the disclosure record, Totolink was contacted before public disclosure but did not respond. Organizations should treat affected devices as end-of-support until Totolink publishes fixed firmware. Consider replacing the N200RE with actively maintained hardware if a patch does not materialize.

Workarounds

Place N200RE routers behind a firewall that blocks unauthenticated and untrusted access to TCP ports serving the web management interface.
Disable remote management features and any UPnP or exposed CGI functionality that is not required for operations.
Monitor router traffic through an upstream inspection point and drop HTTP requests containing oversized parameters directed at cstecgi.cgi.

bash

# Example iptables rule to restrict router management access to a trusted subnet
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP