CVE-2025-6302: Totolink EX1200T Buffer Overflow Flaw

CVE-2025-6302 Overview

CVE-2025-6302 is a stack-based buffer overflow in the TOTOLINK EX1200T Wi-Fi range extender running firmware version 4.1.2cu.5232_B20210713. The flaw resides in the setStaticDhcpConfig function within /cgi-bin/cstecgi.cgi. Attackers manipulate the Comment argument to overflow a fixed-size stack buffer. The vulnerability is exploitable remotely over the network and the exploit details are publicly 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-privileged access can corrupt stack memory on TOTOLINK EX1200T devices, potentially achieving arbitrary code execution on the embedded router.

Affected Products

TOTOLINK EX1200T hardware device
TOTOLINK EX1200T firmware 4.1.2cu.5232_B20210713
Deployments exposing the /cgi-bin/cstecgi.cgi web management endpoint

Discovery Timeline

2025-06-20 - CVE-2025-6302 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-6302

Vulnerability Analysis

The TOTOLINK EX1200T exposes a CGI-based management interface through cstecgi.cgi. The setStaticDhcpConfig handler processes static DHCP reservation requests submitted by authenticated users. The function copies the user-supplied Comment parameter into a fixed-size stack buffer without verifying input length. Supplying an oversized Comment value overruns the buffer and overwrites adjacent stack memory, including the saved return address. The exploit has been disclosed publicly, increasing the likelihood of weaponization against exposed devices.

Root Cause

The root cause is improper bounds checking on the Comment argument inside setStaticDhcpConfig. The CGI handler uses an unsafe string copy operation against a stack-allocated destination buffer. No length validation precedes the copy, allowing attacker-controlled data to extend beyond the buffer boundary. This pattern matches [CWE-119] memory corruption flaws common in MIPS-based embedded router firmware.

Attack Vector

The attack vector is network-based and requires low-privileged authentication to reach the CGI endpoint. An attacker sends a crafted HTTP POST request to /cgi-bin/cstecgi.cgi invoking the setStaticDhcpConfig action with an oversized Comment field. The malformed request triggers the stack overflow and corrupts execution flow. Successful exploitation can yield arbitrary code execution under the privileges of the web server process, typically running as root on consumer router firmware. Refer to the public technical write-up and VulDB entry #313302 for additional detail.

// No verified exploit code is published in the enriched data set.
// See the linked technical references for proof-of-concept details.

Detection Methods for CVE-2025-6302

Indicators of Compromise

HTTP POST requests to /cgi-bin/cstecgi.cgi containing the setStaticDhcpConfig action with abnormally long Comment values
Unexpected reboots, crashes, or service restarts on TOTOLINK EX1200T devices following inbound HTTP traffic
Outbound connections from the router to unfamiliar command-and-control infrastructure after suspicious management-plane requests

Detection Strategies

Inspect network traffic to router management interfaces for cstecgi.cgi requests with Comment parameters exceeding reasonable length thresholds
Alert on any external-source HTTP traffic reaching the EX1200T management endpoint, which should be LAN-restricted
Correlate router syslog entries indicating process crashes with prior HTTP requests to the CGI handler

Monitoring Recommendations

Capture and retain web access logs from the router when remote management is enabled
Forward router telemetry to a central log analytics platform for retention and search
Monitor DNS and NetFlow data from router-attached segments for anomalous egress patterns

How to Mitigate CVE-2025-6302

Immediate Actions Required

Disable WAN-side remote management on the TOTOLINK EX1200T until a patched firmware release is available
Restrict access to /cgi-bin/cstecgi.cgi to trusted management workstations on the LAN
Rotate administrative credentials to reduce the chance of low-privileged exploitation
Inventory all TOTOLINK EX1200T devices running firmware 4.1.2cu.5232_B20210713

Patch Information

No vendor patch is referenced in the enriched data at the time of writing. Monitor the TOTOLINK official website for firmware updates addressing the setStaticDhcpConfig overflow. Consider replacing end-of-support hardware with vendor-maintained equivalents if no fix is released.

Workarounds

Place affected devices behind a perimeter firewall that blocks inbound HTTP and HTTPS to the router management interface
Segment the router onto a dedicated management VLAN with explicit access control lists
Disable any port-forwarding or UPnP rules that expose the CGI endpoint to untrusted networks

bash

# Example iptables rule to restrict CGI access to a management subnet
iptables -A INPUT -p tcp --dport 80 -s 192.0.2.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP