CVE-2025-69700: Tenda FH1203 Buffer Overflow Vulnerability

CVE-2025-69700 Overview

CVE-2025-69700 is a stack-based buffer overflow vulnerability in Tenda FH1203 V2.0.1.6 routers. The flaw resides in the modify_add_client_prio function and is reachable through the formSetClientPrio CGI handler. Remote attackers can send a crafted HTTP request to the router's web management interface to trigger memory corruption on the stack. Successful exploitation results in a denial of service condition on the affected device. The vulnerability is classified under [CWE-121] Stack-based Buffer Overflow and requires no authentication or user interaction.

Critical Impact
Unauthenticated remote attackers can crash the Tenda FH1203 router by sending malformed input to the formSetClientPrio endpoint, disrupting network availability.

Affected Products

Tenda FH1203 router (hardware)
Tenda FH1203 firmware version 2.0.1.6
Devices exposing the web management CGI interface

Discovery Timeline

2026-02-23 - CVE-2025-69700 published to NVD
2026-02-24 - Last updated in NVD database

Technical Details for CVE-2025-69700

Vulnerability Analysis

The vulnerability resides in the modify_add_client_prio function within the firmware's HTTP request handler. When the formSetClientPrio CGI endpoint receives client priority configuration data, the function copies attacker-controlled input into a fixed-size stack buffer without validating the input length. The overflow corrupts adjacent stack memory, including saved return addresses and frame pointers on the MIPS-based device.

Because the web management interface accepts the request without authentication on vulnerable configurations, the attack vector is fully network-based. The impact is limited to availability, with the router process crashing or hanging when the malformed request is processed. Confidentiality and integrity of stored data are not directly affected.

Root Cause

The root cause is missing bounds checking in modify_add_client_prio when handling parameters supplied through formSetClientPrio. The function uses unsafe string copy operations against a fixed-length stack buffer, a recurring pattern in Tenda SOHO router firmware. Standard compiler-level stack canaries and address space layout randomization (ASLR) are typically absent or weakly enforced on these embedded MIPS targets.

Attack Vector

An unauthenticated remote attacker sends a crafted HTTP POST request to the router's web management interface, targeting the formSetClientPrio handler with an oversized parameter value. The malformed input flows into modify_add_client_prio, overflowing the destination buffer and corrupting the call stack. The resulting crash takes the device offline until it is restarted.

// Conceptual flow (no verified PoC code published)
// POST /goform/formSetClientPrio HTTP/1.1
// Host: <router-ip>
// Content-Type: application/x-www-form-urlencoded
//
// <oversized parameter consumed by modify_add_client_prio>
//
// Reference: https://github.com/xhh0124/SemVulLLM

Detection Methods for CVE-2025-69700

Indicators of Compromise

Unexpected reboots or unreachable web management interface on Tenda FH1203 devices
Inbound HTTP POST requests targeting /goform/formSetClientPrio with abnormally long parameter values
Repeated TCP resets or connection failures from the router's HTTP service following crafted requests

Detection Strategies

Inspect HTTP traffic to the router management interface for POST requests to formSetClientPrio containing parameter lengths beyond expected limits
Use intrusion detection signatures that flag oversized query parameters directed at Tenda /goform/ CGI endpoints
Correlate router availability loss with preceding inbound HTTP requests from non-administrative source addresses

Monitoring Recommendations

Log all administrative access attempts to the router's HTTP interface and alert on requests originating from untrusted networks
Monitor SNMP or ICMP reachability of the FH1203 to detect crash-induced downtime
Track repeat connection attempts to /goform/formSetClientPrio from a single source within short time windows

How to Mitigate CVE-2025-69700

Immediate Actions Required

Restrict access to the router's web management interface to trusted internal management VLANs only
Disable remote WAN-side administration on the FH1203 if currently enabled
Place vulnerable devices behind a network filter that blocks external HTTP requests to /goform/ endpoints

Patch Information

No vendor advisory or firmware fix has been published in the referenced data for CVE-2025-69700. Administrators should monitor the Tenda official support site for an updated firmware release beyond version 2.0.1.6. Technical details for the issue are referenced in the GitHub PoC Repository.

Workarounds

Block inbound traffic to TCP ports 80 and 443 on the router from untrusted networks using upstream firewall rules
Segment management traffic from user traffic so only authorized administrators can reach the CGI interface
Replace end-of-life or unpatched FH1203 units with supported devices that receive active security updates

bash

# Example: restrict HTTP management access to a trusted subnet only
iptables -I INPUT -p tcp --dport 80 ! -s 192.168.10.0/24 -j DROP
iptables -I INPUT -p tcp --dport 443 ! -s 192.168.10.0/24 -j DROP