CVE-2025-69700: Tenda FH1203 Buffer Overflow Vulnerability

CVE-2025-69700 Overview

CVE-2025-69700 is a stack-based buffer overflow vulnerability affecting Tenda FH1203 V2.0.1.6 wireless routers. The vulnerability exists in the modify_add_client_prio function, which is accessible through the formSetClientPrio CGI handler. This firmware vulnerability allows remote attackers to trigger a denial of service condition by sending specially crafted requests to the affected device without requiring authentication.

Critical Impact

Unauthenticated remote attackers can exploit this stack-based buffer overflow to crash affected Tenda FH1203 devices, causing network disruption for all connected users.

Affected Products

• Tenda FH1203 Firmware Version 2.0.1.6
• Tenda FH1203 Hardware Device
• Tenda FH1203 Firmware (all builds of V2.0.1.6)

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

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), a memory corruption flaw that occurs when a program writes data beyond the boundaries of a stack-allocated buffer. The affected function modify_add_client_prio fails to properly validate the length of user-supplied input before copying it to a fixed-size buffer on the stack.

The vulnerability is network-accessible without requiring any privileges or user interaction, making it particularly dangerous for consumer-grade networking equipment that is often deployed at network perimeters. Exploitation results in denial of service, potentially crashing the device and interrupting network connectivity for all users relying on the affected router.

Root Cause

The root cause lies in insufficient bounds checking within the modify_add_client_prio function. When processing client priority configuration requests through the formSetClientPrio CGI endpoint, the function copies user-supplied data into a stack buffer without verifying that the input length does not exceed the buffer's allocated size. This allows an attacker to overflow the buffer and corrupt adjacent stack memory, leading to a crash.

Attack Vector

The attack is conducted over the network by sending a maliciously crafted HTTP request to the formSetClientPrio CGI handler on the Tenda FH1203 router's web management interface. Since no authentication is required and the attack complexity is low, any attacker with network access to the device's management interface can trigger the vulnerability.

The attacker constructs an HTTP request containing an oversized payload in the parameter processed by modify_add_client_prio. When the device processes this request, the stack buffer overflows, corrupting memory and causing the device to crash or become unresponsive.

Technical details and proof-of-concept information can be found in the GitHub PoC Repository.

Detection Methods for CVE-2025-69700

Indicators of Compromise

• Unexpected router reboots or crashes coinciding with unusual HTTP traffic to the management interface
• HTTP requests to /goform/formSetClientPrio containing abnormally large parameter values
• Network connectivity interruptions affecting multiple devices simultaneously
• Crash logs on the Tenda FH1203 indicating memory corruption or stack overflow events

Detection Strategies

• Monitor HTTP traffic to the router's web interface for requests targeting the formSetClientPrio CGI endpoint with unusually large payloads
• Implement network intrusion detection rules to flag HTTP requests to Tenda router management interfaces containing oversized POST data
• Enable logging on upstream network devices to capture traffic patterns consistent with exploitation attempts
• Deploy SentinelOne Singularity for IoT to detect anomalous behavior patterns on network devices

Monitoring Recommendations

• Establish baseline network behavior for management interface traffic and alert on deviations
• Configure network monitoring to track device availability and flag unexpected restarts of Tenda routers
• Implement automated health checks for critical network infrastructure devices
• Review firewall logs for repeated connection attempts to router management interfaces from untrusted sources

How to Mitigate CVE-2025-69700

Immediate Actions Required

• Restrict access to the Tenda FH1203 web management interface to trusted IP addresses only using firewall rules
• Disable remote management access if not required for operations
• Segment the network to isolate management interfaces from untrusted network segments
• Consider replacing affected devices with alternative hardware if vendor patches are unavailable

Patch Information

No vendor-provided security patch has been identified in the available CVE data. Tenda has not released an official advisory or firmware update addressing this vulnerability as of the last NVD update. Organizations should monitor the GitHub PoC Repository and Tenda's official support channels for updates.

Workarounds

• Configure access control lists (ACLs) on upstream routers or firewalls to block external access to the router's management interface
• Use a separate management VLAN to isolate administrative access from general network traffic
• Disable the web management interface entirely if command-line or other management methods are available and sufficient
• Implement network-level rate limiting to reduce the impact of potential exploitation attempts

# Example: Restrict management interface access using iptables on upstream device
# Allow management access only from trusted admin subnet
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -s 192.168.100.0/24 -j ACCEPT
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP