CVE-2025-25663: Tenda AC8 Buffer Overflow Vulnerability

CVE-2025-25663 Overview

CVE-2025-25663 is a stack-based buffer overflow vulnerability affecting Tenda AC8V4 routers running firmware version V16.03.34.06. The vulnerability exists in the SUB_0046AC38 function within the /goform/WifiExtraSet endpoint. By manipulating the wpapsk_crypto argument, an unauthenticated remote attacker can trigger a stack-based buffer overflow, potentially leading to arbitrary code execution with elevated privileges on the affected device.

Critical Impact

This vulnerability allows unauthenticated remote attackers to execute arbitrary code on vulnerable Tenda AC8V4 routers, potentially leading to complete device compromise, network infiltration, and persistent backdoor installation.

Affected Products

• Tenda AC8 Firmware version 16.03.34.06
• Tenda AC8 Hardware version 4.0

Discovery Timeline

• 2025-02-20 - CVE-2025-25663 published to NVD
• 2025-03-17 - Last updated in NVD database

Technical Details for CVE-2025-25663

Vulnerability Analysis

This vulnerability is classified under CWE-787 (Out-of-bounds Write) and CWE-120 (Buffer Copy without Checking Size of Input). The affected function SUB_0046AC38 processes user-supplied input from the wpapsk_crypto parameter without properly validating the input length before copying it to a fixed-size stack buffer.

The /goform/WifiExtraSet endpoint is accessible over the network without authentication, which significantly increases the attack surface. When an attacker sends a specially crafted HTTP request with an oversized wpapsk_crypto value, the function copies this data onto the stack, overwriting adjacent memory regions including the return address. This allows attackers to hijack program execution flow and execute arbitrary code in the context of the router's web service process.

Root Cause

The root cause of this vulnerability is insufficient input validation in the SUB_0046AC38 function. The firmware fails to verify that the length of the wpapsk_crypto parameter does not exceed the allocated stack buffer size before performing the copy operation. This is a classic buffer overflow scenario where user-controlled data is copied to a fixed-size buffer without bounds checking, violating secure coding practices for embedded systems.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by sending a malicious HTTP POST request to the /goform/WifiExtraSet endpoint with an oversized wpapsk_crypto parameter. The attack can be executed remotely from any network segment that has access to the router's web management interface.

The exploitation process involves:

1. Crafting an HTTP POST request targeting /goform/WifiExtraSet
2. Including an excessively long wpapsk_crypto parameter value
3. Carefully constructing the payload to overwrite the return address with attacker-controlled values
4. Achieving code execution when the vulnerable function returns

For detailed technical information about this vulnerability, see the GitHub PoC Repository which contains proof-of-concept information.

Detection Methods for CVE-2025-25663

Indicators of Compromise

• Unexpected HTTP POST requests to /goform/WifiExtraSet with abnormally large wpapsk_crypto parameter values
• Router crashes, reboots, or unusual system instability
• Unexplained changes to router configuration or firmware
• Suspicious outbound network connections originating from the router
• Modified DNS settings or routing tables without administrator action

Detection Strategies

• Monitor HTTP traffic to the router's web interface for requests containing unusually long parameter values targeting /goform/WifiExtraSet
• Implement network intrusion detection rules to flag POST requests to Tenda router endpoints with payload sizes exceeding normal operational parameters
• Deploy endpoint detection and response (EDR) solutions capable of monitoring embedded device behavior for anomalous activity
• Review router access logs for repeated failed authentication attempts or unusual access patterns

Monitoring Recommendations

• Implement network segmentation to isolate IoT devices and routers from critical network segments
• Enable comprehensive logging on network firewalls to capture all traffic to and from router management interfaces
• Configure alerts for any modifications to router firmware or configuration files
• Regularly audit connected devices for unauthorized access or configuration changes

How to Mitigate CVE-2025-25663

Immediate Actions Required

• Disable remote management access to the router's web interface from untrusted networks immediately
• Place the affected Tenda AC8V4 router behind a firewall that blocks external access to the management interface
• Restrict access to the /goform/WifiExtraSet endpoint if possible through access control lists
• Consider replacing vulnerable devices with alternative hardware if no patch is available
• Monitor for any firmware updates from Tenda addressing this vulnerability

Patch Information

As of the last update on 2025-03-17, no official patch from Tenda has been confirmed for this vulnerability. Organizations should monitor Tenda's official support channels and security advisories for firmware updates addressing CVE-2025-25663. Until a patch is available, implementing the workarounds below is strongly recommended.

Workarounds

• Disable the web management interface entirely if it is not required for operations
• Configure firewall rules to block all external access to TCP ports used by the router's web interface (typically port 80 and 443)
• Implement network segmentation to isolate the router from sensitive network resources
• Consider using a VPN to access the router's management interface rather than exposing it directly
• Monitor the GitHub PoC Repository for updated technical details and potential mitigations

# Example: Block external access to router web interface using iptables on upstream firewall
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 443 -j DROP

# Allow management only from trusted admin workstation
iptables -I FORWARD -s <ADMIN_IP> -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT