CVE-2025-55852: Tenda AC8 Buffer Overflow Vulnerability

CVE-2025-55852 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda AC8 wireless router firmware version 16.03.34.06. The vulnerability exists in the formWifiBasicSet function, which fails to properly validate the length of user-supplied input through the security or security_5g parameters. This buffer overflow condition can be exploited remotely over the network without authentication, potentially allowing attackers to crash the device and cause a denial of service condition.

Critical Impact

Network-accessible buffer overflow in a consumer wireless router that can be exploited without authentication to cause device crashes and network disruption.

Affected Products

• Tenda AC8 Firmware version 16.03.34.06
• Tenda AC8 Hardware version 4.0
• Tenda AC8 wireless routers running vulnerable firmware

Discovery Timeline

• 2025-09-03 - CVE-2025-55852 published to NVD
• 2025-09-08 - Last updated in NVD database

Technical Details for CVE-2025-55852

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow). The formWifiBasicSet function in the Tenda AC8 firmware processes wireless configuration requests including security settings for both 2.4GHz and 5GHz bands. The function accepts the security and security_5g parameters from HTTP requests but fails to implement proper bounds checking before copying user-supplied data into fixed-size stack buffers.

When an attacker sends a specially crafted HTTP request with oversized values for these parameters, the excess data overflows the allocated buffer space on the stack. This memory corruption condition affects device availability, allowing remote attackers to crash the router without requiring any form of authentication.

Root Cause

The root cause of this vulnerability is improper input validation in the firmware's web interface handler. The formWifiBasicSet function uses unsafe memory copy operations that do not verify the input length against the destination buffer size. This is a common weakness in embedded device firmware where memory-safe programming practices are not consistently applied.

Attack Vector

The attack vector is network-based, requiring the attacker to have network access to the router's web management interface. The vulnerability can be triggered by sending a malformed HTTP POST request to the formWifiBasicSet endpoint with an excessively long string in either the security or security_5g parameter.

The attack does not require authentication, making any Tenda AC8 router with the vulnerable firmware and an accessible management interface a potential target. Attackers on the local network or those who can reach the management interface remotely (if exposed) can exploit this vulnerability.

The vulnerability mechanism involves sending an HTTP request to the wireless configuration endpoint with oversized parameter values. When the formWifiBasicSet function processes these malformed inputs without proper length validation, the data overflows the stack buffer, corrupting adjacent memory and causing the device to crash. For detailed technical analysis, refer to the GitHub IoT Device Analysis.

Detection Methods for CVE-2025-55852

Indicators of Compromise

• Unexpected router reboots or crashes without apparent cause
• HTTP requests to /goform/formWifiBasicSet with abnormally large parameter values
• Network connectivity interruptions coinciding with management interface access attempts
• Log entries showing malformed requests to wireless configuration endpoints

Detection Strategies

• Monitor HTTP traffic to the router's management interface for requests with unusually large POST body sizes
• Implement network-based intrusion detection rules to identify buffer overflow attack patterns targeting Tenda devices
• Configure alerts for repeated router restarts or unavailability events
• Deploy network segmentation to isolate management interfaces and monitor cross-segment traffic

Monitoring Recommendations

• Enable logging on the router if supported and review for anomalous configuration change attempts
• Monitor for network scanning activity targeting common router management ports (80, 443)
• Implement continuous network monitoring to detect device unavailability patterns
• Use network traffic analysis tools to identify exploit attempts against IoT devices

How to Mitigate CVE-2025-55852

Immediate Actions Required

• Restrict access to the router's web management interface to trusted networks only
• Disable remote management if not explicitly required
• Implement firewall rules to block external access to the router's management ports
• Monitor for firmware updates from Tenda and apply them when available

Patch Information

At the time of this analysis, no official patch information is available from Tenda. Organizations should monitor the vendor's official channels for security updates addressing this vulnerability. The GitHub IoT Device Analysis provides additional technical context regarding the vulnerability.

Workarounds

• Configure the router's management interface to be accessible only from specific trusted IP addresses
• Place the router behind an additional firewall that filters access to management services
• Consider replacing affected devices with alternative hardware if no patch becomes available
• Implement network segmentation to limit the blast radius if the device is compromised

# Example: Restrict management access using upstream firewall (iptables)
# Block external access to router management interface
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 access only from trusted admin workstation
iptables -I FORWARD -s <admin_ip> -d <router_ip> -p tcp --dport 80 -j ACCEPT