CVE-2026-4905: Tenda AC5 Buffer Overflow Vulnerability

CVE-2026-4905 Overview

A critical stack-based buffer overflow vulnerability has been identified in Tenda AC5 router firmware version 15.03.06.47. The vulnerability exists in the formWifiWpsOOB function within the POST Request Handler component, specifically in the /goform/WifiWpsOOB endpoint. Attackers can exploit this flaw by manipulating the index argument, leading to a stack-based buffer overflow condition that enables remote code execution.

Critical Impact

This vulnerability allows remote attackers with low privileges to achieve complete compromise of affected Tenda AC5 routers, potentially enabling network-wide attacks, traffic interception, and persistent unauthorized access to connected networks.

Affected Products

• Tenda AC5 Firmware version 15.03.06.47
• Tenda AC5 Hardware version 1.0

Discovery Timeline

• 2026-03-27 - CVE-2026-4905 published to NVD
• 2026-03-31 - Last updated in NVD database

Technical Details for CVE-2026-4905

Vulnerability Analysis

The vulnerability resides in the formWifiWpsOOB function that handles POST requests to the /goform/WifiWpsOOB endpoint on Tenda AC5 routers. This function processes user-supplied input through the index parameter without proper bounds checking, creating a classic stack-based buffer overflow condition.

When a malicious request is submitted with an oversized or specially crafted index argument, the function fails to validate the input length before copying it to a fixed-size stack buffer. This allows an attacker to overwrite adjacent stack memory, including the return address, potentially achieving arbitrary code execution with the privileges of the web server process.

The vulnerability is classified under CWE-787 (Out-of-Bounds Write) and CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). Exploitation is achievable remotely over the network with only low-level authentication required, making it a significant threat to home and small business networks using affected devices.

Root Cause

The root cause of this vulnerability is insufficient input validation in the formWifiWpsOOB function. The function accepts user-controlled data via the index parameter and copies it to a stack-allocated buffer without verifying that the input length does not exceed the buffer's capacity. This lack of boundary checking is a fundamental memory safety issue common in embedded device firmware written in C/C++.

Attack Vector

The attack is carried out remotely over the network by sending a specially crafted HTTP POST request to the /goform/WifiWpsOOB endpoint. The attacker manipulates the index parameter to include malicious payload data that overflows the stack buffer. By carefully crafting the overflow data, an attacker can overwrite the saved return address on the stack and redirect program execution to attacker-controlled code or existing code gadgets (ROP chains).

The vulnerability can be exploited by authenticated users with low-level privileges, as the affected endpoint does not require administrative access. The exploit has been publicly disclosed, increasing the risk of widespread exploitation against unpatched devices.

Detection Methods for CVE-2026-4905

Indicators of Compromise

• Unusual HTTP POST requests targeting /goform/WifiWpsOOB with abnormally long index parameter values
• Unexpected router reboots or service crashes indicating exploitation attempts
• Unauthorized configuration changes to router settings or firmware
• Suspicious outbound network connections originating from the router device

Detection Strategies

• Monitor network traffic for HTTP POST requests to /goform/WifiWpsOOB containing oversized payloads
• Implement intrusion detection rules to flag requests with index parameters exceeding expected length thresholds
• Review router access logs for repeated failed authentication attempts or unusual request patterns
• Deploy network-based anomaly detection to identify buffer overflow exploitation signatures

Monitoring Recommendations

• Enable verbose logging on Tenda AC5 devices if supported by firmware
• Monitor router management interface access logs for unauthorized connections
• Implement network segmentation to isolate IoT devices from critical infrastructure
• Use SentinelOne Singularity to monitor for post-exploitation activities on networked systems

How to Mitigate CVE-2026-4905

Immediate Actions Required

• Restrict access to the router's web management interface to trusted networks only
• Disable remote management features if not required for operations
• Implement network firewall rules to block external access to port 80/443 on the router
• Consider replacing affected devices with routers from vendors that provide timely security updates

Patch Information

As of the last NVD update on 2026-03-31, no official patch has been released by Tenda for this vulnerability. Users should monitor the Tenda Official Website for firmware updates and security advisories. Additional technical details can be found in the VulDB entry and the vulnerability documentation.

Workarounds

• Configure access control lists (ACLs) to limit management interface access to specific IP addresses
• Place the router behind an additional firewall that can filter malicious requests
• Use a VPN for remote management instead of exposing the web interface directly
• Disable WPS functionality entirely if not required for network operations

# Network isolation configuration example (upstream firewall)
# Block external access to router management interface
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 443 -j DROP
# Allow only trusted management subnet
iptables -A FORWARD -s 10.0.0.0/24 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT