CVE-2026-4906: Tenda AC5 Buffer Overflow Vulnerability

CVE-2026-4906 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda AC5 firmware version 15.03.06.47. The vulnerability exists in the decodePwd function within the /goform/WizardHandle endpoint of the POST Request Handler component. An attacker can exploit this vulnerability by manipulating the WANT or WANS parameters, leading to memory corruption that could enable remote code execution or denial of service conditions.

Critical Impact

This network-accessible vulnerability in Tenda AC5 routers allows authenticated attackers to trigger a stack-based buffer overflow, potentially compromising the entire device and network infrastructure it manages.

Affected Products

• Tenda AC5 Firmware version 15.03.06.47
• Tenda AC5 Hardware version 1.0
• Tenda AC5 devices running vulnerable firmware

Discovery Timeline

• 2026-03-27 - CVE-2026-4906 published to NVD
• 2026-03-31 - Last updated in NVD database

Technical Details for CVE-2026-4906

Vulnerability Analysis

This vulnerability is classified as a stack-based buffer overflow (CWE-787: Out-of-bounds Write) with an associated memory buffer boundary violation (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the decodePwd function, which processes incoming POST request data sent to the /goform/WizardHandle endpoint on the device's web management interface.

The vulnerability can be exploited remotely over the network and requires low-privilege authentication to trigger. Once exploited, an attacker could achieve high impact across confidentiality, integrity, and availability of the affected device. The exploit details have been publicly disclosed, increasing the urgency for remediation.

Root Cause

The root cause of this vulnerability lies in insufficient bounds checking within the decodePwd function when processing the WANT and WANS parameters from user-supplied POST request data. The function fails to properly validate the length of input data before copying it into a fixed-size stack buffer, allowing an attacker to overflow the buffer and overwrite adjacent memory regions including the function return address.

Attack Vector

The attack is network-based and targets the web management interface of the Tenda AC5 router. An attacker with low-level access can send a specially crafted POST request to the /goform/WizardHandle endpoint with oversized WANT or WANS parameter values. When the decodePwd function processes these malformed parameters, the stack buffer overflow occurs, potentially allowing the attacker to hijack program execution flow.

The vulnerability mechanism involves sending an HTTP POST request to the affected endpoint with manipulated parameter values that exceed expected buffer sizes. When processed by the decodePwd function, the oversized input overflows the stack buffer. For detailed technical analysis, refer to the Notion Documentation Guide and VulDB entry #353657.

Detection Methods for CVE-2026-4906

Indicators of Compromise

• Unusual HTTP POST requests to /goform/WizardHandle with abnormally large WANT or WANS parameter values
• Router crashes or unexpected reboots following web interface access
• Unexpected changes to router configuration or firmware
• Network traffic anomalies originating from the router's management interface

Detection Strategies

• Monitor HTTP traffic to the router's web management interface for POST requests targeting /goform/WizardHandle
• Implement network intrusion detection rules to flag oversized parameter values in web requests to Tenda AC5 devices
• Review web server logs on the device for signs of exploitation attempts or malformed requests
• Deploy network segmentation to isolate router management interfaces from untrusted networks

Monitoring Recommendations

• Enable logging on all Tenda AC5 devices and forward logs to a centralized SIEM solution
• Set up alerts for multiple failed authentication attempts followed by successful access to the web interface
• Monitor for firmware modification or configuration changes on affected devices
• Establish baseline network behavior for router management traffic to detect anomalies

How to Mitigate CVE-2026-4906

Immediate Actions Required

• Restrict access to the Tenda AC5 web management interface to trusted networks only
• Disable remote management features if not required
• Place affected routers behind a firewall that blocks external access to the management interface
• Implement strong authentication credentials and change default passwords

Patch Information

At the time of publication, no official patch from Tenda has been identified for this vulnerability. Organizations should monitor the Tenda Official Website for firmware updates addressing CVE-2026-4906. Given the public disclosure of this exploit, applying vendor patches immediately upon release is critical.

Workarounds

• Disable the web management interface if device administration is not required
• Implement network access control lists (ACLs) to restrict access to the /goform/WizardHandle endpoint
• Use a VPN to access router management functions rather than exposing the interface directly
• Consider replacing vulnerable devices with supported hardware if no patch becomes available

# Example: Restrict management interface access via iptables (on upstream firewall)
# Block external access to router management port (typically 80/443)
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 subnet
iptables -I FORWARD -s 192.168.1.0/24 -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT