CVE-2026-5567: Tenda M3 Buffer Overflow Vulnerability

CVE-2026-5567 Overview

A buffer overflow vulnerability has been identified in Tenda M3 firmware version 1.0.0.10. This vulnerability affects the setAdvPolicyData function within the /goform/setAdvPolicyData endpoint of the Destination Handler component. By manipulating the policyType argument, an attacker can trigger a buffer overflow condition that may lead to remote code execution or denial of service.

Critical Impact

Remote attackers with low privileges can exploit this buffer overflow vulnerability over the network to potentially execute arbitrary code or crash the device, compromising network infrastructure security.

Affected Products

• Tenda M3 firmware version 1.0.0.10
• Tenda M3 routers running vulnerable Destination Handler component
• Network environments utilizing affected Tenda M3 devices

Discovery Timeline

• 2026-04-05 - CVE-2026-5567 published to NVD
• 2026-04-07 - Last updated in NVD database

Technical Details for CVE-2026-5567

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the setAdvPolicyData function, which handles policy configuration data within the Tenda M3 router's web management interface. When processing the policyType argument, the function fails to properly validate input boundaries, allowing an attacker to write data beyond the allocated buffer space.

The exploit has been publicly disclosed, increasing the urgency for mitigation. Successful exploitation could allow attackers to overwrite adjacent memory regions, potentially leading to arbitrary code execution with device-level privileges or causing device instability and denial of service conditions.

Root Cause

The root cause of this vulnerability is improper bounds checking in the setAdvPolicyData function when handling the policyType parameter. The function does not adequately validate the length or content of user-supplied input before copying it into a fixed-size buffer, resulting in a classic buffer overflow condition. This lack of input validation is a common issue in embedded device firmware where memory constraints often lead to unsafe memory handling practices.

Attack Vector

The attack vector is network-based, allowing remote exploitation without physical access to the device. An authenticated attacker with low privileges can send a specially crafted HTTP request to the /goform/setAdvPolicyData endpoint with a malicious policyType value. The crafted input exceeds the expected buffer size, causing memory corruption that can be leveraged to hijack program execution flow or crash the device.

The vulnerability can be exploited by sending a manipulated POST request to the vulnerable endpoint. The attack targets the policyType parameter with oversized or specially crafted input data designed to overflow the destination buffer. For detailed technical information about the exploitation mechanism, refer to the GitHub CVE Issue Discussion and VulDB #355337.

Detection Methods for CVE-2026-5567

Indicators of Compromise

• Unusual HTTP POST requests to /goform/setAdvPolicyData with abnormally large policyType parameter values
• Device crashes or unexpected reboots of Tenda M3 routers
• Memory corruption errors or segmentation faults in device logs
• Suspicious network traffic patterns targeting Tenda router management interfaces

Detection Strategies

• Implement network intrusion detection rules to monitor for oversized HTTP parameters targeting /goform/setAdvPolicyData
• Deploy web application firewall (WAF) rules to block requests with abnormally long policyType values
• Enable logging on network devices to capture and analyze requests to Tenda router management interfaces
• Use endpoint detection and response (EDR) solutions to monitor for exploitation attempts against IoT devices

Monitoring Recommendations

• Monitor network traffic for repeated failed or malformed requests to Tenda M3 web management endpoints
• Configure alerting for device instability indicators such as unexpected reboots or connectivity loss
• Implement network segmentation monitoring to detect lateral movement following potential device compromise
• Review access logs for authentication attempts from unexpected IP addresses targeting router administration

How to Mitigate CVE-2026-5567

Immediate Actions Required

• Restrict network access to Tenda M3 management interfaces to trusted IP addresses only
• Disable remote management if not required for operations
• Implement network segmentation to isolate vulnerable devices from critical network segments
• Monitor for firmware updates from Tenda and apply patches when available

Patch Information

At the time of publication, no official patch has been released by Tenda. Organizations should monitor the Tenda Official Website for firmware updates addressing this vulnerability. Until a patch is available, implement the recommended workarounds to reduce exposure.

Workarounds

• Configure firewall rules to block external access to port 80/443 on Tenda M3 devices
• Implement access control lists (ACLs) limiting management interface access to authorized administrators only
• Deploy a VPN requirement for remote administration of affected devices
• Consider temporary device replacement with unaffected alternatives in high-security environments

# Example firewall rule to restrict access to Tenda M3 management interface
# Replace 192.168.1.100 with your Tenda M3 device IP
# Replace 10.0.0.0/24 with your trusted management network

iptables -A INPUT -d 192.168.1.100 -p tcp --dport 80 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -d 192.168.1.100 -p tcp --dport 80 -j DROP
iptables -A INPUT -d 192.168.1.100 -p tcp --dport 443 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -d 192.168.1.100 -p tcp --dport 443 -j DROP