Tenda M3 Router Buffer Overflow Vulnerability

A critical buffer overflow vulnerability has been identified in Tenda M3 router version 1.0.0.10. The vulnerability resides in the setAdvPolicyData function within the /goform/setAdvPolicyData file, a part of the Destination Handler component. By manipulating the policyType argument, a remote attacker can trigger a buffer overflow, potentially leading to arbitrary code execution. Publicly available exploit code exists, increasing the risk of exploitation. This vulnerability poses a significant threat to organizations utilizing the affected Tenda M3 router, potentially allowing attackers to gain unauthorized access to the network or disrupt services.

Attack Chain

1. Attacker identifies a vulnerable Tenda M3 router exposed to the internet or reachable from their network position.
2. Attacker sends a crafted HTTP POST request to /goform/setAdvPolicyData.
3. The POST request includes a malicious policyType argument designed to overflow the buffer in the setAdvPolicyData function.
4. The setAdvPolicyData function in /goform/setAdvPolicyData processes the policyType argument without proper bounds checking.
5. The excessive data provided in the policyType argument overwrites adjacent memory regions.
6. The attacker carefully crafts the overflow to overwrite critical data or inject malicious code into the process’s memory space.
7. The injected code is executed, giving the attacker control over the router.
8. The attacker can then use the compromised router as a foothold to pivot to other devices on the network, exfiltrate sensitive data, or cause denial of service.

Impact

Successful exploitation of this buffer overflow vulnerability allows a remote attacker to execute arbitrary code on the Tenda M3 router. This could lead to a complete compromise of the device, allowing the attacker to control network traffic, access sensitive information, or use the router as a launchpad for further attacks within the network. Given the severity and the existence of public exploits, vulnerable routers are at high risk of being targeted.

Recommendation

• Apply any available firmware updates from Tenda to patch CVE-2026-5567.
• Monitor web server logs for suspicious POST requests to /goform/setAdvPolicyData with unusually long policyType arguments; deploy the Sigma rule Detect Suspicious PolicyType Argument Length to identify this activity.
• Implement network segmentation to limit the potential impact of a compromised router.
• Consider using a web application firewall (WAF) to filter malicious requests targeting the affected endpoint.
• Review and restrict access to the router’s management interface to authorized personnel only.