CVE-2026-4961 is a stack-based buffer overflow vulnerability discovered in the Tenda AC6 router firmware version 15.03.05.16. The flaw resides in the formQuickIndex function within the POST request handler located at /goform/QuickIndex. Specifically, the vulnerability arises from improper handling of the PPPOEPassword argument, which can be manipulated by an attacker to overflow a stack buffer. This overflow can corrupt adjacent memory, potentially allowing remote attackers to execute arbitrary code on the device with elevated privileges. The vulnerability requires no authentication and no user interaction, making it highly exploitable over the network. The CVSS v4.0 base score is 8.7, reflecting its high severity due to network attack vector, low attack complexity, no privileges required, and no user interaction. The impact includes full compromise of the router, enabling attackers to intercept, modify, or disrupt network traffic, deploy malware, or pivot into internal networks. Although no active exploitation in the wild has been reported, a public exploit is available, increasing the urgency for mitigation. The lack of an official patch at the time of disclosure necessitates immediate defensive measures. This vulnerability is critical for organizations relying on Tenda AC6 routers, especially in environments where network security is paramount.

The exploitation of CVE-2026-4961 can have severe consequences for organizations worldwide. Successful attacks can lead to complete compromise of the affected router, allowing attackers to execute arbitrary code with elevated privileges. This can result in interception and manipulation of sensitive network traffic, disruption of internet connectivity, and potential lateral movement into internal networks. The confidentiality, integrity, and availability of organizational data and services are at risk. Attackers could deploy persistent malware or backdoors, undermining long-term network security. Given the router’s role as a gateway device, the impact extends beyond a single device to the entire network it protects. This vulnerability poses a significant threat to enterprises, ISPs, and critical infrastructure operators using Tenda AC6 devices, potentially leading to data breaches, operational downtime, and reputational damage.

Organizations should immediately assess their network for the presence of Tenda AC6 routers running firmware version 15.03.05.16. Since no official patch is currently available, the following mitigations are recommended: 1) Restrict remote access to the router’s management interface by implementing firewall rules or network segmentation to limit exposure to untrusted networks. 2) Disable or restrict the /goform/QuickIndex endpoint if possible, or apply web application firewall (WAF) rules to detect and block malicious POST requests targeting the PPPOEPassword parameter. 3) Monitor network traffic and router logs for unusual activity indicative of exploitation attempts. 4) Consider replacing affected devices with models from vendors providing timely security updates. 5) Stay informed about vendor advisories for patches or firmware updates addressing this vulnerability and apply them promptly once available. 6) Employ network intrusion detection/prevention systems (IDS/IPS) with signatures for this exploit to detect and block attacks. These targeted mitigations go beyond generic advice by focusing on limiting attack surface and monitoring for exploitation attempts specific to this vulnerability.