CVE-2026-5156 is a stack-based buffer overflow vulnerability identified in the Tenda CH22 router firmware version 1.0.0.1. The flaw resides in the formQuickIndex function within the /goform/QuickIndex endpoint, part of the parameter handling mechanism. Specifically, the vulnerability arises from improper validation and handling of the mit_linktype argument, which can be manipulated by a remote attacker to overflow the stack buffer. This overflow can corrupt the stack, potentially allowing an attacker to execute arbitrary code, crash the device, or cause denial of service. The vulnerability is remotely exploitable without requiring authentication or user interaction, increasing its severity and ease of exploitation. The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P) reflects network attack vector, low attack complexity, no privileges or user interaction needed, and high impact on confidentiality, integrity, and availability. Although no known exploits are currently active in the wild, the public disclosure of exploit details raises the likelihood of future attacks. The affected product, Tenda CH22, is a consumer-grade router commonly used in various regions, making this vulnerability a significant threat to home and small business networks relying on this device.

The impact of CVE-2026-5156 is substantial for organizations and individuals using the Tenda CH22 router. Successful exploitation can lead to remote code execution, allowing attackers to take full control of the device. This can result in interception or manipulation of network traffic, deployment of malware, pivoting to internal networks, or complete denial of service. The compromise of network infrastructure devices like routers can undermine the confidentiality, integrity, and availability of connected systems and data. For enterprises and service providers, this could lead to data breaches, service outages, and reputational damage. Given the router's role as a network gateway, exploitation could facilitate broader attacks on internal networks. The absence of authentication and user interaction requirements lowers the barrier for attackers, increasing the risk of widespread exploitation, especially if automated scanning and exploitation tools emerge.

To mitigate CVE-2026-5156, organizations should immediately check for firmware updates from Tenda addressing this vulnerability and apply patches as soon as they become available. In the absence of official patches, network administrators should restrict access to the router's management interfaces by implementing network segmentation and firewall rules to block unauthorized external access to the /goform/QuickIndex endpoint. Disabling remote management features or restricting them to trusted IP addresses can reduce exposure. Monitoring network traffic for unusual activity targeting the vulnerable endpoint can help detect exploitation attempts. Employing intrusion detection/prevention systems (IDS/IPS) with signatures for this vulnerability can provide additional defense. Users should also consider replacing affected devices with models that have a stronger security track record if patches are delayed. Regularly auditing and updating router firmware and configurations is critical to maintaining security.