CVE-2026-5204 is a stack-based buffer overflow vulnerability identified in the Tenda CH22 router firmware version 1.0.0.1. The flaw exists in the formWebTypeLibrary function within the /goform/webtypelibrary endpoint, which is part of the device's parameter handling mechanism. Specifically, the vulnerability is triggered by manipulating the webSiteId argument, which is not properly validated or bounded, leading to a stack buffer overflow condition. This overflow can be exploited remotely over the network without requiring authentication or user interaction, making it highly accessible to attackers. Successful exploitation can allow an attacker to execute arbitrary code with elevated privileges on the device, potentially leading to full device compromise. The vulnerability has a CVSS 4.0 base score of 8.7, reflecting high severity due to its network attack vector, lack of required privileges, and high impact on confidentiality, integrity, and availability. Although no public exploit code has been observed in the wild yet, the public disclosure increases the likelihood of future exploitation attempts. The lack of available patches at the time of disclosure further elevates the risk. This vulnerability affects the Tenda CH22 product line, which is commonly used in small office and home office environments, as well as some enterprise edge deployments.

The impact of CVE-2026-5204 is significant for organizations using Tenda CH22 devices. Exploitation can lead to complete compromise of the device, enabling attackers to execute arbitrary code, potentially install persistent malware, intercept or manipulate network traffic, and disrupt network availability. This can result in loss of confidentiality of sensitive data traversing the device, integrity violations through unauthorized configuration changes or traffic manipulation, and denial of service conditions. Given the device's role as a network edge router, compromise can serve as a foothold for lateral movement into internal networks, increasing the overall risk exposure. Organizations relying on these devices for critical connectivity or security functions face elevated risks of operational disruption and data breaches. The remote and unauthenticated nature of the exploit vector makes it particularly dangerous, as attackers can scan and target vulnerable devices at scale without prior access.

To mitigate CVE-2026-5204, organizations should immediately identify all Tenda CH22 devices running firmware version 1.0.0.1 and restrict their network exposure. Until an official patch is released, apply the following specific measures: 1) Isolate affected devices behind firewalls or VPNs to limit access to trusted networks only. 2) Disable remote management interfaces or restrict them to known IP addresses. 3) Monitor network traffic for unusual requests targeting /goform/webtypelibrary or suspicious webSiteId parameter usage. 4) Employ intrusion detection/prevention systems (IDS/IPS) with signatures for buffer overflow attempts against Tenda devices. 5) Regularly audit device firmware versions and vendor advisories for patch availability and apply updates promptly once released. 6) Consider network segmentation to limit the impact of a compromised device. 7) Educate network administrators on the risks and signs of exploitation attempts. These targeted actions go beyond generic advice by focusing on limiting attack surface and early detection specific to this vulnerability.