CVE-2025-63835 is a stack-based buffer overflow vulnerability identified in the Tenda AC18 router firmware version 15.03.05.05_multi. The flaw resides in the handling of the guestSsid parameter within the /goform/WifiGuestSet HTTP interface. Specifically, the router fails to properly validate the length of input data sent to this parameter, allowing an attacker to send oversized payloads that overflow the stack buffer. This overflow can lead to a denial of service condition by crashing the device, or potentially enable remote code execution if the attacker can control the execution flow. The vulnerability is exploitable remotely without requiring authentication or user interaction, but the attack vector is limited to adjacent network access, meaning the attacker must be on the same local network or connected via a compromised device. The CVSS v3.1 base score is 6.5, indicating a medium severity primarily due to the high impact on availability (device crash) but no direct impact on confidentiality or integrity. No patches or official fixes have been released as of the publication date, and there are no known exploits in the wild. The vulnerability is classified under CWE-121 (stack-based buffer overflow), a common and dangerous class of memory corruption bugs. Given the widespread use of Tenda AC18 routers in consumer and small business environments, this vulnerability poses a risk for denial of service attacks and potentially more severe compromises if exploited for code execution.

For European organizations, the primary impact of CVE-2025-63835 is the potential for denial of service attacks against Tenda AC18 routers, which could disrupt internet connectivity and internal network access. This is particularly critical for small and medium enterprises (SMEs) and home office setups that rely on these routers for network access and may lack redundant infrastructure. While the vulnerability does not directly compromise confidentiality or integrity, a successful remote code execution exploit could allow attackers to gain control over the router, leading to network reconnaissance, traffic interception, or pivoting attacks within the network. Disruption of network availability could impact business operations, remote work capabilities, and access to cloud services. The lack of authentication requirement lowers the barrier for exploitation, increasing risk in environments where network segmentation is weak. The absence of patches means organizations must rely on interim mitigations, increasing operational risk until a fix is available.

1. Immediately segment networks to isolate Tenda AC18 routers from critical systems and sensitive data to limit attack surface. 2. Disable the guest Wi-Fi feature if it is not in use, as the vulnerability resides in the guestSsid parameter. 3. Implement strict access controls on the local network to prevent unauthorized devices from connecting and attempting exploitation. 4. Monitor router logs and network traffic for unusual requests to the /goform/WifiGuestSet interface or signs of device instability and crashes. 5. Where possible, replace vulnerable Tenda AC18 routers with alternative devices from vendors with timely security updates. 6. Apply network-level protections such as intrusion detection/prevention systems (IDS/IPS) to detect and block attempts to exploit this vulnerability. 7. Stay alert for official patches or firmware updates from Tenda and apply them promptly once available. 8. Educate users about the risks of connecting unknown devices to the network and enforce strong network access policies.