CVE-2025-55603 is a critical buffer overflow vulnerability identified in the Tenda AX3 router firmware version V16.03.12.10_CN. The flaw exists in the fromSetSysTime function, which processes the ntpServer parameter. This parameter is used to specify the Network Time Protocol (NTP) server from which the device synchronizes its system time. Due to improper bounds checking or insufficient validation of the ntpServer input, an attacker can supply a specially crafted payload that overflows the buffer allocated for this parameter. This overflow can overwrite adjacent memory, potentially allowing arbitrary code execution on the device without requiring any authentication or user interaction. The vulnerability is classified under CWE-120 (Classic Buffer Overflow), which is a well-known and dangerous class of memory corruption bugs. The CVSS v3.1 base score is 9.8, indicating a critical severity with network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), and impacts on confidentiality, integrity, and availability (C:H/I:H/A:H). Although no known exploits are currently reported in the wild, the ease of exploitation and the critical impact make this a high-risk vulnerability for affected devices. The lack of available patches at the time of publication further increases the urgency for mitigation.

For European organizations, the exploitation of this vulnerability could have severe consequences. The Tenda AX3 router is a consumer and small office/home office (SOHO) device, but it is also used in small businesses and branch offices. Successful exploitation could lead to complete compromise of the router, allowing attackers to intercept, modify, or disrupt network traffic, launch man-in-the-middle attacks, or pivot into internal networks. This could result in data breaches, loss of sensitive information, disruption of business operations, and potential lateral movement to more critical infrastructure. Given the critical nature of the vulnerability and the lack of authentication or user interaction requirements, attackers could remotely compromise devices en masse. This poses a significant risk to the confidentiality, integrity, and availability of organizational networks, especially in environments where these routers are deployed without additional network segmentation or security controls.

Immediate mitigation steps should include isolating affected Tenda AX3 devices from critical network segments and restricting inbound network access to the router's management interfaces. Network administrators should monitor network traffic for unusual NTP requests or anomalies that could indicate exploitation attempts. Since no official patches are currently available, organizations should consider temporarily replacing vulnerable devices with alternative hardware or firmware versions known to be secure. Applying strict firewall rules to block unsolicited inbound traffic targeting the router and disabling NTP synchronization from untrusted sources can reduce exposure. Additionally, organizations should implement network segmentation to limit the impact of a compromised router and deploy intrusion detection/prevention systems (IDS/IPS) tuned to detect buffer overflow attempts or unusual NTP traffic patterns. Regularly checking for vendor updates and applying firmware patches as soon as they become available is critical. Finally, organizations should conduct thorough security assessments of their network infrastructure to identify and remediate other potential vulnerabilities.