CVE-2025-71021 identifies a stack overflow vulnerability in the Tenda AX-1806 router firmware version 1.0.0.1, specifically within the sub_65A28 function's processing of the serverName parameter. A stack overflow occurs when more data is written to a buffer located on the stack than it can hold, potentially overwriting adjacent memory and causing unpredictable behavior. In this case, the crafted request exploits improper bounds checking on the serverName input, leading to a crash of the router’s service and resulting in Denial of Service (DoS). The vulnerability is remotely exploitable without requiring authentication or user interaction, increasing its risk profile. The CVSS v3.1 base score of 7.5 reflects a high severity due to the network attack vector, low attack complexity, and the impact limited to availability (no confidentiality or integrity impact). No patches or exploits are currently publicly available, but the vulnerability is published and reserved as of early 2026. The CWE-121 classification highlights that the root cause is a classic stack-based buffer overflow, a common and well-understood software flaw. This vulnerability could be leveraged by attackers to disrupt network connectivity and services dependent on the affected router, potentially impacting business continuity.

For European organizations, the primary impact of CVE-2025-71021 is the potential for network outages caused by Denial of Service attacks targeting Tenda AX-1806 routers. This can disrupt internet connectivity, internal communications, and access to critical online services. Organizations relying on these routers for perimeter or internal network routing may experience downtime affecting operational continuity. The lack of confidentiality or integrity impact reduces risks related to data breaches but does not diminish the operational risks. Critical infrastructure sectors such as finance, healthcare, and government agencies could face significant disruptions if their networks use vulnerable devices. Additionally, small and medium enterprises (SMEs) that deploy consumer-grade or low-cost networking equipment like Tenda routers may be particularly exposed. The absence of known exploits in the wild currently limits immediate threat but does not preclude future exploitation, especially as proof-of-concept code or automated scanning tools emerge. The vulnerability's ease of exploitation without authentication increases the likelihood of opportunistic attacks, especially in environments with exposed management interfaces or weak network segmentation.

1. Monitor Tenda’s official channels for firmware updates addressing CVE-2025-71021 and apply patches promptly once released. 2. Restrict access to router management interfaces by implementing network segmentation and firewall rules to limit exposure to trusted IP addresses only. 3. Disable remote management features if not required to reduce the attack surface. 4. Employ intrusion detection/prevention systems (IDS/IPS) to detect anomalous or malformed requests targeting the serverName parameter or unusual traffic patterns to the router. 5. Conduct regular network device audits to inventory and identify vulnerable Tenda AX-1806 devices within the environment. 6. Consider replacing vulnerable routers with models from vendors with stronger security track records if patching is delayed or unavailable. 7. Educate IT staff on recognizing signs of DoS attacks and establishing incident response procedures to quickly isolate affected devices. 8. Implement network-level rate limiting to mitigate the impact of potential flooding attacks exploiting this vulnerability.