CVE-2025-57638 is a high-severity buffer overflow vulnerability identified in the Tenda AC9 router firmware version 1.0. The vulnerability arises from improper handling of the user-supplied 'sys.vendor' configuration value, which can lead to a buffer overflow condition. Buffer overflow vulnerabilities occur when a program writes more data to a buffer than it can hold, potentially overwriting adjacent memory. In this case, the vulnerability allows an unauthenticated remote attacker to send a specially crafted input to the router's configuration interface, causing the overflow without requiring any user interaction or prior authentication. The CVSS v3.1 base score of 7.5 reflects the network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), unchanged scope (S:U), no impact on confidentiality or integrity (C:N/I:N), but a high impact on availability (A:H). This means exploitation could result in denial of service (DoS) conditions, such as router crashes or reboots, disrupting network connectivity. The vulnerability is categorized under CWE-122 (Heap-based Buffer Overflow), indicating that the overflow occurs in the heap memory area, which can sometimes be leveraged for more advanced exploitation like remote code execution, although no such exploits are currently known in the wild. No patches or fixes have been published yet, and the affected versions are not explicitly detailed beyond version 1.0. The vulnerability was reserved in August 2025 and published in September 2025, indicating recent discovery.

For European organizations, the impact of this vulnerability primarily involves potential disruption of network infrastructure due to router unavailability. The Tenda AC9 is a consumer-grade wireless router, but it is also used in small offices and home office (SOHO) environments, which are common in European SMEs. A successful exploit could cause denial of service, interrupting internet access and internal network communications. While the vulnerability does not directly compromise confidentiality or integrity, the loss of availability can hinder business operations, remote work, and critical communications. Additionally, if attackers leverage this vulnerability as a foothold, they might attempt lateral movement within networks, although this is speculative given current information. The lack of authentication and user interaction requirements increases the risk, as attackers can remotely trigger the overflow without user awareness. European organizations relying on Tenda AC9 routers should be aware of the potential for targeted attacks aiming to disrupt services, especially in sectors where network uptime is critical, such as healthcare, finance, and public administration.

Given the absence of an official patch, European organizations should implement immediate compensating controls. First, isolate Tenda AC9 routers from direct exposure to the internet by placing them behind firewalls or using network segmentation to limit access to the router's management interface. Disable remote management features if enabled, to prevent external attackers from reaching the vulnerable configuration interface. Monitor network traffic for unusual patterns or repeated malformed packets targeting the router. Organizations should also consider replacing Tenda AC9 devices with alternative routers from vendors with a stronger security track record if feasible. Regularly check for firmware updates from Tenda and apply patches promptly once available. Employ network intrusion detection systems (NIDS) capable of detecting exploitation attempts targeting buffer overflow vulnerabilities. Finally, maintain up-to-date asset inventories to quickly identify affected devices and prioritize remediation efforts.