CVE-2025-7673 is a critical buffer overflow vulnerability identified in the URL parser component of the zhttpd web server embedded within the Zyxel VMG8825-T50K firmware versions prior to V5.50(ABOM.5)C0. This vulnerability arises due to improper bounds checking during buffer copy operations (CWE-120), allowing an attacker to overflow the buffer by sending a specially crafted HTTP request containing an excessively long or malformed URL. Because the vulnerability exists in the URL parsing logic, it can be triggered remotely without any authentication or user interaction. Successful exploitation can lead to denial-of-service (DoS) conditions by crashing the web server or, more critically, arbitrary code execution with the privileges of the web server process. Given the CVSS v3.1 base score of 9.8, the vulnerability is rated as critical, reflecting its high impact on confidentiality, integrity, and availability, combined with ease of exploitation over the network. The vulnerability affects Zyxel VMG8825-T50K devices running firmware versions earlier than V5.50(ABOM.5)C0, which are commonly deployed as residential or small office gateway routers. Although no known exploits have been reported in the wild yet, the severity and ease of exploitation make it a high-priority issue for affected users and organizations. The lack of available patches at the time of reporting necessitates immediate mitigation efforts to reduce exposure.

For European organizations, the impact of this vulnerability can be significant, especially for enterprises and ISPs relying on Zyxel VMG8825-T50K devices for network connectivity and security. Exploitation could lead to network outages due to DoS, disrupting business operations and communications. More severe consequences include potential remote code execution, which could allow attackers to gain control over the affected device, pivot into internal networks, intercept or manipulate sensitive data, and launch further attacks. This is particularly concerning for organizations handling sensitive personal data under GDPR, as a breach could result in regulatory penalties and reputational damage. Small and medium-sized enterprises (SMEs) and home office setups using these routers may be especially vulnerable due to limited IT security resources and delayed patching. Additionally, critical infrastructure sectors that utilize these devices for connectivity could face operational disruptions or targeted attacks. The vulnerability's network-exploitable nature means it could be leveraged by remote attackers without any prior access, increasing the risk of widespread exploitation if weaponized.

1. Immediate firmware upgrade: Organizations should prioritize updating affected Zyxel VMG8825-T50K devices to firmware version V5.50(ABOM.5)C0 or later as soon as the patch becomes available. 2. Network segmentation: Isolate vulnerable devices from critical internal networks to limit potential lateral movement in case of compromise. 3. Access restrictions: Restrict remote management interfaces and HTTP access to trusted IP addresses only, using firewall rules or VPNs. 4. Intrusion detection: Deploy network intrusion detection systems (NIDS) with signatures or anomaly detection tuned to identify unusual HTTP requests targeting the zhttpd server. 5. Monitoring and logging: Enable detailed logging on affected devices and monitor for unusual traffic patterns or repeated malformed HTTP requests. 6. Temporary mitigations: If patching is delayed, consider disabling the web management interface or replacing vulnerable devices with alternative hardware until a fix is applied. 7. Vendor engagement: Maintain communication with Zyxel for updates and advisories regarding this vulnerability and any emerging exploits. 8. Incident response readiness: Prepare incident response plans to quickly address potential exploitation attempts, including isolating affected devices and forensic analysis.