CVE-2025-11848 is a null pointer dereference vulnerability classified under CWE-476, found in the Wake-on-LAN CGI program of Zyxel VMG3625-T50B and WX3100-T0 firmware versions up to 5.50(ABPM.9.6)C0 and 5.50(ABVL.4.8)C0 respectively. This flaw arises when the software improperly handles a null pointer during processing of HTTP requests related to Wake-on-LAN functionality. An authenticated attacker with administrator privileges can send a specially crafted HTTP request that causes the device firmware to dereference a null pointer, leading to a denial-of-service condition by crashing or freezing the device. The vulnerability does not expose sensitive data or allow unauthorized code execution but disrupts device availability. The CVSS v3.1 base score is 4.9, with attack vector network, low attack complexity, high privileges required, no user interaction, unchanged scope, and impact limited to availability. No public patches or exploits are currently known, but the vulnerability is publicly disclosed and assigned a CVE identifier. The affected Zyxel devices are commonly used as residential or small office gateways, often deployed in environments where uptime is critical. The Wake-on-LAN CGI interface is typically accessible to administrators, meaning exploitation requires valid credentials or compromised admin accounts. This vulnerability highlights the importance of secure firmware development and robust input validation in embedded network devices.

The primary impact of CVE-2025-11848 is denial of service, which can cause affected Zyxel devices to crash or become unresponsive, disrupting network connectivity and services dependent on these gateways. For organizations relying on these devices for internet access, VPN termination, or network segmentation, this could result in temporary loss of network availability, impacting business operations, communications, and security monitoring. Although the vulnerability does not compromise confidentiality or integrity, the availability disruption could affect critical infrastructure, especially in environments with limited redundancy or manual recovery processes. Attackers with administrator access could leverage this vulnerability to perform targeted DoS attacks, potentially as part of a broader attack chain. The requirement for high privileges limits the attack surface to insiders or attackers who have already compromised administrative credentials, but this does not eliminate risk in environments with weak access controls or credential management. The absence of known exploits reduces immediate risk, but the public disclosure increases the likelihood of future exploitation attempts.

To mitigate CVE-2025-11848, organizations should first restrict administrative access to Zyxel devices by enforcing strong authentication mechanisms, such as multi-factor authentication and strict password policies. Network segmentation should be applied to isolate management interfaces from general user networks and the internet. Monitoring and logging of HTTP requests to the Wake-on-LAN CGI interface should be implemented to detect anomalous or malformed requests indicative of exploitation attempts. Administrators should regularly audit access logs and review device behavior for signs of instability or crashes. Until a vendor patch is released, consider disabling Wake-on-LAN functionality if not required, or limiting its exposure to trusted networks only. Firmware should be updated promptly once Zyxel releases a patch addressing this vulnerability. Additionally, organizations should implement incident response plans to quickly recover from potential DoS conditions caused by exploitation. Employing network-level protections such as intrusion detection/prevention systems (IDS/IPS) with signatures for malformed HTTP requests targeting these devices can provide additional defense.