CVE-2025-11847 is a null pointer dereference vulnerability classified under CWE-476 found in the IP settings 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. The flaw arises when the CGI program improperly handles certain crafted HTTP requests, leading to a null pointer dereference that causes the device to crash or reboot, resulting in a denial-of-service (DoS) condition. Exploitation requires the attacker to be authenticated with administrator-level privileges, as the vulnerability is triggered via the device’s web interface. The CVSS v3.1 base score is 4.9, reflecting a medium severity due to the requirement for high privileges and the impact being limited to availability disruption without affecting confidentiality or integrity. No user interaction is needed beyond authentication, and no known exploits have been reported in the wild. The vulnerability affects network availability by potentially causing device downtime, which can interrupt internet or intranet connectivity for users relying on these devices. The absence of patches at the time of disclosure means organizations must rely on access controls and monitoring until updates are released. This vulnerability highlights the importance of secure firmware development and robust input validation in embedded device web interfaces.

The primary impact of CVE-2025-11847 is denial-of-service, which can disrupt network connectivity for organizations using affected Zyxel VMG3625-T50B and WX3100-T0 devices. This can lead to operational downtime, reduced productivity, and potential loss of business continuity, especially in environments where these devices serve as critical network gateways or access points. Since exploitation requires administrator privileges, the risk is somewhat mitigated but remains significant if credentials are compromised or insiders act maliciously. The lack of confidentiality or integrity impact means data breaches or unauthorized data modification are not direct concerns from this vulnerability. However, repeated or targeted DoS attacks could degrade trust in network reliability and increase operational costs due to troubleshooting and recovery efforts. Organizations with large deployments of these devices or those in sectors requiring high network availability (e.g., ISPs, enterprises, government agencies) face greater risk. The absence of known exploits reduces immediate threat but does not eliminate future exploitation potential once details become widely known.

1. Restrict administrative access to Zyxel VMG3625-T50B and WX3100-T0 devices to trusted personnel only, using strong authentication mechanisms and network segmentation to limit exposure. 2. Monitor device logs and network traffic for unusual HTTP requests targeting the IP settings CGI interface to detect potential exploitation attempts. 3. Implement strict access control lists (ACLs) on management interfaces to allow only authorized IP addresses to connect. 4. Regularly audit and rotate administrator credentials to reduce the risk of credential compromise. 5. Stay informed on Zyxel’s security advisories and apply firmware updates promptly once patches addressing CVE-2025-11847 are released. 6. Consider deploying network-level DoS protection mechanisms to mitigate impact if exploitation occurs. 7. Conduct penetration testing and vulnerability assessments focused on device management interfaces to identify and remediate similar issues proactively. These steps go beyond generic advice by emphasizing proactive monitoring, access restrictions, and credential hygiene tailored to the nature of this vulnerability.