CVE-2025-55740 is a configuration vulnerability in Anipaleja's nginx-defender, a high-performance Web Application Firewall (WAF) and threat detection system designed for modern web infrastructures. The vulnerability arises from the use of default credentials embedded in example configuration files (config.yaml and docker-compose.yml), specifically the default_password set to "change_me_please" and GF_SECURITY_ADMIN_PASSWORD set to "admin123". If these default credentials are not changed by administrators before deployment, an attacker with network access can gain unauthorized administrative control over the nginx-defender system. This administrative access allows the attacker to bypass the WAF's security protections, potentially enabling them to manipulate firewall rules, disable threat detection, or otherwise compromise the security posture of the protected web applications. The vulnerability affects all versions of nginx-defender prior to 1.5.0, with the issue resolved in version 1.5.0 and later. The CVSS v3.1 base score is 6.5, indicating a medium severity level. The vector (AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N) shows that the vulnerability is remotely exploitable over the network without any privileges or user interaction, impacting confidentiality and integrity but not availability. There are no known exploits in the wild at this time. The root cause is classified under CWE-1392, which relates to the use of default credentials, a common misconfiguration leading to unauthorized access.

For European organizations, the impact of this vulnerability can be significant, especially for those relying on nginx-defender as a critical component of their web security infrastructure. Unauthorized administrative access to the WAF can lead to the disabling or modification of security rules, allowing attackers to bypass protections and potentially compromise sensitive data or web services. This undermines the confidentiality and integrity of web applications and data processed by these systems. Given that the vulnerability does not affect availability directly, denial-of-service is less of a concern, but the stealthy nature of administrative compromise can facilitate prolonged undetected attacks. Organizations in sectors with strict data protection regulations, such as finance, healthcare, and government, face increased risk of regulatory non-compliance and reputational damage if this vulnerability is exploited. Additionally, since exploitation requires only network access and no user interaction, attackers within the same network segment or those who can reach the WAF over the internet (if exposed) can exploit this vulnerability, increasing the attack surface.

To mitigate this vulnerability effectively, organizations should: 1) Immediately upgrade all nginx-defender deployments to version 1.5.0 or later, where the default credential issue is resolved. 2) Conduct a thorough audit of existing nginx-defender configurations to identify any instances where default credentials remain in use. 3) Enforce strict configuration management policies that mandate changing all default passwords before deployment, including in example or template files. 4) Implement network segmentation and access controls to restrict network access to the WAF management interfaces only to trusted administrative hosts and personnel. 5) Enable and monitor detailed logging and alerting on administrative access to detect any unauthorized attempts promptly. 6) Consider integrating multi-factor authentication (MFA) for administrative access if supported by the product or via external access control mechanisms. 7) Educate system administrators and DevOps teams about the risks of default credentials and the importance of secure configuration practices. 8) Regularly review and update security policies to include checks for default credentials in all deployed software components.