The vulnerability CVE-2025-66565 affects the gofiber utils library, a set of common utility functions used in Fiber, a popular Go web framework. In versions 2.0.0-rc.3 and below, two functions that generate UUIDs rely on the system's cryptographic random number generator (crypto/rand). When crypto/rand.Read() fails, these functions do not properly handle the error and instead silently fallback to returning predictable UUID values, including the zero UUID (00000000-0000-0000-0000-000000000000). This fallback behavior violates secure coding practices (CWE-252: unchecked return value) and results in weak randomness (CWE-331) and predictable UUIDs (CWE-338). Since UUIDs are often used for security-critical operations such as session identifiers, tokens, or unique keys, predictable UUIDs can lead to impersonation, session fixation, or other attacks compromising confidentiality and integrity. The vulnerability is remotely exploitable without authentication or user interaction, making it highly severe. The issue was fixed in version 2.0.0-rc.4 by properly handling crypto/rand failures and avoiding fallback to predictable UUIDs. No public exploits have been reported yet, but the critical CVSS score of 9.3 reflects the high risk posed by this vulnerability.

For European organizations, this vulnerability poses a significant risk to web applications built using the Fiber framework with affected versions of gofiber utils. Attackers could exploit predictable UUID generation to impersonate users, hijack sessions, or bypass security controls relying on UUID uniqueness and randomness. This can lead to data breaches, unauthorized access, and potential regulatory non-compliance under GDPR due to compromised confidentiality and integrity of personal data. The silent fallback to predictable UUIDs makes detection difficult, increasing the risk of undetected exploitation. Industries with high reliance on Fiber-based applications, such as fintech, e-commerce, and public sector services, are particularly vulnerable. The vulnerability's remote exploitability and lack of required privileges amplify its threat. Organizations may face reputational damage and financial losses if exploited.

European organizations should immediately upgrade all gofiber utils dependencies to version 2.0.0-rc.4 or later to ensure the vulnerability is patched. Conduct a thorough code audit to identify all uses of UUID generation in security-critical contexts and verify that no fallback to predictable UUIDs occurs. Implement additional runtime checks to detect failures in crypto/rand and log such events for early warning. Where feasible, replace UUID-based security tokens with cryptographically secure random values generated by well-maintained libraries. Employ defense-in-depth by enforcing strict session management, multi-factor authentication, and anomaly detection to mitigate potential exploitation. Regularly monitor Fiber framework and gofiber utils releases for further security updates. Educate developers on proper error handling and secure random number generation best practices to prevent similar issues.