CVE-2025-66630 is a vulnerability in the GoFiber web framework, specifically versions before 2.52.11, that stems from the use of a cryptographically weak pseudo-random number generator (PRNG) when generating UUIDs. Fiber relies on Go's crypto/rand package to produce secure random values for UUIDv4 generation, which are widely used in Fiber's middleware components such as session management, CSRF tokens, rate limiting, and request ID generation. However, in Go versions prior to 1.24, the crypto/rand implementation can fail to provide secure randomness and return an error. Fiber's UUID functions do not return or handle this error, causing the application to unknowingly use predictable or repeated UUIDs with low entropy. This undermines the security guarantees of middleware relying on these UUIDs, potentially allowing attackers to predict session identifiers, bypass CSRF protections, evade rate limits, or manipulate request tracking. The vulnerability is classified under CWE-338 (Use of Cryptographically Weak PRNG). It has a CVSS 4.0 score of 9.2, indicating critical severity with network attack vector, high impact on confidentiality and integrity, and no required privileges or user interaction. The issue is fixed in Fiber version 2.52.11, which properly handles errors from crypto/rand and ensures secure UUID generation. No known exploits have been reported yet, but the widespread use of Fiber and its middleware in Go web applications makes this a significant threat vector.

For European organizations, this vulnerability poses a critical risk to web applications built on the GoFiber framework using affected versions and running on Go versions prior to 1.24. The predictable UUIDs can lead to session hijacking, bypass of CSRF protections, manipulation of rate limiting, and request forgery, potentially resulting in unauthorized access, data leakage, and service disruption. Organizations in sectors with high security requirements such as finance, healthcare, government, and e-commerce are particularly at risk. The impact is exacerbated by the default use of vulnerable UUID generation in many Fiber middleware components, meaning even applications without explicit UUID usage may be affected. Exploitation could compromise user data confidentiality and integrity, damage trust, and lead to regulatory non-compliance under GDPR and other data protection laws. The critical CVSS score reflects the ease of remote exploitation without authentication or user interaction, increasing the urgency for mitigation.

European organizations should immediately upgrade all GoFiber dependencies to version 2.52.11 or later to ensure the vulnerability is patched. Additionally, they should verify that their Go runtime environment is version 1.24 or newer, as earlier versions have the underlying crypto/rand issue. Application developers must audit their code and middleware usage to confirm that UUID generation is secure and that no fallback to weak randomness occurs. Implementing runtime monitoring for unusual session or token reuse patterns can help detect exploitation attempts. Security teams should also review and strengthen session management, CSRF protections, and rate limiting configurations to reduce reliance on UUIDs alone. Where possible, consider integrating additional entropy sources or alternative secure random number generators. Finally, conduct penetration testing focused on session fixation and CSRF bypass scenarios to validate mitigations.