CVE-2024-21891 is a high-severity vulnerability affecting Node.js versions 4.0 through 21.0, specifically targeting the experimental permission model introduced in Node.js 20 and 21. The core issue arises from the way Node.js relies on built-in utility functions to normalize file system paths passed to the node:fs module functions. These utility functions can be overwritten by user-defined implementations, which enables an attacker to perform a path traversal attack. This attack bypasses the filesystem permission model, potentially allowing unauthorized access to files outside the intended directory scope. The vulnerability is classified under CWE-22 (Improper Limitation of a Pathname to a Restricted Directory), indicating a failure to properly sanitize or validate file paths. Exploitation requires local privileges (AV:L - Attack Vector: Local), low attack complexity (AC:L), and low privileges (PR:L), but does require user interaction (UI:R). The scope is changed (S:C), meaning the vulnerability affects resources beyond the initially vulnerable component. The impact on confidentiality and integrity is high (C:H/I:H), but availability is not affected (A:N). No known exploits are currently reported in the wild, and no official patches have been linked yet. The vulnerability is particularly relevant for environments using the experimental permission model, which is not yet widely adopted but may be in use in cutting-edge or development environments. Given the broad range of affected Node.js versions, many applications and services that depend on Node.js could be indirectly impacted if they adopt this experimental feature or if the vulnerability is leveraged in development or staging environments.

For European organizations, the impact of CVE-2024-21891 can be significant, especially for those relying on Node.js in development, production, or experimental environments. The vulnerability allows an attacker with local access and limited privileges to bypass filesystem permission controls, potentially exposing sensitive data or modifying critical files. This can lead to data breaches, intellectual property theft, or unauthorized code execution, undermining the integrity of applications. Organizations in sectors such as finance, healthcare, telecommunications, and critical infrastructure, which often use Node.js for backend services, could face compliance violations under GDPR if personal data is exposed. The experimental nature of the permission model means that many production systems may not yet be vulnerable, but early adopters or developers testing new features are at risk. Additionally, the path traversal nature of the attack could facilitate lateral movement within compromised systems, increasing the threat surface. The lack of known exploits in the wild suggests limited immediate risk, but the high CVSS score and potential for privilege escalation warrant proactive measures.

1. Avoid using the experimental permission model in Node.js 20 and 21 in production environments until a secure patch is released. 2. Monitor Node.js official channels and security advisories for patches addressing CVE-2024-21891 and apply updates promptly once available. 3. Implement strict code review and auditing processes to detect any user-defined overrides of built-in utility functions related to path normalization. 4. Employ runtime application self-protection (RASP) or host-based intrusion detection systems (HIDS) to detect anomalous filesystem access patterns indicative of path traversal attempts. 5. Limit local user privileges and enforce the principle of least privilege to reduce the risk of exploitation by low-privileged users. 6. Use containerization or sandboxing to isolate Node.js applications, minimizing the impact of potential permission bypasses. 7. Conduct penetration testing focusing on path traversal and permission model bypass scenarios, especially in environments experimenting with the new permission model. 8. Educate developers about the risks of overriding built-in functions and the importance of secure path handling practices.