CVE-2023-39332 in Node.js
Summary
by MITRE • 10/25/2023
Various `node:fs` functions allow specifying paths as either strings or `Uint8Array` objects. In Node.js environments, the `Buffer` class extends the `Uint8Array` class. Node.js prevents path traversal through strings (see CVE-2023-30584) and `Buffer` objects (see CVE-2023-32004), but not through non-`Buffer` `Uint8Array` objects. This is distinct from CVE-2023-32004 ([report 2038134](https://hackerone.com/reports/2038134)), which only referred to `Buffer` objects. However, the vulnerability follows the same pattern using `Uint8Array` instead of `Buffer`. Impacts: This vulnerability affects all users using the experimental permission model in Node.js 20. Please note that at the time this CVE was issued, the permission model is an experimental feature of Node.js.
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Analysis
by VulDB Data Team • 02/14/2025
The vulnerability described in CVE-2023-39332 represents a critical security flaw in Node.js's file system handling mechanisms that specifically targets the experimental permission model introduced in Node.js 20. This issue exploits a gap in path validation logic where the system properly sanitizes path traversal attempts when using strings or Buffer objects, but fails to apply the same protections to non-Buffer Uint8Array objects. The vulnerability operates at the intersection of multiple security controls and demonstrates how seemingly minor implementation differences can create significant attack vectors. The flaw is particularly concerning because it affects Node.js versions where the permission model is still experimental, meaning users may not be fully aware of the security implications or have adequate protection mechanisms in place. The vulnerability's existence stems from the inconsistent application of path traversal protections across different data types that can represent file paths within Node.js's file system APIs.
The technical implementation of this vulnerability involves the node:fs module's handling of path resolution where string-based paths and Buffer-based paths undergo proper sanitization to prevent directory traversal attacks, but Uint8Array objects that are not instances of Buffer class are not subject to the same validation checks. This creates a scenario where an attacker can craft malicious path data using Uint8Array objects to bypass the existing protections that were designed to address similar issues in CVE-2023-30584 and CVE-2023-32004. The underlying mechanism allows for path traversal through the filesystem by leveraging the fact that Uint8Array objects can contain path data that gets processed without the same sanitization logic applied to other object types. This discrepancy in validation logic represents a design flaw in how Node.js handles different representations of path data, creating an inconsistent security posture where some data types receive protection while others do not. The vulnerability follows the same attack pattern as previous path traversal issues but operates through a different data type pathway, making it particularly dangerous as it can bypass existing mitigation strategies.
The operational impact of this vulnerability extends beyond simple path traversal attacks to potentially allow unauthorized access to restricted file system resources when the experimental permission model is enabled. Attackers could exploit this weakness to access files outside of intended directories, read sensitive data, or potentially execute arbitrary code if combined with other vulnerabilities in the system. The vulnerability affects all users running Node.js 20 with the experimental permission model enabled, which means that environments where this feature is active are at risk regardless of other security controls. This creates a significant risk for applications that rely on Node.js's permission model for security boundaries, as the vulnerability essentially creates a bypass mechanism that can be exploited to circumvent the intended access controls. The experimental nature of the permission model also means that users may not have adequate monitoring or detection in place for this specific attack vector, making it more difficult to identify when exploitation occurs.
Mitigation strategies for this vulnerability should focus on implementing comprehensive input validation across all path representation types within Node.js file system operations. The most effective approach involves updating the Node.js runtime to include proper sanitization logic for all Uint8Array objects regardless of whether they are Buffer instances, ensuring consistent protection across all data types used for path specification. Organizations should also consider disabling the experimental permission model until a patched version is available, as this removes the attack surface entirely. Additionally, implementing proper monitoring and logging of file system operations can help detect potential exploitation attempts, while adhering to the principle of least privilege in application design can limit the damage if exploitation does occur. The vulnerability highlights the importance of comprehensive testing across all data type representations in security-critical code paths and demonstrates the need for consistent security controls regardless of the specific implementation details used to represent data within an application. This issue aligns with CWE-22 (Path Traversal) and represents a specific implementation weakness that could be addressed through proper input validation and consistent security controls across all path representation methods.