CVE-2020-8136 in fastify-multipart
Summary
by MITRE
Prototype pollution vulnerability in fastify-multipart < 1.0.5 allows an attacker to crash fastify applications parsing multipart requests by sending a specially crafted request.
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Analysis
by VulDB Data Team • 04/18/2024
The CVE-2020-8136 vulnerability represents a critical prototype pollution flaw affecting the fastify-multipart library version 1.0.4 and earlier. This vulnerability specifically targets the multipart request parsing functionality within fastify applications, creating a dangerous condition where malicious actors can manipulate object prototypes through crafted HTTP requests. The issue arises from inadequate input validation and sanitization mechanisms within the library's handling of multipart form data, particularly when processing nested field names that contain special characters or sequences.
The technical exploitation of this vulnerability occurs when an attacker sends a multipart request containing specially crafted field names that contain prototype pollution indicators such as _proto_ or constructor. When the fastify-multipart library processes these requests, it fails to properly sanitize the incoming data, allowing the malicious payload to modify the Object.prototype directly. This prototype pollution can then be leveraged by attackers to manipulate the behavior of the application at runtime, potentially leading to denial of service conditions or more severe security implications depending on how the application utilizes the parsed data.
The operational impact of CVE-2020-8136 extends beyond simple application crashes, as prototype pollution vulnerabilities can create cascading effects throughout the application's execution environment. Fastify applications that rely on fastify-multipart for handling file uploads or form submissions become vulnerable to this attack vector, with the potential for attackers to disrupt service availability or manipulate application logic. The vulnerability is particularly concerning because it can be exploited through legitimate multipart request parsing operations, making detection difficult and the attack surface broad.
This vulnerability aligns with CWE-471, which specifically addresses the weakness of "Modification of Assumed-Immutable Data" in the context of prototype pollution attacks. The flaw demonstrates a clear failure in input validation and sanitization practices, as outlined in the OWASP Top 10 security principles. From an ATT&CK framework perspective, this vulnerability maps to T1211 - Exploitation for Defense Evasion and T1499 - Endpoint Termination, as attackers can leverage it to crash services and disrupt availability. The attack requires minimal sophistication and can be automated, making it particularly dangerous in environments where fastify applications process untrusted multipart data.
Organizations should immediately upgrade to fastify-multipart version 1.0.5 or later, which includes proper input sanitization and prototype pollution prevention mechanisms. Additionally, implementing proper request validation, rate limiting, and monitoring for unusual multipart request patterns can help detect and prevent exploitation attempts. Network segmentation and application-level firewalls should be configured to restrict access to multipart endpoints where possible. Security teams should also conduct thorough code reviews to identify any other potential prototype pollution vulnerabilities in their application's dependency tree, as similar issues may exist in other libraries handling user-provided data. The fix implemented in version 1.0.5 typically involves comprehensive sanitization of field names and proper handling of special characters in multipart form data to prevent prototype manipulation attacks.