CVE-2020-7748 in @tsed
Summary
by MITRE • 10/20/2020
This affects the package @tsed/core before 5.65.7. This vulnerability relates to the deepExtend function which is used as part of the utils directory. Depending on if user input is provided, an attacker can overwrite and pollute the object prototype of a program.
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Analysis
by VulDB Data Team • 11/21/2020
The vulnerability identified as CVE-2020-7748 resides within the @tsed/core package, specifically affecting versions prior to 5.65.7. This issue manifests through the deepExtend function located within the utils directory, representing a critical prototype pollution vulnerability that can have far-reaching implications for applications utilizing this dependency. The flaw stems from inadequate input validation and sanitization mechanisms within the deepExtend utility function, which is designed to merge nested objects recursively but fails to properly handle user-provided data during the merging process.
The technical nature of this vulnerability aligns with CWE-471, which describes the weakness of "Modification of Assumed-Immutable Data" and is closely related to prototype pollution attacks that fall under the ATT&CK technique T1190. The deepExtend function processes user input without proper safeguards, allowing an attacker to inject malicious properties into the Object prototype itself. When user-controlled data is passed through this function, it can manipulate the prototype chain of objects, enabling attackers to pollute the object prototype with malicious properties that persist across the entire application runtime. This occurs because the function does not adequately validate or sanitize the keys of incoming objects, particularly when dealing with nested structures that might contain special property names.
The operational impact of this vulnerability is significant as it can lead to various security consequences including but not limited to denial of service attacks, arbitrary code execution, and privilege escalation. When an attacker successfully pollutes the prototype, they can manipulate how objects behave throughout the application, potentially causing unexpected behavior in critical system functions. Applications that rely on object property checking, serialization, or inheritance patterns become vulnerable to exploitation since the prototype pollution can affect core JavaScript functionality. The vulnerability is particularly dangerous because it can be exploited through various attack vectors including API endpoints, configuration files, or any input mechanism that passes data through the deepExtend function.
Mitigation strategies for CVE-2020-7748 should focus on immediate remediation by upgrading to @tsed/core version 5.65.7 or later, which contains the patched deepExtend function with proper input validation. Organizations should also implement comprehensive input sanitization measures, particularly for any user-provided data that might eventually pass through object merging utilities. Additional defensive measures include implementing prototype pollution detection mechanisms, using secure coding practices that avoid direct property assignment to objects, and employing runtime monitoring solutions that can detect anomalous prototype modifications. The vulnerability underscores the importance of proper object handling in JavaScript applications and highlights the need for robust security testing of utility functions that manipulate object structures. Security teams should also consider implementing automated dependency scanning tools to identify and remediate similar vulnerabilities across their software supply chain, as prototype pollution remains a persistent threat in modern web applications.