CVE-2021-25943 in 101
Summary
by MITRE • 05/15/2021
Prototype pollution vulnerability in '101' versions 1.0.0 through 1.6.3 allows an attacker to cause a denial of service and may lead to remote code execution.
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Analysis
by VulDB Data Team • 05/01/2025
The vulnerability identified as CVE-2021-25943 represents a critical prototype pollution flaw affecting the '101' library versions 1.0.0 through 1.6.3. This vulnerability stems from improper handling of object prototypes during runtime execution, creating a pathway for malicious actors to manipulate the prototype chain of JavaScript objects. The issue manifests when the library processes user-supplied input without adequate validation, allowing attackers to inject malicious properties into the Object.prototype object itself. This fundamental flaw enables attackers to modify the behavior of all objects that inherit from the prototype, potentially leading to severe security implications across the entire application runtime environment.
The technical exploitation of this prototype pollution vulnerability follows a specific attack pattern that aligns with CWE-471, which classifies the issue as improper handling of prototype pollution. When an attacker supplies malicious input that gets processed by the vulnerable library, they can inject properties into the prototype chain that persist across all object instances. This occurs because the library fails to sanitize input parameters before incorporating them into object structures. The vulnerability particularly affects applications that rely on the 101 library for data processing or object manipulation, where user input flows through the library's functions without proper sanitization. The attack vector typically involves sending specially crafted JSON or object data that triggers the prototype pollution during deserialization or object merging operations.
The operational impact of CVE-2021-25943 extends beyond simple denial of service conditions to encompass potential remote code execution capabilities, making it a severe threat to affected systems. While the primary consequence is denial of service through prototype manipulation that can crash applications or cause unexpected behavior, the secondary impact includes the possibility of remote code execution through exploitation of the prototype pollution. This occurs when the polluted prototype properties interact with other vulnerable components in the application stack, potentially enabling attackers to execute arbitrary code on the target system. The vulnerability affects both server-side and client-side applications that utilize the affected library versions, creating widespread exposure across different deployment environments and threat surfaces.
Organizations affected by this vulnerability should implement immediate mitigations to protect their systems from exploitation attempts. The primary recommendation involves updating to the latest available version of the 101 library where the prototype pollution vulnerability has been patched. Additionally, input validation and sanitization should be strengthened at all application boundaries where user data enters the system, particularly when processing JSON or object data structures. Implementing Content Security Policy headers and using secure coding practices that prevent prototype manipulation can provide additional defense layers. The vulnerability also aligns with ATT&CK technique T1059.007 for remote code execution and T1499.004 for denial of service, making it a multi-faceted threat requiring comprehensive defensive measures. Security monitoring should be enhanced to detect anomalous object creation patterns or unexpected prototype modifications that could indicate exploitation attempts.