CVE-2021-3757 in immer
Summary
by MITRE • 09/02/2021
immer is vulnerable to Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
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Analysis
by VulDB Data Team • 09/09/2021
The vulnerability identified as CVE-2021-3757 affects the immer library, a popular JavaScript state management utility that enables immutable updates to JavaScript objects. This particular flaw represents a prototype pollution vulnerability that allows attackers to manipulate the prototype of JavaScript objects in unintended ways. The issue stems from how the library handles object property assignments during deep cloning operations, creating opportunities for malicious actors to modify core object prototypes. Such vulnerabilities are particularly dangerous because they can affect the fundamental behavior of JavaScript applications and potentially enable more severe exploits.
Prototype pollution occurs when an application fails to properly validate or sanitize user input that is used to set properties on object prototypes. In the context of the immer library, this vulnerability manifests when the library processes objects that contain malicious property names designed to alter prototype chains. The flaw allows attackers to inject properties into Object.prototype, which then propagates to all objects in the application that inherit from this prototype. This type of vulnerability is classified under CWE-471 as "Modification of Assumed-Immutable Data" and can be categorized as a variant of the broader prototype pollution attack pattern. The ATT&CK framework would classify this under T1059.007 for JavaScript execution and potentially T1555.003 for credential access if the pollution leads to privilege escalation.
The operational impact of this vulnerability extends beyond simple data corruption, as it can enable attackers to manipulate core JavaScript behaviors and potentially execute arbitrary code within the application context. When an application uses immer for state management and processes untrusted input without proper sanitization, an attacker could craft payloads that modify prototype properties to alter how the application handles data. This could lead to denial of service conditions, data manipulation, or even remote code execution depending on the application's architecture. The vulnerability is particularly concerning in server-side JavaScript environments where immer is commonly used for handling user-provided data structures. The flaw can be exploited through various vectors including API endpoints that accept JSON payloads, form submissions, or any interface that allows external data to be processed through the library's state management functions.
Mitigation strategies for this prototype pollution vulnerability in the immer library involve multiple layers of defense. Developers should ensure they are using the latest version of the library where the vulnerability has been patched, as the maintainers have addressed this specific issue in updated releases. Input validation and sanitization should be implemented at all boundaries where user data enters the application, particularly when processing objects that will be passed to immer functions. The use of defensive programming techniques such as avoiding direct property assignment to objects that may contain user input, implementing prototype guard checks, and employing Object.freeze or Object.seal on critical objects can help prevent exploitation. Additionally, security monitoring should be implemented to detect unusual property modifications in prototype chains, and application-level firewalls or web application firewalls should be configured to filter suspicious payloads that attempt to manipulate prototype properties. Organizations should also consider implementing automated security scanning tools that can detect such vulnerabilities during development and deployment phases, ensuring that prototype pollution issues are identified and resolved before they can be exploited in production environments.