CVE-2021-43787 in Nodebb
Summary
by MITRE • 11/29/2021
Nodebb is an open source Node.js based forum software. In affected versions a prototype pollution vulnerability in the uploader module allowed a malicious user to inject arbitrary data (i.e. javascript) into the DOM, theoretically allowing for an account takeover when used in conjunction with a path traversal vulnerability disclosed at the same time as this report. The vulnerability has been patched as of v1.18.5. Users are advised to upgrade as soon as possible.
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Analysis
by VulDB Data Team • 12/02/2021
The vulnerability CVE-2021-43787 represents a critical prototype pollution flaw within the NodeBB forum software ecosystem, specifically affecting the uploader module component. This issue arises from improper handling of user-supplied input during file upload operations, where the application fails to adequately sanitize or validate object properties before incorporating them into the application's prototype chain. The vulnerability exists in versions prior to 1.18.5 and demonstrates a fundamental weakness in the software's input validation mechanisms, allowing malicious actors to manipulate the prototype of JavaScript objects through crafted payloads. The affected NodeBB platform, being built on Node.js technology, inherits inherent risks associated with prototype manipulation in server-side JavaScript environments where object properties can be dynamically modified.
The technical exploitation of this prototype pollution vulnerability enables attackers to inject arbitrary JavaScript code into the application's data structures, potentially allowing for DOM-based code execution when combined with other vulnerabilities present in the same software ecosystem. When combined with a path traversal vulnerability disclosed simultaneously, the attack surface expands significantly, as the prototype pollution can be leveraged to manipulate application behavior and potentially escalate privileges. The vulnerability stems from the application's failure to properly isolate user input from internal object properties, creating a scenario where malicious data can pollute the prototype chain and subsequently affect all instances of that object type. This flaw directly aligns with CWE-471, which specifically addresses the issue of prototype pollution in programming languages that support dynamic object manipulation. The exploitation process typically involves sending specially crafted requests that manipulate object properties during deserialization or data processing phases, leading to unexpected behavior in the application's execution flow.
The operational impact of CVE-2021-43787 extends beyond simple data corruption or denial of service, as it creates a persistent security risk that can be weaponized for account takeover operations. When combined with path traversal vulnerabilities, attackers can potentially manipulate file system operations to execute arbitrary code, gain unauthorized access to user accounts, or compromise the entire forum infrastructure. The vulnerability affects the core functionality of NodeBB's file upload system, which is essential for user interaction and content management within the platform. Organizations running affected versions of NodeBB face significant exposure to malicious actors who can exploit this weakness to establish persistent access to their forums, potentially compromising user data, forum integrity, and system availability. The attack vector typically involves uploading malicious files or sending crafted HTTP requests that trigger the prototype pollution during the file processing workflow, making this vulnerability particularly dangerous in environments where user uploads are permitted and not adequately filtered.
Security mitigations for CVE-2021-43787 require immediate remediation through upgrading to NodeBB version 1.18.5 or later, which includes patches addressing the prototype pollution vulnerability in the uploader module. System administrators should implement comprehensive input validation measures, including sanitizing all user-supplied data before processing and implementing strict object property validation during deserialization operations. The solution aligns with ATT&CK technique T1059.007 for JavaScript, as the vulnerability enables code injection through prototype manipulation, and T1566 for social engineering, since the attack often involves manipulating user interactions with file upload mechanisms. Organizations should also consider implementing additional defensive measures such as Content Security Policy headers, input sanitization libraries, and regular security audits of application components that handle user uploads. The patch addresses the root cause by ensuring that object properties are properly validated and that user input cannot modify prototype properties, thereby preventing the injection of malicious code into the application's execution context. Regular monitoring and vulnerability assessment of NodeBB installations should be conducted to prevent similar issues from arising in the future, particularly focusing on the validation of object properties during file processing operations and ensuring proper isolation of user data from core application structures.