Source: cve-assign@fb.com
The hhvm-attach deep link handler in Nuclide did not properly sanitize the provided hostname parameter when rendering. As a result, a malicious URL could be used to render HTML and other content inside of the editor's context, which could potentially be chained to lead to code execution. This issue affected Nuclide prior to v0.290.0.
Nuclide, a code editor, is vulnerable to a cross-site scripting (XSS) attack due to improper sanitization of user-supplied input in its hhvm-attach deep link handler. This flaw allows attackers to inject malicious HTML and JavaScript into the editor's context, potentially leading to remote code execution (RCE) and complete system compromise.
Step 1: Payload Delivery: The attacker crafts a malicious URL containing JavaScript within the hostname parameter of the hhvm-attach deep link. This URL is designed to exploit the XSS vulnerability.
Step 2: User Interaction: The attacker lures a Nuclide user into clicking the malicious URL. This could be through phishing, social engineering, or other means.
Step 3: Handler Invocation: When the user clicks the URL, the hhvm-attach deep link handler within Nuclide is triggered.
Step 4: Parameter Processing: The handler receives the hostname parameter, which now contains the attacker's JavaScript payload.
Step 5: Unsanitized Rendering: The handler renders the hostname parameter, including the attacker's JavaScript, within the editor's context without proper sanitization or encoding.
Step 6: Code Execution: The user's browser executes the injected JavaScript, allowing the attacker to perform malicious actions within the editor's environment.
The vulnerability stems from a lack of proper input validation and output encoding within the hhvm-attach deep link handler in Nuclide. Specifically, the handler fails to sanitize the hostname parameter before rendering it within the editor's context. This allows an attacker to craft a malicious URL containing JavaScript code. When a user clicks on this crafted URL, the injected JavaScript executes within the context of the editor, enabling the attacker to manipulate the editor's behavior, steal sensitive information (e.g., source code, authentication tokens), or potentially achieve RCE by exploiting further vulnerabilities within the editor or its associated plugins. The root cause is a missing or inadequate input validation and output encoding mechanism for the hostname parameter. The handler trusts the user-provided input, leading to the XSS vulnerability.
While no specific APTs are directly linked to this CVE, the nature of the vulnerability (XSS leading to potential RCE) makes it attractive to various threat actors. This type of vulnerability can be used in supply chain attacks if the editor is used by a large number of developers. Not listed on CISA KEV.
Monitor network traffic for unusual URLs containing the hhvm-attach scheme with suspicious hostname parameters, such as those containing JavaScript code (e.g., <script>, onerror, onload).
Analyze editor logs for unusual activity related to the hhvm-attach handler, including attempts to load external resources or execute commands.
Implement a Web Application Firewall (WAF) to filter malicious requests containing XSS payloads.
Monitor for changes in the editor's behavior or unexpected pop-up windows, which could indicate a successful XSS attack.
Examine the editor's configuration files for any unauthorized modifications or changes to the hhvm-attach handler's settings.
Upgrade Nuclide to version 0.290.0 or later. This version includes a fix for the vulnerability.
Implement robust input validation to sanitize all user-supplied input, particularly the hostname parameter, before rendering it within the editor's context.
Employ output encoding (e.g., HTML encoding) to prevent the execution of malicious code within the editor's context.
Review and harden the editor's security configuration, including disabling unnecessary features and restricting access to sensitive resources.
Implement a Content Security Policy (CSP) to restrict the sources from which the editor can load resources, mitigating the impact of XSS attacks.
Regularly scan the editor and its dependencies for known vulnerabilities.