CVE-2020-13697 in NanoHTTPD
Summary
by MITRE • 02/23/2021
An issue was discovered in RouterNanoHTTPD.java in NanoHTTPD through 2.3.1. The GeneralHandler class implements a basic GET handler that prints debug information as an HTML page. Any web server that extends this class without implementing its own GET handler is vulnerable to reflected XSS, because the GeneralHandler GET handler prints user input passed through the query string without any sanitization.
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Analysis
by VulDB Data Team • 03/04/2021
The vulnerability identified as CVE-2020-13697 resides within the RouterNanoHTTPD.java component of the NanoHTTPD web server framework version 2.3.1 and earlier. This issue represents a critical security flaw that affects systems utilizing the GeneralHandler class as part of their web server implementation. The vulnerability stems from inadequate input validation and sanitization practices within the framework's core HTTP handling mechanisms, creating an environment where malicious actors can exploit reflected cross-site scripting vulnerabilities through simple web requests.
The technical flaw manifests in the GeneralHandler class's GET method implementation which directly incorporates user-supplied query parameters into HTML output without any form of sanitization or encoding. When a web server extends the NanoHTTPD framework and relies on the default GeneralHandler for GET requests, any user input passed through the query string parameters becomes immediately embedded into the generated HTML response. This behavior creates a classic reflected XSS vulnerability where an attacker can craft malicious URLs containing script payloads that execute in the context of other users' browsers when they access the vulnerable endpoint.
The operational impact of this vulnerability extends beyond simple information disclosure or session hijacking. Attackers can leverage this reflected XSS vulnerability to perform various malicious activities including but not limited to stealing user session cookies, redirecting victims to malicious websites, defacing web pages, or executing arbitrary JavaScript code within the victim's browser context. The vulnerability affects any system that utilizes the NanoHTTPD framework without implementing custom GET handlers or without properly sanitizing user inputs, making it particularly dangerous as it can be exploited across numerous applications and services that depend on this lightweight HTTP server implementation.
From a cybersecurity perspective, this vulnerability aligns with CWE-79 which specifically addresses cross-site scripting flaws, and maps to ATT&CK technique T1203 - Exploitation for Client Execution. The vulnerability's exploitation requires minimal technical expertise and can be automated through simple URL manipulation, making it particularly attractive to attackers seeking quick gains. Organizations using affected versions of NanoHTTPD should immediately assess their deployment environments and implement proper input sanitization measures. The recommended mitigations include upgrading to patched versions of the framework, implementing proper HTML encoding of all user-supplied inputs before rendering, and potentially employing Content Security Policy headers as additional defense-in-depth measures to limit the potential impact of any remaining vulnerabilities.
The broader implications of this vulnerability highlight the importance of secure coding practices in web frameworks and the critical need for proper input validation at all levels of application development. This issue demonstrates how seemingly innocuous debugging features can become security liabilities when not properly secured, emphasizing the necessity of comprehensive security testing and code review processes for all components, particularly those handling user input. Organizations should also consider implementing automated vulnerability scanning tools that can identify such insecure coding patterns within their codebases and ensure that all third-party libraries are kept up to date with security patches to prevent exploitation of known vulnerabilities.