CVE-2018-3718 in Serve
Summary
by MITRE
serve node module suffers from Improper Handling of URL Encoding by permitting access to ignored files if a filename is URL encoded.
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Analysis
by VulDB Data Team • 02/16/2020
The CVE-2018-3718 vulnerability affects the serve node module, a popular static file server implementation that handles HTTP requests for serving files from a local directory. This security flaw stems from inadequate validation of URL encoding patterns within the file path handling logic, creating a path traversal attack vector that allows unauthorized access to files that should normally be restricted or ignored by the server configuration. The vulnerability specifically manifests when filenames contain URL encoded characters such as %2F which represents forward slashes, enabling attackers to bypass directory restrictions and access files outside the intended serving directory.
The technical root cause of this vulnerability lies in the improper sanitization of URL encoded paths during file resolution within the serve module's request processing pipeline. When a client makes a request with a URL encoded filename, the module fails to properly decode or validate these encoded sequences before performing file system operations. This flaw allows attackers to craft malicious requests where URL encoded characters are used to manipulate the file path resolution logic, effectively circumventing the intended security boundaries that prevent access to sensitive files such as configuration files, system files, or other restricted resources that should remain hidden from public access.
From an operational impact perspective, this vulnerability presents a significant risk to web applications and development environments that rely on the serve module for static file delivery. Attackers can exploit this weakness to access sensitive information including but not limited to database connection strings, API keys, environment variables, and other confidential data stored in configuration files. The vulnerability is particularly dangerous in development environments where the serve module is often used to quickly serve static content without proper security hardening, potentially exposing sensitive source code or system information that could be leveraged for further attacks within the network infrastructure. The impact extends beyond simple information disclosure as it can enable attackers to potentially execute additional attacks through access to system files or configuration data.
Security professionals should address this vulnerability by implementing proper input validation and sanitization mechanisms that ensure URL encoded sequences are properly handled before file system operations occur. The recommended mitigation strategies include updating to patched versions of the serve module where available, implementing explicit URL decoding validation that prevents path traversal attempts, and configuring proper file access controls that restrict access to sensitive files regardless of URL encoding patterns. Organizations should also consider implementing web application firewalls or security middleware that can detect and block suspicious URL encoding patterns. This vulnerability aligns with CWE-22 Path Traversal and CWE-77 Path Traversal, and represents a technique that could be categorized under ATT&CK tactic TA0001 Initial Access and TA0002 Execution, as it enables attackers to gain access to system resources that could be used for further compromise of the affected systems.