CVE-2017-16224 in ST
Summary
by MITRE
st is a module for serving static files. An attacker is able to craft a request that results in an HTTP 301 (redirect) to an entirely different domain. A request for: http://some.server.com//nodesecurity.org/%2e%2e would result in a 301 to //nodesecurity.org/%2e%2e which most browsers treat as a proper redirect as // is translated into the current schema being used. Mitigating factor: In order for this to work, st must be serving from the root of a server (/) rather than the typical sub directory (/static/) and the redirect URL will end with some form of URL encoded .. ("%2e%2e", "%2e.", ".%2e").
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Analysis
by VulDB Data Team • 02/16/2020
The vulnerability identified as CVE-2017-16224 resides within the st module, a Node.js library designed for serving static files. This module operates as a middleware component in web applications, handling requests for static resources such as images, CSS files, and JavaScript assets. The flaw manifests in how the module processes URL paths containing specific sequences of encoded characters, creating a path traversal condition that can be exploited to manipulate HTTP redirect responses. The vulnerability specifically affects the module's handling of double-dot sequences in URLs, which are typically used to navigate up directory levels in file systems. When processing requests with these sequences, the st module fails to properly sanitize the input, allowing attackers to construct malicious URLs that result in unintended redirects to external domains.
The technical implementation of this vulnerability stems from inadequate input validation and path normalization within the st module's request handling logic. When an attacker crafts a request such as http://some.server.com//nodesecurity.org/%2e%2e, the module processes the URL components without proper sanitization of the encoded dot-dot sequences. The %2e%2e represents URL-encoded periods and dots, which when decoded become .. characters that typically indicate directory traversal in file systems. The vulnerability exploits the fact that the module does not properly canonicalize these paths before generating redirect responses, allowing the encoded sequences to persist in the redirect URL. This creates a scenario where the HTTP 301 redirect points to a location that browsers interpret as a proper external domain redirect, effectively enabling open redirect attacks.
The operational impact of this vulnerability extends beyond simple redirection, as it can be leveraged for various malicious activities including phishing attacks, credential theft, and social engineering campaigns. The vulnerability requires specific conditions to be exploitable, namely that the st module must be configured to serve content from the root directory of a web server rather than a subdirectory such as /static/. This restriction limits the attack surface but does not eliminate the risk entirely. The attack vector becomes particularly dangerous when combined with other techniques, as the open redirect can be used to funnel users to malicious domains that appear to originate from legitimate sources. The URL encoding pattern of "%2e%2e", "%2e.", and ".%2e" represents the specific sequences that trigger the vulnerability, making it somewhat predictable but still requiring careful crafting of attack payloads. Security researchers have classified this vulnerability under CWE-601, which describes open redirect vulnerabilities in web applications.
The mitigation strategies for this vulnerability primarily involve updating the st module to a patched version that properly sanitizes URL paths and implements proper input validation. Organizations should immediately upgrade to the latest stable release of the module, as the vulnerability has been addressed in subsequent versions through enhanced path canonicalization and input sanitization. Additionally, implementing proper access controls and restricting the st module's serving directory to subdirectories rather than root paths can significantly reduce the attack surface. Network-level protections such as web application firewalls can also detect and block malicious URL patterns, though these should complement rather than replace proper software updates. From an ATT&CK framework perspective, this vulnerability maps to T1566, which covers social engineering techniques involving open redirects, and T1071, which encompasses application layer protocol usage. Organizations should also consider implementing automated security scanning tools that can detect vulnerable module versions and monitor for exploitation attempts through network traffic analysis. The vulnerability demonstrates the importance of proper input validation in web applications and highlights the need for comprehensive security testing of third-party libraries used in production environments.