CVE-2018-16471 in Rack
Summary
by MITRE
There is a possible XSS vulnerability in Rack before 2.0.6 and 1.6.11. Carefully crafted requests can impact the data returned by the `scheme` method on `Rack::Request`. Applications that expect the scheme to be limited to 'http' or 'https' and do not escape the return value could be vulnerable to an XSS attack. Note that applications using the normal escaping mechanisms provided by Rails may not impacted, but applications that bypass the escaping mechanisms, or do not use them may be vulnerable.
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Analysis
by VulDB Data Team • 06/06/2023
The vulnerability identified as CVE-2018-16471 represents a cross-site scripting weakness within the Rack web application framework that affects versions prior to 2.0.6 and 1.6.11. This issue stems from improper handling of the scheme method in Rack::Request objects, where maliciously crafted HTTP requests can manipulate the scheme value in ways that bypass normal security controls. The flaw specifically targets applications that rely on the scheme method to return only 'http' or 'https' values without adequate sanitization or escaping mechanisms. The vulnerability operates at the HTTP request parsing level where the scheme component of URLs is processed, making it particularly insidious as it can be exploited through seemingly benign request parameters that are then interpreted as part of the scheme value.
The technical implementation of this vulnerability involves the manipulation of HTTP request parsing logic within Rack's request handling mechanism. When applications parse incoming requests and subsequently call the scheme method on Rack::Request objects, malicious input can cause the method to return unexpected scheme values that contain embedded script tags or other malicious content. This occurs because the framework does not properly validate or sanitize the scheme component of requests before returning it to applications. The vulnerability falls under CWE-79 - Improper Neutralization of Input During Web Page Generation, specifically targeting the improper handling of user-controllable input that gets reflected in web responses without adequate sanitization. The flaw demonstrates a classic case of insufficient input validation and output encoding in web application security.
The operational impact of this vulnerability extends beyond simple XSS exploitation to potentially compromise entire web applications that rely on Rack for request processing. Applications that do not properly escape the scheme method's return value become vulnerable to attacks where malicious users can inject script code through carefully crafted requests that modify the scheme component. This creates a vector for attackers to execute arbitrary JavaScript code in the context of the victim's browser, potentially leading to session hijacking, data theft, or further exploitation of the affected application. The vulnerability is particularly dangerous in environments where applications bypass Rails' built-in escaping mechanisms, as mentioned in the original description, since these applications lack the additional protection layers that would normally prevent such attacks from succeeding.
Mitigation strategies for CVE-2018-16471 primarily focus on upgrading to affected versions of Rack that contain the necessary patches, specifically versions 2.0.6 and 1.6.11 or later. Organizations should implement comprehensive patch management procedures to ensure all affected systems receive updates promptly. Additionally, applications should adopt defensive programming practices including input validation and output escaping for all user-controllable data, even when using frameworks that provide built-in protection mechanisms. The implementation of Content Security Policy headers can provide additional protection layers against XSS attacks, while proper request validation and sanitization should be implemented at multiple points in the application stack. Security teams should also consider implementing web application firewalls that can detect and block suspicious request patterns that may attempt to exploit this vulnerability, particularly focusing on unusual scheme values in HTTP requests. The ATT&CK framework categorizes this as a web application vulnerability exploitation technique under the T1190 - Exploit Public-Facing Application tactic, emphasizing the need for robust application security controls and regular vulnerability assessments to prevent such attacks from succeeding.