CVE-2018-11627 in Sinatra
Summary
by MITRE
Sinatra before 2.0.2 has XSS via the 400 Bad Request page that occurs upon a params parser exception.
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Analysis
by VulDB Data Team • 03/19/2023
Sinatra is a lightweight web application framework written in ruby that is widely used for building web applications and APIs. The vulnerability described in CVE-2018-11627 represents a cross-site scripting flaw that affects versions prior to 2.0.2 of the framework. This vulnerability manifests when the application encounters a parameter parsing exception during request processing, which triggers the display of a 400 Bad Request error page. The flaw occurs because the framework fails to properly sanitize user input before rendering it in the error page context, creating an avenue for malicious actors to inject arbitrary javascript code that executes in the context of other users' browsers.
The technical implementation of this vulnerability stems from the way Sinatra handles parameter parsing failures within its request processing pipeline. When malformed parameters are submitted to a Sinatra application, the framework attempts to parse these parameters and when it encounters an exception, it displays a default error page containing information about the failed parsing attempt. This error page construction process does not adequately escape or sanitize the parameter values that caused the exception, allowing malicious input to be rendered directly into the html output. The vulnerability is categorized under CWE-79 as it represents a failure to sanitize user input before rendering it in a web page context, making it susceptible to cross-site scripting attacks. Attackers can exploit this by crafting malicious parameter values that contain javascript payloads, which then execute when other users view the error page.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to perform session hijacking, deface web applications, steal sensitive user data, or redirect users to malicious sites. The vulnerability is particularly concerning because it can be triggered by simply sending malformed parameters to any Sinatra application, requiring no authentication or specialized knowledge of the application's internal workings. This makes it an attractive target for automated scanning tools and opportunistic attackers. The attack surface is broad since any application using Sinatra versions before 2.0.2 is potentially vulnerable, regardless of the specific application logic or security controls in place. The vulnerability can be exploited through various vectors including direct http requests, web application firewalls bypass techniques, and even through legitimate user interactions if the application accepts user input that is then processed through the parameter parser.
Mitigation strategies for this vulnerability involve upgrading to Sinatra version 2.0.2 or later, which includes proper input sanitization in the error handling routines. Organizations should also implement comprehensive input validation at multiple layers of their application architecture, including early filtering of parameters before they reach the framework's parser. Additional defensive measures include implementing content security policies to limit script execution, using proper output encoding when rendering any user-provided content, and deploying web application firewalls that can detect and block malicious parameter patterns. The vulnerability demonstrates the importance of secure error handling practices and aligns with ATT&CK technique T1211 which covers the exploitation of input validation weaknesses. Regular security assessments and dependency monitoring should be implemented to ensure all applications remain protected against similar vulnerabilities, as this flaw represents a common class of issues found in web frameworks where error handling and input sanitization are not properly coordinated.