CVE-2022-45442 in Sinatra
Summary
by MITRE • 11/29/2022
Sinatra is a domain-specific language for creating web applications in Ruby. An issue was discovered in Sinatra 2.0 before 2.2.3 and 3.0 before 3.0.4. An application is vulnerable to a reflected file download (RFD) attack that sets the Content-Disposition header of a response when the filename is derived from user-supplied input. Version 2.2.3 and 3.0.4 contain patches for this issue.
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Analysis
by VulDB Data Team • 11/05/2025
Sinatra is a lightweight web application framework written in Ruby that provides a domain-specific language for building web applications. The framework gained popularity for its simplicity and flexibility in creating RESTful APIs and web services. However, a critical vulnerability was identified in versions prior to 2.2.3 and 3.0.4 that exposes applications built with this framework to reflected file download attacks. This vulnerability stems from improper handling of user-supplied input when constructing the Content-Disposition header in HTTP responses. The Content-Disposition header is used to indicate whether the content should be displayed inline in the browser or downloaded as a file, and when combined with user-provided filenames, it creates a dangerous attack surface.
The technical flaw in this vulnerability occurs when Sinatra applications process user input to generate filenames for file downloads. Specifically, when the framework constructs the Content-Disposition header using unvalidated user input, attackers can inject malicious filenames that trigger unintended file download behavior. This creates a reflected file download scenario where an attacker can craft a malicious URL that, when visited by a victim, prompts the browser to download a file with a malicious filename. The vulnerability is classified as a reflected file download attack because the malicious content is reflected from the user input back to the victim's browser. This type of vulnerability is categorized under CWE-434, which specifically addresses "Unrestricted Upload of File with Dangerous Type" and falls under the broader category of insecure file handling practices in web applications.
The operational impact of this vulnerability is significant as it allows attackers to potentially deliver malicious files to unsuspecting users through social engineering or by exploiting legitimate application functionality. When users click on malicious links, their browsers may download files with deceptive names that could appear to be legitimate documents or executables. The attack can be particularly dangerous if the malicious filename includes file extensions that trigger automatic execution or if the downloaded file contains malicious code that can compromise the user's system. This vulnerability can be exploited in various contexts including phishing campaigns, drive-by download attacks, or by targeting specific applications that legitimately offer file download functionality. The reflected nature of the attack means that the malicious payload is not stored on the server but is instead generated dynamically from user input, making it harder to detect through traditional security scanning methods.
The security implications extend beyond simple file downloads as this vulnerability can be leveraged to bypass certain security controls that rely on filename validation or content type checking. Attackers can potentially craft filenames that exploit browser-specific behaviors or use Unicode characters to obfuscate malicious intent. The vulnerability also demonstrates poor input validation practices that can be exploited in similar ways across different web frameworks. Organizations using Sinatra versions prior to 2.2.3 or 3.0.4 should immediately implement patches as recommended by the maintainers. The fix involves proper sanitization and validation of user input before constructing the Content-Disposition header, ensuring that filenames cannot contain potentially dangerous characters or sequences. This vulnerability aligns with ATT&CK technique T1195.001 which covers "Phishing: Spearphishing Attachment" and represents a common vector for delivering malware through web-based attacks.
The patched versions of Sinatra 2.2.3 and 3.0.4 address this vulnerability by implementing stricter validation of user-supplied filenames in the Content-Disposition header generation process. Security practitioners should verify that their applications are not vulnerable by checking the installed Sinatra version and ensuring proper patching has been applied. Additional mitigations include implementing proper input validation at multiple layers, using security headers to control file handling behavior, and monitoring application logs for suspicious file download patterns. Organizations should also consider implementing web application firewalls or security scanning tools that can detect and block malicious file download attempts. The vulnerability serves as a reminder of the importance of proper input validation and output encoding in web applications, particularly when dealing with user-supplied data that can influence HTTP response headers. Regular security audits and dependency updates are crucial to maintaining application security and preventing exploitation of known vulnerabilities.