CVE-2022-45442: Reflected File Download Vulnerability in Sinatra Web Framework

Sinatra is a popular domain-specific language (DSL) for developing web applications in Ruby. It focuses on simplicity and minimalism, providing a lightweight and fast option for building web applications. However, a recent vulnerability has been discovered in Sinatra that introduces a security risk.

Vulnerability Details

A vulnerability with the identifier CVE-2022-45442 has been found in Sinatra versions 2. before 2.2.3 and 3. before 3..4. This vulnerability exposes the application to a reflected file download (RFD) attack, which manipulates the Content-Disposition header of a response by generating a malicious file name using user-supplied input.

This vulnerability occurs when a Sinatra application directly uses the user-input filename to set the Content-Disposition header. An attacker can exploit this vulnerability to create a malicious file with a name acceptable to the server, which could then be downloaded and executed on the victim's machine.

Consider the following example of a vulnerable Sinatra application

require 'sinatra'
require 'send_file'

get '/download' do
  file_name = params[:file_name]
  send_file "/path/to/files/#{file_name}", :filename => file_name
end

Here, the user supplied input for file_name is used in the Content-Disposition header without any validation or filtering, making the application vulnerable to an RFD attack.

Exploit Details

An attacker can exploit the vulnerability by crafting a URL that includes a malicious filename. For example:

http://vulnerable-app.com/download?file_name=malicious.exe

When a victim clicks on this URL, their browser would download the malicious file and potentially execute it, compromising the victim's system.

Mitigation and Patches

The vulnerability has been patched in Sinatra versions 2.2.3 and 3..4. The official changelog for these versions can be found on the Sinatra GitHub repository:

- Sinatra 2.2.3 Changelog
- Sinatra 3..4 Changelog

Developers using Sinatra should immediately upgrade to the latest version to protect against this vulnerability. Additionally, the following mitigation steps can be taken to protect the application:

Validate and sanitize user-supplied input before using it in the Content-Disposition header.

- Avoid using user-supplied filenames directly in the header; instead, use server-generated filenames or ensure the filename is constrained to a specific format or file extension.

Conclusion

CVE-2022-45442 represents a significant vulnerability in the Sinatra web application framework. Developers should act quickly to update their applications and follow best practices for handling user input to prevent reflected file download attacks. Staying vigilant and making use of the latest security patches will help defend against similar security issues in the future.

Timeline

Published on: 11/28/2022 21:15:00 UTC
Last modified on: 02/01/2023 15:47:00 UTC