CVE-2023-28755 is a ReDoS (Regular Expression Denial of Service) issue discovered in the URI component up to version .12.. This vulnerability affects the popular programming language Ruby up to version 3.2.1. The URI parser in Ruby mishandles specific characters in invalid URLs, which leads to a significant increase in execution time for parsing strings into URI objects. To fix this issue, users must update to the fixed versions: .12.1, .11.1, .10.2, or .10..1.

But what exactly is a ReDoS issue, and how does it affect your Ruby applications? Let's dive in and understand this critical vulnerability, explore code snippets, and provide necessary resources for safeguarding your programs.

Understanding ReDoS

A ReDoS attack is a form of denial of service that exploits the regular expression (regex) implementation in target systems. By providing specially crafted input strings, an attacker can cause the resolution of a regular expression to take an excessive amount of time. As a result, the application becomes unresponsive or unavailable to legitimate users.

Exploiting CVE-2023-28755

In the case of CVE-2023-28755, the URI parser in Ruby mishandles specific characters in invalid URLs, leading to a dramatic increase in execution time for parsing strings to URI objects. An attacker may exploit this vulnerability by sending numerous maliciously-formed URLs to a vulnerable application, causing it to become unresponsive or unavailable. The following code snippet is an example of how the URI parser can be triggered:

require 'uri'

def parse_uri(uri_str)
  URI.parse(uri_str)
end

malicious_url = "http://example.com/"; + ("a" * 1_000_000) + "!@#$%^&*()<>?"
parse_uri(malicious_url)

In this example, the malicious_url includes a long sequence of characters followed by specific characters that trigger the ReDoS issue in the URI parser. Calling parse_uri with such a malicious URL can cause the application to become unresponsive or severely degrade its performance.

Fixed Versions and Updating

Thankfully, fixed versions of the URI component are available to Ruby users. Updating to these versions mitigates the ReDoS issue in your applications:

For more information on CVE-2023-28755 and its fixed versions, visit the original references below

- CVE-2023-28755 Official Listing
- Ruby Advisory Database
- Ruby Security Mailing List

In conclusion, the ReDoS issue discovered in the URI component (CVE-2023-28755) poses a significant threat to Ruby applications up to version 3.2.1. Understanding this vulnerability and applying the necessary fixes will help secure your programs and keep your users safe from potential harm.

Timeline

Published on: 03/31/2023 04:15:00 UTC
Last modified on: 05/26/2023 20:15:00 UTC