CGI, Denial of Service (DoS), CVE-2025-27219 (High)

How the Mentioned CVE Works:

CVE-2025-27219 is a high-severity vulnerability in the CGI gem, specifically in the `CGI::Cookie.parse` method. This method is responsible for parsing cookie strings. Due to inefficient parsing logic, it takes super-linear time to process certain maliciously crafted cookie strings. When an attacker sends a specially designed cookie string, the method consumes excessive computational resources, leading to a Denial of Service (DoS) condition. This can render the application unresponsive, disrupting service availability. The vulnerability affects CGI gem versions <= 0.3.5, 0.3.6, 0.4.0, and 0.4.1. Patched versions include 0.3.5.1, 0.3.7, and 0.4.2.

DailyCVE Form:

Platform: Ruby CGI Gem
Version: <= 0.3.5, 0.3.6, 0.4.0, 0.4.1
Vulnerability: Denial of Service (DoS)
Severity: High
Date: Mar 3, 2025

What Undercode Say:

Exploitation:

1. Craft Malicious Cookie: Create a cookie string designed to trigger super-linear parsing.
2. Send to Target: Submit the malicious cookie to a vulnerable application using CGI::Cookie.parse.
3. Observe DoS: The server becomes unresponsive due to excessive resource consumption.

Protection:

1. Update CGI Gem: Upgrade to patched versions (0.3.5.1, 0.3.7, 0.4.2).
2. Input Validation: Implement strict validation for cookie strings.
3. Rate Limiting: Apply rate limits to prevent abuse of the parsing function.

Commands:

1. Check Installed Version:

gem list cgi

2. Update CGI Gem:

gem update cgi

Code Snippets:

1. Patch Application:

Gemfile
gem 'cgi', '>= 0.4.2'

2. Input Validation:

def safe_parse_cookie(cookie_string)
raise "Invalid cookie" if cookie_string.length > 1024
CGI::Cookie.parse(cookie_string)
end

References:

1. GitHub Advisory Database
2. CVE-2025-27219 Details
3. RubyGems CGI Gem

Analytics:

• Impact: High (DoS can disrupt service availability).
• Exploit Complexity: Low (requires minimal technical knowledge).
• Mitigation Difficulty: Low (update to patched versions).

By following these steps, you can protect your application from this vulnerability and ensure its continued availability.

References:

Reported By: https://github.com/advisories/GHSA-gh9q-2xrm-x6qv
Extra Source Hub:
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