A security vulnerability with identifier CVE-2024-38809 has been discovered in applications that parse Entity Tags (ETags) from "If-Match" or "If-None-Match" request headers. This vulnerability can lead to a Denial-of-Service (DoS) attack on the server by an attacker sending requests with maliciously crafted headers.

Exploit Details

ETags are a mechanism used in web applications to determine whether the requested resource has been modified since the last time it was accessed by the client. "If-Match" and "If-None-Match" headers are used to provide conditional requests, enabling the server to apply a specific action depending on the status of the resource.

The vulnerability lies in the affected applications' handling of these headers when parsing ETags. Due to inadequate input validation and boundary checks, an attacker can send requests with specially crafted "If-Match" or "If-None-Match" headers that consume excessive system resources, eventually leading to a DoS condition.

A code snippet demonstrating the exploit might look like this

import requests

target_url = "http://vulnerable-server.com/resource";

# Create a specially crafted header containing a huge ETag value
malicious_etag = "W/\"" + "A" * 100000 + "\""
headers = {"If-None-Match": malicious_etag}

# Send the request with the malicious header
response = requests.get(target_url, headers=headers)

This code snippet sends an HTTP GET request with a crafted "If-None-Match" header containing an excessively large ETag value to the target server, causing the server to use a substantial amount of resources processing the header.

Original References

The vulnerability has been acknowledged by the developers of the affected applications and has been assigned the identifier CVE-2024-38809. Details about the vulnerability can be found in the following resources:

- CVE-2024-38809 Official Entry
- NVD Entry for CVE-2024-38809

Mitigation and Remediation

Users of affected versions should upgrade to the corresponding fixed version of the software to address this vulnerability. The developers have released patches that implement proper validation and checks when parsing ETags from "If-Match" and "If-None-Match" request headers, making them resilient to this DoS attack.

For users who are on older, unsupported versions of the software, a possible workaround could be enforcing a size limit on "If-Match" and "If-None-Match" headers. You can achieve this by implementing a Filter in your application. Here is a Java example of how to implement such a filter:

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;
import java.util.Enumeration;

public class ETagSizeLimitFilter implements Filter {

    private static final int MAX_HEADER_SIZE = 1024; // Adjust this value based on your requirements

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {}

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest httpRequest = (HttpServletRequest) request;
        Enumeration<String> headerNames = httpRequest.getHeaderNames();

        while (headerNames.hasMoreElements()) {
            String headerName = headerNames.nextElement();
            String headerValue = httpRequest.getHeader(headerName);

            if (("If-Match".equalsIgnoreCase(headerName) || "If-None-Match".equalsIgnoreCase(headerName)) && headerValue.length() > MAX_HEADER_SIZE) {
                throw new ServletException("Header size limit exceeded");
            }
        }

        chain.doFilter(request, response);
    }

    @Override
    public void destroy() {}
}

By implementing this ETagSizeLimitFilter and adding it to your application's filter chain, incoming requests with "If-Match" or "If-None-Match" headers that exceed the MAX_HEADER_SIZE limit will be rejected with a ServletException.

Timeline

Published on: 09/27/2024 17:15:12 UTC
Last modified on: 11/21/2024 09:26:51 UTC