CVE-2023-29406 - Understanding the Vulnerability in the HTTP/1 Client and the Importance of Validating Host Headers

A recently discovered security vulnerability, designated as CVE-2023-29406, has been identified in the HTTP/1 client, impacting its ability to properly handle and secure Host headers in HTTP requests. This vulnerability could potentially allow attackers to inject additional headers or even entire requests, leading to a variety of security issues. In this post, we'll explore the details of this vulnerability, its impact, and the steps taken to address it. We'll also provide code snippets to illustrate the issue and potential solutions.

Exploit Details

The vulnerability lies in the way the HTTP/1 client processes the Host header in HTTP/1 requests. When a malformed Host header is received, the client fails to properly validate its contents, enabling adversaries to manipulate the header and inject additional headers, potentially compromising the integrity of the overall HTTP request.

Let's take a look at a code snippet showcasing the vulnerability

package main

import (
	"log"
	"net/http"
)

func main() {
	req, err := http.NewRequest("GET", "http://example.com";, nil)
	if err != nil {
		log.Fatal(err)
	}

	// Malicious Host header
	req.Host = "example.com\r\nInjection-Header: value"

	client := &http.Client{}
	resp, err := client.Do(req)
	if err != nil {
		log.Fatal(err)
	}

	defer resp.Body.Close()
}

In this example, the Host header has been maliciously crafted to include an additional header Injection-Header. When sent through the HTTP/1 client, it will not validate the integrity of the Host header, allowing for the additional header to be processed.

Original References

1. This vulnerability was initially reported and tracked in the CVE database (Common Vulnerabilities and Exposures): CVE-2023-29406
2. The details, along with an explanation of the vulnerability, can also be found in this GitHub issue.

Mitigation and Fix

To address this vulnerability, the HTTP/1 client has been updated to properly validate the Host header contents, refusing to send the request if an invalid Request.Host or Request.URL.Host value is detected. The following code snippet demonstrates the updated behavior in the HTTP/1 client:

package main

import (
    "errors"
    "log"
    "net/http"
)

func isValidHost(host string) bool {
    // Implement proper validation of the Host header here
    return true
}

func main() {
    req, err := http.NewRequest("GET", "http://example.com";, nil)
    if err != nil {
        log.Fatal(err)
    }

    // Malicious Host header
    req.Host = "example.com\r\nInjection-Header: value"

    if !isValidHost(req.Host) || !isValidHost(req.URL.Host) {
        log.Fatal(errors.New("Invalid host header detected"))
    }

    client := &http.Client{}
    resp, err := client.Do(req)
    if err != nil {
        log.Fatal(err)
    }

    defer resp.Body.Close()
}

In this example, any malicious manipulation of the Host header will now be caught through proper validation and will cause the request to be refused before any further processing occurs.

Conclusion

CVE-2023-29406 is a significant vulnerability affecting the HTTP/1 client, with the potential to compromise the integrity of both headers and requests it handles. By ensuring proper validation of the Host header, developers can mitigate the risk of this vulnerability and secure their applications against potential exploits.

Timeline

Published on: 07/11/2023 20:15:00 UTC
Last modified on: 08/14/2023 19:15:00 UTC