In this long read, we will dive into the details of a critical security vulnerability CVE-2024-38477, which affects the mod_proxy module in the Apache HTTP Server 2.4.59 and earlier versions. This vulnerability stems from a null pointer dereference issue that could be exploited by an attacker to crash the server by sending a malicious request. To safeguard your system, it is recommended to upgrade to version 2.4.60, which addresses and fixes this issue.

Vulnerability Details

A null pointer dereference occurs when a program attempts to access or modify memory at a null address. This can lead to program crashes or, in certain circumstances, can be exploited by an attacker to compromise the target system.

In CVE-2024-38477, the 'mod_proxy' module in Apache HTTP Server 2.4.59 and earlier has a null pointer dereference vulnerability. This module is used to implement a reverse proxy that forwards incoming HTTP/HTTPS requests to backend servers. This feature is often employed when load balancing web applications or providing access to internal resources.

An attacker can craft a malicious request targeting the reverse proxy and causing a null pointer dereference, which leads to a crash in the Apache HTTP Server. By continually sending such requests, an attacker may cause a denial of service (DoS) attack on the server, rendering it unavailable to other users.

Original References

- The official CVE list entry: https://nvd.nist.gov/vuln/detail/CVE-2024-38477
- Apache HTTP Server official announcement: http://httpd.apache.org/security/vulnerabilities_24.html
- Apache HTTP Server 2.4.60 release notes: https://www.apache.org/dist/httpd/CHANGES_2.4.60

Code Snippet Example

To better understand the code that led to this vulnerability, let us analyze a simplified code snippet that is representative of the issue:

1. void process_request(request_rec *r) {
2.     proxy_worker *worker;
3.     char *url;
4. 
5.     // ... Some code to initialize the worker and URL variables
6. 
7.     if (!worker || !url) { // Check if worker and URL are properly set
8.         return;
9.     }
10.
11.    // ... Some code to process the request
12.}

The critical error occurs at lines 7-9: If the worker or url variables are uninitialized or null, the function returns early, without generating an error. This results in a null pointer dereference, ultimately causing a crash when the server attempts to access memory at a null address.

Exploit Details

While there are no publicly available exploits for CVE-2024-38477, it is essential to remain vigilant and recognize the potential risk. The vulnerability opens the door for attackers to craft a malicious request targeting the reverse proxy, inducing the Apache HTTP Server to crash. Continual malicious requests could lead to a denial of service on the server.

Upgrade to Apache HTTP Server 2.4.60, which includes a fix for this vulnerability.

- Download link: https://httpd.apache.org/download.cgi
- As a temporary measure, ensure that proper input validation and error-handling exist within the 'mod_proxy' module and any custom code interfacing with it.

Conclusion

CVE-2024-38477 is a critical null pointer dereference vulnerability in the 'mod_proxy' module of Apache HTTP Server 2.4.59 and earlier. Ensure to upgrade your server to version 2.4.60 or implement appropriate safeguards as soon as possible to protect your system from potential attacks. Continually be aware of new vulnerabilities and stay ahead of threats by regularly updating and maintaining your systems and codebases.

Timeline

Published on: 07/01/2024 19:15:05 UTC
Last modified on: 08/21/2024 15:11:30 UTC