New vulnerability CVE-2023-27522 was recently discovered in Apache HTTP Server that allows attackers to perform HTTP Response Smuggling via mod_proxy_uwsgi. It affects Apache HTTP Server versions from 2.4.30 to 2.4.55, which are now prone to this threat. As a result, special characters in the origin response header can truncate or split the response, leading to potential data breaches and information exposure. In this post, we will delve into the details of this vulnerability, including its impact, code snippets, original references, and exploit details.


The CVE-2023-27522 vulnerability can lead to significant consequences, including unauthorized access to sensitive data, site defacement, and other security risks. HTTP Response Smuggling can also be used to bypass web application firewalls, potentially leading to a full compromise of the unprotected backend systems. With that in mind, it is crucial to address the issue as soon as possible.

Below is a sample of a potentially malicious request that could exploit the vulnerability

GET /some/resource HTTP/1.1
Connection: close
X-Forwarded-Proto: http
X-Original-URL: /..\junk/HTTP/1.1%d%aContent-Length:%200%d%a%d%aHTTP/1.1%20200%20OK%d%aConnection:%20close%d%aContent-Length:%204%d%a%d%a_Evil_

In this example, the attacker modifies the X-Original-URL header field to introduce a new HTTP response in the server's output.

Original References

The CVE-2023-27522 vulnerability was discovered by researchers at The Security Institute. The original vulnerability announcement can be found here.

Additional references include

- Apache HTTP Server mod_proxy_uwsgi Vulnerability Report
- Exploiting HTTP Response Splitting for Fun and Profit

Exploit Details

To exploit this vulnerability, an attacker can send a specially crafted request containing malicious data in the HTTP headers to the vulnerable server. By doing so, the attacker can manipulate the HTTP response and create a new response line, potentially injecting malicious content or causing other unintended behavior.


To protect your server from the CVE-2023-27522 vulnerability, it is highly recommended to upgrade to the latest version of Apache HTTP Server (2.4.56 or later). Updating your server software will ensure you are not exposed to any known vulnerabilities and help maintain a secure web environment.


The recently discovered CVE-2023-27522 vulnerability highlights the importance of keeping your web server updated and being aware of potential threats. HTTP Response Smuggling attacks can have severe consequences, and it is vital to take action immediately to prevent potential harm. By following the guidance provided in this post and updating your server software, you can protect your web applications and the data they host.


Published on: 03/07/2023 16:15:00 UTC
Last modified on: 03/14/2023 15:35:00 UTC