Abusing Intermediary Applications

AJP Proxy

When we come across open AJP proxy ports (8009 TCP) during penetration tests, we may be able to use them to access the "hidden" Apache Tomcat Manager behind it. Although AJP-Proxy is a binary protocol, we can configure our own Nginx or Apache webserver with AJP modules to interact with it and access the underlying application. This way, we can discover administrative panels, applications, and websites that would be otherwise inaccessible.

Docker Installation

sudo apt install docker
sudo docker run -it --rm -p 8009:8009 -v `pwd`/tomcat-users.xml:/usr/local/tomcat/conf/tomcat-users.xml --name tomcat "tomcat:8.0"

Nginx Reverse Proxy & AJP

When we come across an open AJP proxy port (8009 TCP), we can use Nginx with the ajp_module to access the "hidden" Tomcat Manager.

Download Nginx Source Code

wget https://nginx.org/download/nginx-1.21.3.tar.gz
tar -xzvf nginx-1.21.3.tar.gz

Compile Nginx source code with the ajp module

Staphy$ git clone https://github.com/dvershinin/nginx_ajp_module.git
Staphy$ cd nginx-1.21.3
Staphy$ sudo apt install libpcre3-dev
Staphy$ ./configure --add-module=`pwd`/../nginx_ajp_module --prefix=/etc/nginx --sbin-path=/usr/sbin/nginx --modules-path=/usr/lib/nginx/modules
Staphy$ make
Staphy$ sudo make install
Staphy$ nginx -V

nginx version: nginx/1.21.3
built by gcc 10.2.1 20210110 (Debian 10.2.1-6)
configure arguments: --add-module=../nginx_ajp_module --prefix=/etc/nginx --sbin-path=/usr/sbin/nginx --modules-path=/usr/lib/nginx/module

Comment out the entire server block and append the following lines inside the http block in /etc/nginx/conf/nginx.conf.

Pointing to the AJP Port: 

upstream tomcats {
	server <TARGET_SERVER>:8009;
	keepalive 10;
	}
server {
	listen 80;
	location / {
		ajp_keep_conn on;
		ajp_pass tomcats;
	}
}

Start Nginx and check if everything is working correctly by issuing a curl request to your local host.

sudo nginx 
curl localhost:80

Apache Reverse Proxy & AJP

Apache has the AJP module precompiled for us. We will need to install it, though, as it doesn't come in default installations. Configuring the AJP-Proxy in our Apache server can be done as follows:

  • Install the libapache2-mod-jk package

  • Enable the module

  • Create the configuration file pointing to the target AJP-Proxy port

The required commands and configuration files are the following:

Staphy$ sudo apt install libapache2-mod-jk
Staphy$ sudo a2enmod proxy_ajp
Staphy$ sudo a2enmod proxy_http
Staphy$ export TARGET="<TARGET_IP>"
Staphy$ echo -n """<Proxy *>
Order allow,deny
Allow from all
</Proxy>
ProxyPass / ajp://$TARGET:8009/
ProxyPassReverse / ajp://$TARGET:8009/""" | sudo tee /etc/apache2/sites-available/ajp-proxy.conf
Staphy@htb[/htb]$ sudo ln -s /etc/apache2/sites-available/ajp-proxy.conf /etc/apache2/sites-enabled/ajp-proxy.conf
Staphy@htb[/htb]$ sudo systemctl start apache2

Accessing the "hidden" Tomcat page

curl http://127.0.0.1

<SNIP>
<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8" />
        <title>Apache Tomcat/X.X.XX</title>
        <link href="favicon.ico" rel="icon" type="image/x-icon" />
        <link href="favicon.ico" rel="shortcut icon" type="image/x-icon" />
        <link href="tomcat.css" rel="stylesheet" type="text/css" />
    </head>

    <body>
        <div id="wrapper">
            <div id="navigation" class="curved container">
                <span id="nav-home"><a href="https://tomcat.apache.org/">Home</a></span>
                <span id="nav-hosts"><a href="/docs/">Documentation</a></span>
                <span id="nav-config"><a href="/docs/config/">Configuration</a></span>
                <span id="nav-examples"><a href="/examples/">Examples</a></span>
                <span id="nav-wiki"><a href="https://wiki.apache.org/tomcat/FrontPage">Wiki</a></span>
                <span id="nav-lists"><a href="https://tomcat.apache.org/lists.html">Mailing Lists</a></span>
                <span id="nav-help"><a href="https://tomcat.apache.org/findhelp.html">Find Help</a></span>
                <br class="separator" />
            </div>
            <div id="asf-box">
                <h1>Apache Tomcat/X.X.XX</h1>
            </div>
            <div id="upper" class="curved container">
                <div id="congrats" class="curved container">
                    <h2>If you're seeing this, you've successfully installed Tomcat. Congratulations!</h2>
                </div>
<SNIP>

If we configure everything correctly, we will be able to access the Apache Tomcat manager using both cURL and our web browser.

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