alanh0 research blog: ebctf 2013 For-100 write up

Challenge:

After a recent attack, we found this encrypted file. Luckily, we made a memory dump, can you decrypt the file?
Archive password: lcoXse3oa3Uicioc

Files can also be found here: http://ctf.zone/EbCTF-2013-08/Forensics/100/

Download and unzip the memory dump, check the file type

Also check the strings, so it could be linux 64 bit

Pre-requisites:
We will be using volatility to investigate the memory dump, and a suitable linux profile to read it. In this case, for convenience, we can simply download Ubuntu 12.04 64bit and run it in VM
http://www.ubuntu.com/download/desktop/questions?distro=desktop&bits=64&release=lts
after setting up the VM for Ubuntu, we will install volatility (you may also need to install subversion beforehand)
in Ubuntu 64bit open the terminal, to install subversion:
$ sudo apt-get install subversion
To install volatility:
sudo svn checkout http://volatility.googlecode.com/svn/trunk/ volatility
$ cd volatility
$ sudo python setup.py install
*note: the path in the sample codes may be different (subject to your own environment)

To create Linux Profile (Ubuntu1204-64bit) for read the memory dump
ref: https://code.google.com/p/volatility/wiki/LinuxMemoryForensics

To install dwarfdump:
$ apt-get install dwarfdum
$ cd volatility/tools/linux
$ make
$ head module.dwarf

Making the profile:

From above, we found “BOOT_IMAGE=/boot/vmlinuz-3.5.0-23-generic”, we may create the profile from Ubuntu12.04 64bit with System.map-3.5.0-23-generic

$ sudo zip volatility/volatility/plugins/overlays/linux/Ubuntu1204.zip volatility/tools/linux/module.dwarf /boot/System.map-3.5.0-23-generic

Ubuntu1204.zip will be created, we can see “LinuxUbuntu1204x64” profile

$ python vol.py --info | grep Linux

Everything is ready, we can analyze the memory dump, There's a python2 process (pid=1317), we will want to examine it further
$ python vol.py --profile=LinuxUbuntu1204x64 -f memory.dump linux_pslist

We will use linux_bash to check for any clues in the history
$ python vol.py --profile=LinuxUbuntu1204x64 -f memory.dump linux_bash

Two important findings here,
python2 ctf.py ‘ i hide my ‘
kill -s SIGUSR 1317
the python was executed with argument “ i hide my”, and eventually the process was killed by SIGUSR1

The python code could still be in the memory, so we grep the strings
$strings memory.dump | grep SIGUSR1

“signal.signal(signal.SIGUSR1, encrypt)” seems to be part of the python
We save the strings in a text file and do another search for the rest of the codes
$ strings memory.dump > memory.dump.txt
Search the string “signal.signal(signal.SIGUSR1, encrypt)” in text editor, we could find the python codes around
Now we’ve got key1: ‘is this where’, key2: ‘ i hide my ’, and now we have to find key3 in order to decrypt the “flag” file

We try examine the python process memory for what could be input as argument
$ python vol.py --profile=LinuxUbuntu1204x64 -f memory.dump linux_proc_maps -p 1317
We see “[heap]” between python2 and encrypt, it could be string of the input

We dump the memory for further analysis
$ python vol.py --profile=LinuxUbuntu1204x64 -f memory.dump linux_dump_map -p 1317 –dump-dir output/
$ grep -r 'i hide my' output/
These two files should contain “i hide my”, Let’s search the strings in these two files
Ha! We got sth. useful! ‘is this where i hide my secrets?’, so key3 is “secrets”!

You may also simply search for memory.dump strings to find “is this where i hide my secrets”