On Pins and Needles

Wednesday, April 15, 2020

CEH: System Hacking, Cracking A Password, Understanding The LAN Manager Hash, NetBIOS DoS Attacks

Passwords are the key element of information require to access the system. Similarly, the first step is to access the system is that you should know how to crack the password of the target system. There is a fact that users selects passwords that are easy to guess. Once a password is guessed or cracked, it can be the launching point for escalating privileges, executing applications, hiding files, and covering tracks. If guessing a password fails, then passwords may be cracked manually or with automated tools such as a dictionary or brute-force method.

Cracking a Password

Passwords are stored in the Security Accounts Manager (SAM) file on a Windows system and in a password shadow file on a Linux system.

Manual password cracking involves attempting to log on with different passwords. The hacker follows these steps:

Find a valid user account (such as Administrator or Guest).
Create a list of possible passwords.
Rank the passwords from high to low probability.
Key in each password.
Try again until a successful password is found.

A hacker can also create a script file that tries each password in a list. This is still considered manual cracking, but it's time consuming and not usually effective.

A more efficient way of cracking a password is to gain access to the password file on a system. Most systems hash (one-way encrypt) a password for storage on a system. During the logon process, the password entered by the user is hashed using the same algorithm and then compared to the hashed passwords stored in the file. A hacker can attempt to gain access to the hashing algorithm stored on the server instead of trying to guess or otherwise identify the password. If the hacker is successful, they can decrypt the passwords stored on the server.

Understanding the LAN Manager Hash

Windows 2000 uses NT LAN Manager (NTLM) hashing to secure passwords in transit on the network. Depending on the password, NTLM hashing can be weak and easy to break. For example, let's say that the password is 123456abcdef . When this password is encrypted with the NTLM algorithm, it's first converted to all uppercase: 123456ABCDEF . The password is padded with null (blank) characters to make it 14 characters long: 123456ABCDEF__ . Before the password is encrypted, the 14-character string is split in half: 123456A and
BCDEF__ . Each string is individually encrypted, and the results are concatenated:

123456A = 6BF11E04AFAB197F
BCDEF__ = F1E9FFDCC75575B15

The hash is 6BF11E04AFAB197FF1E9FFDCC75575B15 .

Cracking Windows 2000 Passwords

The SAM file in Windows contains the usernames and hashed passwords. It's located in the Windows\system32\config directory. The file is locked when the operating system is running so that a hacker can't attempt to copy the file while the machine is booted to Windows.

One option for copying the SAM file is to boot to an alternate operating system such as DOS or Linux with a boot CD. Alternately, the file can be copied from the repair directory. If a system administrator uses the RDISK feature of Windows to back up the system, then a compressed copy of the SAM file called SAM._ is created in C:\windows\repair . To expand this file, use the following command at the command prompt:

C:\>expand sam._ sam

After the file is uncompressed, a dictionary, hybrid, or brute-force attack can be run against the SAM file using a tool like L0phtCrack. A similar tool to L0phtcrack is Ophcrack.

Download and install ophcrack from http://ophcrack.sourceforge.net/

Redirecting the SMB Logon to the Attacker

Another way to discover passwords on a network is to redirect the Server Message Block (SMB) logon to an attacker's computer so that the passwords are sent to the hacker. In order to do this, the hacker must sniff the NTLM responses from the authentication server and trick the victim into attempting Windows authentication with the attacker's computer.

A common technique is to send the victim an email message with an embedded link to a fraudulent SMB server. When the link is clicked, the user unwittingly sends their credentials over the network.

SMBRelay

An SMB server that captures usernames and password hashes from incoming
SMB traffic. SMBRelay can also perform man-in-the-middle (MITM) attacks.

SMBRelay2

Similar to SMBRelay but uses NetBIOS names instead of IP addresses to capture usernames and passwords.

pwdump2

A program that extracts the password hashes from a SAM file on a Windows system. The extracted password hashes can then be run through L0phtCrack to break the passwords.

Samdump

Another program that extracts NTLM hashed passwords from a SAM file.

C2MYAZZ

A spyware program that makes Windows clients send their passwords as clear text. It displays usernames and their passwords as users attach to server resources.

NetBIOS DoS Attacks

A NetBIOS denial-of-service (DoS) attack sends a NetBIOS Name Release message to the NetBIOS Name Service on a target Windows systems and forces the system to place its name in conflict so that the name can no longer be used. This essentially blocks the client from participating in the NetBIOS network and creates a network DoS for that system.

Start with a memorable phrase, such as "Maryhadalittlelamb"
Change every other character to uppercase, resulting in "MaRyHaDaLiTtLeLaMb"
Change a to @ and i to 1 to yield "M@RyH@D@L1TtLeL@Mb"
Drop every other pair to result in a secure repeatable password or "M@H@L1LeMb"

Now you have a password that meets all the requirements, yet can be "remade" if necessary.

PHoss: A Password Sniffer

"PHoss is a sniffer. A normal sniffer software is designed to find problems in data communication on the network. PHoss is designed to know some protocols which use (or may use) clear text passwords. Many protocols are designed to use secure authentication. For fallback they define a lowest level of authentication using clear text. Many companies use this lowest fallback definition as standard setting to make the product working in many environments." read more...

Download: http://www.phenoelit-us.org/phoss/download.html

More information

Web-fu - The Ultimate Web Hacking Chrome Extension

Web-fu Is a web hacking tool focused on discovering and exploiting web vulnerabilitites.

BROWSER INTEGRATION

This tool has many advantages, as a browser-embedded webhacking tool, is very useful for scanning browser-authenticated applications, if browser can authenticate and access to the web application, the tool also can. Note that some other tools do not support neither certificate authentication nor web vpn accesses.
The integration with chrome, provides a more comfortable and agile way of web-hacking, and you have all the application data loaded on the hacking tool, you don't need to copy the url, cookies, etc. to the tool, just right click and hack.
The browser rendering engine is also used in this tool, to draw the html of the responses.

FALSES POSITIVES

When I coded this tool, I was obsessed with false positives, which is the main problem in all detection tools. I have implemented a gauss algorithm, to reduce the faslse positives automatically which works very very well, and save a lot of time to the pentester.

VIDEO

Here is a video, with some of the web-fu functionalitites:

VISUAL FEATURES

This tool has a visual crawler. Normal crawlers doesn't parse the ajvascript, this tool does. The visual crawler loads each link of the web site, rendering the html and executing all the javascript as a normal load, then the links are processed from he DOM and clicked.
A visual form cracker, is also available, althow is experimental and only works on some kind of forms.

SCANNING FEATURES

The web-fu's portscanner, has a database of a common web ports, like 80,81,8080 and so on.
The cracker module, can bruteforce web directories to find new attack vectors, and can fuzz get and post parameters for discovering vulns, and also crack passwords. There are 9 preloaded wordlists, and you can also load a custom wordlist. Prefilters, falsepositive reductor and render will be helpful. The scanners support SSL, if the website can be loaded in the chrome, can be scanned by web-fu.

ENCODERS & DECODERS

The supported encoders and decoders are: base64, urlescape and urlencode

OTHER FEATURES

A web notepad is available, saving the information on the browser localStorage, there is one notepad per site. A cookie editor is also very useful for pentesting. The inteceptor, is like a web proxy but from the inside of the browser, you can intercept a request There is also a session locker and a exploit web search.

CHROME STORE
Here is the link to the chrome store, the prize is about one euro, very cheap if you compare with other scanners: Web-Fu on Chrome Store

With webfu, you will do the best web site pentest and vulnerability assessment.

Related posts

WHO IS ETHICAL HACKER

Who is hacker?
A hacker is a Creative person and a creative Programmer,who have knowledge about Networking,Operating system,hacking & a best creative social engineer who control anyone's mind he is also a knowledgeable person.

Hacker are the problem solver and tool builder.

A hacker is an individual who uses computer, networking and other skills to overcome a technical problem but it often refers to a person who uses his or her abilities to gain unauthorized access to system or networks in order to commit crimes.

Related word

PKCE: What Can(Not) Be Protected

This post is about PKCE [RFC7636], a protection mechanism for OAuth and OpenIDConnect designed for public clients to detect the authorization code interception attack.

At the beginning of our research, we wrongly believed that PKCE protects mobile and native apps from the so called „App Impersonation" attacks. Considering our ideas and after a short discussion with the authors of the PKCE specification, we found out that PKCE does not address this issue.

In other words, the protection of PKCE can be bypassed on public clients (mobile and native apps) by using a maliciously acting app.

OAuth Code Flow

In Figure 1, we briefly introduce how the OAuth flow works on mobile apps and show show the reason why we do need PKCE.
In our example the user has two apps installed on the mobile phone: an Honest App and an Evil App. We assume that the Evil App is able to register the same handler as the Honest App and thus intercept messages sent to the Honest App. If you are more interested in this issue, you can find more information here [1].

Figure 1: An example of the "authorization code interception" attack on mobile devices.

Step 1: A user starts the Honest App and initiates the authentication via OpenID Connect or the authorization via OAuth. Consequentially, the Honest App generates an Auth Request containing the OpenID Connect/OAuth parameters: client_id, state, redirect_uri, scope, authorization_grant, nonce, ….

Step 2: The Browser is called and the Auth Request is sent to the Authorization Server (usually Facebook, Google, …).

The Honest App could use a Web View browser. However, the current specification clearly advice to use the operating system's default browser and avoid the usage of Web Views [2]. In addition, Google does not allow the usage of Web View browser since August 2016 [3].

Step 3: We asume that the user is authenticated and he authorizes the access to the requested resources. As a result, the Auth Response containing the code is sent back to the browser.

Step 4: Now, the browser calls the Honest App registered handler. However, the Evil App is registered on this handler too and receives the code.

Step 5: The Evil App sends the stolen code to the Authorization Server and receives the corresponding access_token in step 6. Now, the Evil App can access the authorized ressources.

Optionally, in step 5 the App can authenticate on the Authorization Server via client_id, client_secret. Since, Apps are public clients they do not have any protection mechanisms regarding the storage of this information. Thus, an attacker can easy get this information and add it to the Evil App.

Proof Key for Code Exchange - PKCE (RFC 7636)

Now, let's see how PKCE does prevent the attack. The basic idea of PKCE is to bind the Auth Request in Step 1 to the code redemption in Step 5. In other words, only the app generated the Auth Request is able to redeem the generated code.

Figure 2: PKCE - RFC 7636

Step 1: The Auth Request is generated as previosly described. Additionally, two parameters are added:

The Honest App generates a random string called code_verifier
The Honest App computes the code_challenge=SHA-256(code_verifier)
The Honest App specifies the challenge_method=SHA256

Step 2: The Authorization Server receives the Auth Request and binds the code to the received code_challenge and challenge_method.

Later in Step 5, the Authorzation Server expects to receive the code_verifier. By comparing the SHA-256(code_verifier) value with the recieved code_challenge, the Authorization Server verifies that the sender of the Auth Request ist the same as the sender of the code.

Step 3-4: The code leaks again to the Evil App.

Step 5: Now, Evil App must send the code_verifier together with the code. Unfortunatelly, the App does not have it and is not able to compute it. Thus, it cannot redeem the code.

PKCE Bypass via App Impersonation

Again, PKCE binds the Auth Request to the coderedemption.

The question rises, if an Evil App can build its own Auth Request with its own code_verifier, code_challenge and challenge_method.The short answer is – yes, it can.

Figure 3: Bypassing PKCE via the App Impersonation attack

Step 1: The Evil App generates an Auth Request. The Auth Request contains the client_id and redirect_uri of the Honest App. Thus, the User and the Authorization Server cannot recognize that the Evil App initiates this request.

Step 2-4: These steps do not deviate from the previous description in Figure 2.

Step 5: In Step 5 the Evil App sends the code_verifier used for the computation of the code_challenge. Thus, the stolen code can be successfully redeemed and the Evil App receives the access_token and id_token.

OAuth 2.0 for Native Apps

The attack cannot be prevented by PKCE. However, the IETF working group is currently working on a Draft describing recommendations for using OAuth 2.0 for native apps.

References

[1] http://mews.sv.cmu.edu/papers/ccs-14.pdf

[2] https://tools.ietf.org/html/draft-ietf-oauth-native-apps-06#section-8.1

[3] https://developers.googleblog.com/2016/08/modernizing-oauth-interactions-in-native-apps.html

Authors

Vladislav Mladenov
Christian Mainka (@CheariX)

More info

Tuesday, April 14, 2020

Linux Command Line Hackery Series - Part 6

Welcome back to Linux Command Line Hackery series, I hope you've enjoyed this series so far and would have learned something (at least a bit). Today we're going to get into user management, that is we are going to learn commands that will help us add and remove users and groups. So bring it on...

Before we get into adding new users to our system lets first talk about a command that will be useful if you are a non-root user.

Command: sudo
Syntax: sudo [options] command
Description: sudo allows a permitted user to execute a command as a superuser or another user.

Since the commands to follow need root privileges, if you are not root then don't forget to prefix these commands with sudo command. And yes you'll need to enter the root password in order to execute any command with sudo as root.

Command: useradd
Syntax: useradd [options] username
Description: this command is used for creating new user but is kinda old school.
Lets try to add a new user to our box.
[Note: I'm performing these commands as root user, you'll need root privileges to add a new user to your box. If you aren't root then you can try these commands by prefixing the sudo command at the very beginning of these command like this sudo useradd joe. You'll be prompted for your root password, enter it and you're good to go]

useradd joe

To verify that this command has really added a user to our box we can look at three files that store a users data on a Linux box, which are:

/etc/passwd -> this file stores information about a user separated by colons in this manner, first is login name, then in past there used to be an encrypted password hash at the second place however since the password hashes were moved to shadow file now it has a cross (x) there, then there is user id, after it is the user's group id, following it is a comment field, then the next field contains users home directory, and at last is the login shell of the user.

/etc/group -> this file stores information about groups, that is id of the group and to which group an user belongs.

/etc/shadow -> this file stores the encrypted password of users.

Using our command line techniques we learned so far lets check out these files and verify if our user has been created:

cat /etc/passwd /etc/group /etc/shadow | grep joe

In the above screenshot you can notice an ! in the /etc/shadow, this means the password of this user has not been set yet. That means we have to set the password of user joe manually, lets do just that.

Command: passwd
Syntax: passwd [options] [username]
Description: this command is used to change the password of user accounts.
Note that this command needs root privileges. So if you are not root then prefix this command with sudo.

passwd joe

After typing this command, you'll be prompted password and then for verifying your password. The password won't show up on the terminal.
Now joe's account is up and running with a password.

The useradd command is a old school command, lets create a new user with a different command which is kinda interactive.

Command: adduser
Syntax: adduser [options] user
Description: adduser command adds a user to the system. It is more friendly front-end to the useradd command.

So lets create a new user with adduser.

adduser jane

as seen in the image it prompts for password, full name and many other things and thus is easy to use.

OK now we know how to create a user its time to create a group which is very easy.

Command: addgroup
Syntax: addgroup [options] groupname
Description: This command is used to create a new group or add an existing user to an existing group.

We create a new group like this

addgroup grownups

So now we have a group called grownups, you can verify it by looking at /etc/group file.
Since joe is not a grownup user yet but jane is we'll add jane to grownups group like this:

addgroup jane grownups

Now jane is the member of grownups.

Its time to learn how to remove a user from our system and how to remove a group from the system, lets get straight to that.

Command: deluser
Syntax: deluser [options] username
Description: remove a user from system.

Lets remove joe from our system

deluser joe

Yes its as easy as that. But remember by default deluser will remove the user without removing the home directory or any other files owned by the user. Removing the home directory can be achieved by using the --remove-home option.

deluser jane --remove-home

Also the --remove-all-files option removes all the files from the system owned by the user (better watch-out). And to create a backup of all the files before deleting use the --backup option.

We don't need grownups group so lets remove it.

Command: delgroup
Syntax: delgroup [options] groupname
Description: remove a group from the system.

To remove grownups group just type:

delgroup grownups

That's it for today hope you got something in your head.

Related word

Zirikatu Tool - Fud Payload Generator Script

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On Pins and Needles

Wednesday, April 15, 2020

CEH: System Hacking, Cracking A Password, Understanding The LAN Manager Hash, NetBIOS DoS Attacks

Cracking a Password

Understanding the LAN Manager Hash

Cracking Windows 2000 Passwords

Redirecting the SMB Logon to the Attacker

SMBRelay

SMBRelay2

pwdump2

Samdump

C2MYAZZ

NetBIOS DoS Attacks

Read more

PHoss: A Password Sniffer

More information

Web-fu - The Ultimate Web Hacking Chrome Extension

WHO IS ETHICAL HACKER

Related word

PKCE: What Can(Not) Be Protected

OAuth Code Flow

Proof Key for Code Exchange - PKCE (RFC 7636)

PKCE Bypass via App Impersonation

OAuth 2.0 for Native Apps

References

Authors

Tuesday, April 14, 2020

Linux Command Line Hackery Series - Part 6

Related word

Zirikatu Tool - Fud Payload Generator Script

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