Are you tired of reading endless news stories about ethical hacking and not really knowing what that means? Let's change that!
This Post is for the people that:
Have No Experience With Cybersecurity (Ethical Hacking)
Have Limited Experience.
Those That Just Can't Get A Break
OK, let's dive into the post and suggest some ways that you can get ahead in Cybersecurity.
I receive many messages on how to become a hacker. "I'm a beginner in hacking, how should I start?" or "I want to be able to hack my friend's Facebook account" are some of the more frequent queries. Hacking is a skill. And you must remember that if you want to learn hacking solely for the fun of hacking into your friend's Facebook account or email, things will not work out for you. You should decide to learn hacking because of your fascination for technology and your desire to be an expert in computer systems. Its time to change the color of your hat 😀
I've had my good share of Hats. Black, white or sometimes a blackish shade of grey. The darker it gets, the more fun you have.
If you have no experience don't worry. We ALL had to start somewhere, and we ALL needed help to get where we are today. No one is an island and no one is born with all the necessary skills. Period.OK, so you have zero experience and limited skills…my advice in this instance is that you teach yourself some absolute fundamentals.
Let's get this party started.
What is hacking?
Hacking is identifying weakness and vulnerabilities of some system and gaining access with it.
Hacker gets unauthorized access by targeting system while ethical hacker have an official permission in a lawful and legitimate manner to assess the security posture of a target system(s)
There's some types of hackers, a bit of "terminology". White hat — ethical hacker. Black hat — classical hacker, get unauthorized access. Grey hat — person who gets unauthorized access but reveals the weaknesses to the company. Script kiddie — person with no technical skills just used pre-made tools. Hacktivist — person who hacks for some idea and leaves some messages. For example strike against copyright.
We have been adding pcaps to the collection so remember to check out the folder ( Pcap collection) for the recent pcaps.
I had a project to test some malicious and exploit pcaps and collected a lot of them (almost 1000) from various public sources. You can see them in the PUBLIC folder. The credits go to the authors of the pcaps listed in the name of each file. Please visit their blogs and sites to see more information about the pcaps, see their recent posts, and send them thanks. The public pcaps have no passwords on them.
Update:Dec 13. 2014
Despite rare updates of this post, we have been adding pcaps to the collection so remember to check out the folder ( Pcap collection (New link)) for the recent pcaps!
Update:Dec 31. 2013 - added new pcaps
I did some spring cleaning yesterday and came up with these malware and exploit pcaps. Such pcaps are very useful for IDS and signature testing and development, general education, and malware identification. While there are some online public sandboxes offering pcaps for download like Cuckoo or Anubis but looking for them is a tedious task and you cannot be totally sure the pcap is for the malware family supposedly analysed - in other words, if the sandbox says it is Zeus does not necessarily mean that it is.
These are from identified and verified (to the best of my knowledge and belief - email me if you find errors) malware samples.
All of them show the first stage with the initial callback and most have the DNS requests as well. A few pcaps show extended malware runs (e.g. purplehaze pcap is over 500mb). Most pcaps are mine, a few are from online sandboxes, and one is borrowed from malware.dontneedcoffee.com. That said, I can probably find the corresponding samples for all that have MD5 listed if you really need them. Search contagio, some are posted with the samples.
Each file has the following naming convention: BIN [RTF, PDF] - the filetype of the dropper used, malware family name, MD5, and year+month of the malware analysis.
I will be adding more pcaps in the future. Please donate your pcaps from identified samples, I am sure many of you have.
All pcaps archives have the same password (same scheme), email me if you need it. I tried posting it without any passwords and pass infected but they get flagged as malware. Modern AV rips though zips and zips with the pass 'infected' with ease.
In part 1 and 2 we covered re-entrancy and authorization attack scenarios within the Ethereum smart contract environment. In this blog we will cover integer attacks against blockchain decentralized applications (DAPs) coded in Solidity.
Integer Attack Explanation:
An integer overflow and underflow happens when a check on a value is used with an unsigned integer, which either adds or subtracts beyond the limits the variable can hold. If you remember back to your computer science class each variable type can hold up to a certain value length. You will also remember some variable types only hold positive numbers while others hold positive and negative numbers.
If you go outside of the constraints of the number type you are using it may handle things in different ways such as an error condition or perhaps cutting the number off at the maximum or minimum value.
In the Solidity language for Ethereum when we reach values past what our variable can hold it in turn wraps back around to a number it understands. So for example if we have a variable that can only hold a 2 digit number when we hit 99 and go past it, we will end up with 00. Inversely if we had 00 and we subtracted 1 we would end up with 99.
Normally in your math class the following would be true:
99 + 1 = 100 00 - 1 = -1
In solidity with unsigned numbers the following is true: 99 + 1 = 00 00 - 1 = 99
So the issue lies with the assumption that a number will fail or provide a correct value in mathematical calculations when indeed it does not. So comparing a variable with a require statement is not sufficiently accurate after performing a mathematical operation that does not check for safe values.
That comparison may very well be comparing the output of an over/under flowed value and be completely meaningless. The Require statement may return true, but not based on the actual intended mathematical value. This in turn will lead to an action performed which is beneficial to the attacker for example checking a low value required for a funds validation but then receiving a very high value sent to the attacker after the initial check. Lets go through a few examples.
Simple Example:
Lets say we have the following Require check as an example: require(balance - withdraw_amount > 0) ;
Now the above statement seems reasonable, if the users balance minus the withdrawal amount is less than 0 then obviously they don't have the money for this transaction correct?
This transaction should fail and produce an error because not enough funds are held within the account for the transaction. But what if we have 5 dollars and we withdraw 6 dollars using the scenario above where we can hold 2 digits with an unsigned integer?
Let's do some math. 5 - 6 = 99
Last I checked 99 is greater than 0 which poses an interesting problem. Our check says we are good to go, but our account balance isn't large enough to cover the transaction. The check will pass because the underflow creates the wrong value which is greater than 0 and more funds then the user has will be transferred out of the account.
Because the following math returns true: require(99 > 0)
Withdraw Function Vulnerable to an UnderFlow:
The below example snippet of code illustrates a withdraw function with an underflow vulnerability:
In this example the require line checks that the balance is greater then 0 after subtracting the _amount but if the _amount is greater than the balance it will underflow to a value above 0 even though it should fail with a negative number as its true value.
require(balances[msg.sender] - _amount > 0);
It will then send the value of the _amount variable to the recipient without any further checks:
msg.sender.transfer(_amount);
Followed by possibly increasing the value of the senders account with an underflow condition even though it should have been reduced:
balances[msg.sender] -= _amount;
Depending how the Require check and transfer functions are coded the attacker may not lose any funds at all but be able to transfer out large sums of money to other accounts under his control simply by underflowing the require statements which checks the account balance before transferring funds each time.
Transfer Function Vulnerable to a Batch Overflow:
Overflow conditions often happen in situations where you are sending a batched amount of values to recipients. If you are doing an airdrop and have 200 users who are each receiving a large sum of tokens but you check the total sum of all users tokens against the total funds it may trigger an overflow. The logic would compare a smaller value to the total tokens and think you have enough to cover the transaction for example if your integer can only hold 5 digits in length or 00,000 what would happen in the below scenario?
You have 10,000 tokens in your account You are sending 200 users 499 tokens each Your total sent is 200*499 or 99,800
The above scenario would fail as it should since we have 10,000 tokens and want to send a total of 99,800. But what if we send 500 tokens each? Lets do some more math and see how that changes the outcome.
You have 10,000 tokens in your account You are sending 200 users 500 tokens each Your total sent is 200*500 or 100,000 New total is actually 0
This new scenario produces a total that is actually 0 even though each users amount is 500 tokens which may cause issues if a require statement is not handled with safe functions which stop an overflow of a require statement.
Lets take our new numbers and plug them into the below code and see what happens:
1: The total variable is 100,000 which becomes 0 due to the 5 digit limit overflow when a 6th digit is hit at 99,999 + 1 = 0. So total now becomes 0.
2: This line checks if the users balance is high enough to cover the total value to be sent which in this case is 0 so 10,000 is more then enough to cover a 0 total and this check passes due to the overflow.
3: This line deducts the total from the senders balance which does nothing since the total of 10,000 - 0 is 10,000. The sender has lost no funds.
4-5: This loop iterates over the 200 users who each get 500 tokens and updates the balances of each user individually using the real value of 500 as this does not trigger an overflow condition. Thus sending out 100,000 tokens without reducing the senders balance or triggering an error due to lack of funds. Essentially creating tokens out of thin air.
In this scenario the user retained all of their tokens but was able to distribute 100k tokens across 200 users regardless if they had the proper funds to do so.
Lab Follow Along Time:
We went through what might have been an overwhelming amount of concepts in this chapter regarding over/underflow scenarios now lets do an example lab in the video below to illustrate this point and get a little hands on experience reviewing, writing and exploiting smart contracts. Also note in the blockchain youtube playlist we cover the same concepts from above if you need to hear them rather then read them.
For this lab we will use the Remix browser environment with the current solidity version as of this writing 0.5.12. You can easily adjust the compiler version on Remix to this version as versions update and change frequently. https://remix.ethereum.org/
Below is a video going through coding your own vulnerable smart contract, the video following that goes through exploiting the code you create and the videos prior to that cover the concepts we covered above:
This next video walks through exploiting the code above, preferably hand coded by you into the remix environment. As the best way to learn is to code it yourself and understand each piece:
Conclusion:
We covered a lot of information at this point and the video series playlist associated with this blog series has additional information and walk throughs. Also other videos as always will be added to this playlist including fixing integer overflows in the code and attacking an actual live Decentralized Blockchain Application. So check out those videos as they are dropped and the current ones, sit back and watch and re-enforce the concepts you learned in this blog and in the previous lab. This is an example from a full set of labs as part of a more comprehensive exploitation course we have been working on.
Welcome back, hope you are enjoying this series, I don't know about you but I'm enjoying it a lot. This is part 3 of the series and in this article we're going to learn some new commands. Let's get started Command: w Syntax: w Function: This simple function is used to see who is currently logged in and what they are doing, that is, their processes. Command: whoami Syntax: whoami Function: This is another simple command which is used to print the user name associated with the current effective user ID. Try it and it will show up your user name. If you want to know information about a particular user no matter whether it is you or someone else there is a command for doing that as well. Command: finger Syntax: finger[option] [username] Function: finger is a user information lookup program. The [] around the arguments means that these arguments are optional this convention is used everywhere in this whole series. In order to find information about your current user you can simply type: fingerusername Here username is your current username. To find information about root you can type: finger root and it will display info about root user. Command: uname Syntax: uname[options] Function: uname is used to display information about the system. uname is mostly used with the flag -a, which means display all information like this: uname-a Command: df Syntax: df[option] [FILE ...] Function: df is used to display the amount of space available. If you type df in your terminal and then hit enter you'll see the used and available space of every drive currently mounted on the system. However the information is displayed in block-size, which is not so much human friendly. But don't worry we can have a human friendly output as well using df by typing: df-h the -h flag is used to display the used and available space in a more user friendly format. We can also view the info of a single drive by specifying the drive name after df like this: df-h /dev/sda2 That's it for now about df, let's move on. Command: free Syntax: free[options] Function: free is used to display the amount of free and used physical memory and swap memory in the system. Again the displayed information is in block-size to get a more human readable format use the -h flag like this: free-h Command: cal Syntax: cal[options] Function: cal stands for calendar. It is used to display the calendar. If you want to display current date on the calendar you can simply type: cal and wohooo! you get a nice looking calendar on screen with current date marked but what if you want to display calendar of a previous month well you can do that as well. Say you want to display calendar of Jan 2010, then you'll have to type: cal-d 2010-01 Nice little handy tool, isn't it?
Command: file Syntax: filefilename ... Function: file is an awesome tool, it's used to classify a file. It is used to determine the file type. Let's demonstrate the usage of this command by solving a Noob's CTF challenge using file and base64 commands. We'll talk about base64 command in a bit. Go to InfoSecInstitute CTF Website. What you need to do here is to save the broken image file on your local computer in your home directory. After saving the file open your terminal (if it isn't already). Move to your home directory and then check what type of file it is using the file command: cd fileimage.jpg Shocking output? The file command has identified the above file as an ASCII text file which means the above file is not an image file rather it is a text file now it's time to see it's contents so we'll type: catimage.jpg What is that? It's some kind of gibberish. Well it's base64 encoded text. We need to decode it. Let's learn how to do that. Command: base64 Syntax: base64[option] FILE ... Function: base64 command is used to encode/decode data and then print it to stdout. If we're to encode some text in base64 format we'd simply type base64 hit enter and then start typing the text in the terminal after you're done hit enter again and then press CTRL+D like this: base64 some text here <CTRL+D> c29tZSB0ZXh0IGhlcmUK# output - the encoded string But in the above CTF we've got base64 encoded data we need to decode it, how are we going to do that? It's simple: base64-d image.jpg There you go you've captured the flag. The-d flag here specifies that we want to decode instead of encode and after it is the name of file we want to decode. Voila! So now you're officially a Hacker! Sorry no certificates available here :) That's it for this article meet ya soon in the upcoming article.
VI Gestão Administrativa do Gabinete Regional da 6ª Oficialaria Executiva do Estado de Minas Gerais
MCR - Álvaro Luiz ("Alvinho")
MCRA - Bruno Tomé ("Cunil")
SEC - Matheus Jacó ("Jacó")
