တာ၀ရခ်စ္သူ

Note: We will start off our Smart Contract Hacking journey with some basic solidity programming in the first two weeks. After that we will ramp things up and get a little crazy deploying blockchains and liquidating funds from accounts. But since the purpose of this series is to share the information I have learned over the last two years. I do not want to alienate those new to Smart Contracts and programming so we will take these first few weeks a bit slow.

Also note the text was taken from a book I was / am writing, I retrofitted it for this blog, and placed videos where screenshots may otherwise exist. If something seems off.. Just DM me on twitter and I will update it anything I might have missed during editing, but I tried to edit it as best as possible to meet this format rather then a book.

Cheers @Fiction

http://cclabs.io

Thanks to @GarrGhar for helping me edit/sanity check info for each of the chapters.

About Solidity

The solidity programming language is the language used to write smart contracts on the Ethereum blockchain. As of my initial writing of this chapter the current compiler version was 0.6.6. However, the versions change rapidly. For example, when I started coding in solidity 2 years ago, solidity was in version 4 and now its version 7 with major library and coding stylistic requirement updates in version 5.

So, note that when compiling your code for labs its best to use the version sited in that particular example. This is easily achieved in the online compilers, by selecting the compiler version from the dropdown menu. If you would like to give yourself a small challenge, use the latest compiler version and try to modify the code to work with it. Usually this just requires a few minor modifications and can be a good learning experience under the hood of how Solidity works and what has changed.

Solidity is very similar to writing JavaScript and is fully object oriented. In the intro chapters we will attempt to provide a quick overview of solidity understanding needed for a penetration tester. This will not be full guide to programming, as programming is considered to be a pre-requisite to application hacking. Instead this chapter will be a gentle introduction of needed concepts you will use throughout this book. Solidity is also a needed pre-requisite for understanding the rest of the information and its associated exploitation course.

However, as long as you understand general programming concepts then you should have no trouble understanding solidity. It is a relatively easy language to get up and running with quickly in comparison to more mature languages like C++ and Java which may take a more significant amount of time to learn.

The most important thing to understand with solidity is that unlike traditional languages, solidity handles transactions of monetary value by default. Meaning you don't need to attach to a payment API to add transactions to your applications. Payment functionality is baked into the language as its primary purpose and for usage with the Ethereum blockchain. All that's needed for financial transactions in solidity is a standard library transfer function, and you can easily send value to anyone's public address.

For example, the following simple function will transfer a specified amount of Ether to the user calling the function provided they have a large enough balance to allow the transfer. But lets not dive into that just yet.

1.  function withdraw (uint amount) {

2.     require (amount <= balances[msg.sender]);

3.     msg.sender.transfer(amount);

4.  }

Structure of a Smart Contract

Rather than discuss payments at this point, let's not jump to far ahead of ourselves. We need to understand the structure of a smart contract. Let's take a look at a Hello World example. We will analyze all of the key aspects that make solidity different then other languages you may currently understand.

You can easily follow along with this on http://remix.ethereum.org which is a free online IDE and compiler for coding in solidity. A full video walk through of Remix is included later on in this chapter. Remix contains in-browser compilers and virtual environments that emulate block creation and allow you to send and receive transactions. This is a powerful development tool and absolutely free to use.

Below is the simple code example we will analyze before moving on to a live walk through.

1.  pragma solidity 0.6.6;

2.

3.  contract HelloWorld {

4.

5.     constructor () public payable {

6.           //This is a comment

7.           //You can put your configuration information here

8.     }

9.

10.   function hello () public pure returns (string memory) {

11.                  return "Hello World";

12.         }

13.}

There is a lot going on in this small program so I will try to break it down as simple as possible. In the first line, we have the pragma statement which is required at the top of each program to let the compiler know which version of solidity this code was written for. As I said earlier, these versions change rapidly due to the evolving technology and many changes are implemented into each new version. So, the compiler needs to know which version you intended this to run on.

On line 3 is the word "contract" followed by whatever name you wish to call your contract. The contract's functionality is then enclosed in curly braces. This is similar to creating a class in any other language. It's a block of associated code that can be inherited, or interfaced with and contains its own variables and methods.

On line 5 contained within the contract curly braces we have a constructor denoted by the word "constructor". The constructor is run one time at contract creation and used to setup any variables or details of the smart contract. This is often used for creating an administrator of the contract or other items that are needed prior to contract usage.

Functions and variables within Solidity also have various types and visibility set with their creation. In this case also on line 5 you will see the words "public" and "payable" used to describe the constructor.

Public you may be familiar with as it's a common visibility keyword used in other languages denoting that anyone can call this function. There are other visibility types in Solidity listed below, we will cover each of these in more detail as we use them to our advantage when hacking smart contracts:

Public

This allows anyone to call and use this function

Private

This allows only the current contract and its functions to call it directly.

Internal

This is similar to private except it also allows derived contracts to use its functionality

External

External can only be called externally by other contracts unless the "this" keyword is used with the function call.

The second keyword in the constructor definition "payable" you may not be familiar with unless you have worked on blockchain projects. The word payable within solidity is needed on any item that can receive Ether. So, by setting the constructor as payable we can send a base amount of Ether to the contract when its deployed. This will add an initial monetary liquidity for whatever functionality the contract is providing. For example, if this were a gambling game, we would need some initial Ethereum to payout our winners before our revenues catch up with our payouts and we start collecting large sums of failed gambling revenue.

Within the constructor is an example of how comments are handled in solidity, the simple double forward slash is used like in most languages. Comments function in the same way as any other language in that they are not processed and they are ignored by the compiler but are useful for understanding the code you wrote later after you have taking time apart from reading your code.

Finally, we have our simple hello function starting on line 10. Again, there is a lot going on here. First is the name of the function with parentheses that can contain arguments like in any other language. However, this function does not take arguments.

You will notice two more keywords in the function definition "pure" and "returns". Returns is simply the way the function denotes that it will return a value to the user, which it then states directly after it what type of variable it returns. In this case, it returns a string in memory. We will talk about memory and storage later on and the security implications of them.

Next is the word "Pure" there are a couple types of functions in Solidity which will list below with a brief description.

View

This type of function does not modify or change the state of the contract but may return values and use global variables.

Pure

A pure function is a function which is completely self-contained in that it only uses local variables and it does not change the state of the smart contract.

Finally, in line 11 we return our string to the user who called the function. In the context of a user, this could be a physical user using an application or smart contract functionality or it could actually be another smart contract calling the function.

Hands on Lab – Remix HelloWorld

Now that we talked over in detail all the new concepts to solidity programs using a small example, lets compile and run this code on remix.ethereum.org.

Action Steps:

ü Browse to remix.etherum.org
ü Type out the the code from above (Do not copy Paste it)
ü Compile and deploy the code
ü Review the transaction in the log window

Intro to the Remix Development Environment Video

In Remix create a new file and type out the example helloworld code. I would suggest that you actually type out all of the examples in this book. They will not be exhaustive or long and will provide you great value and make you comfortable when it comes to writing your own exploits and using the compilers and tools. These are all essential tools to your understanding.

Within your remix environment, you will want to select the compiler version 0.6.6 to ensure that this code runs correctly. If you typed out the code correctly you should not receive any errors and you will be able to deploy and interact with it. In the following video we will walk you through that process and explain some nuances of solidity.

Explaining and Compiling HelloWorld Video:

Lets now quickly review a few key points about the transaction that you saw within the video when compiling your code. This transaction is shown below.

__________________________________________________________________________________

call to HelloWorld.hello

CALL

from 0xBF8B5A94eD4dFB45089b455B1A0e296D6669c625

to HelloWorld.hello() 0xADe285e11e0B9eE35167d1E25C3605Eba1778C86

transaction cost 21863 gas (Cost only applies when called by a contract)

execution cost 591 gas (Cost only applies when called by a contract)

hash 0x14557f9552d454ca865deb422ebb50a853735b57efaebcfc9c9abe57ba1836ed

input 0x19f...f1d21

decoded input {}

decoded output {

"0": "string: Hello World"

}

logs []

_________________________________________________________________________________

The output above is a hello transaction which contains the relevant data retrieved when you executed the hello function in the video. The first important thing to notice is the word "CALL". In solidity there are call and send transactions. The difference between the two is whether they change the state of the blockchain or not. In this case we did not change the state, we only retrieved information so a CALL was issued. If we were changing variables and sending values then a SEND transaction would have been issued instead.

Next you will see the "From" address which should correspond with the address you used to call the transaction. The "To" field should be the address the smart contract was given when you deployed the smart contract. You can view this on your deployment screen next to the deployed contract name by hitting the copy button and pasting it somewhere to see the full value.

You will then see the costs and gas associated with the transaction. Costs change based on the size of the contracts and the assembly code created by the compiler. Each instruction has a cost. We will cover that later when we do a bit of debugging and decompiling.

Finally take note of the Decoded Output which contains the return string of "Hello World".

Summary

If you are new to solidity or new to programming in general this might have been a lot of information. In the next chapter we cover a few more key solidity concepts before moving on to exploiting vulnerabilities where a much more in depth understanding of how solidity works and its security implications will be explored. For more solidity resources and full-length free tutorials check out the following references

Homework:

https://cryptozombies.io/en/course/

Related news

Pokémon-themed Umbreon Linux Rootkit Hits x86, ARM Systems
Research: Trend Micro

There are two packages
one is 'found in the wild' full and a set of hashes from Trend Micro (all but one file are already in the full package)

Download

Download Email me if you need the password

File information

Part one (full package)

#	File Name	Hash Value	File Size (on Disk)	Duplicate?
1	.umbreon-ascii	0B880E0F447CD5B6A8D295EFE40AFA37	6085 bytes (5.94 KiB)
2	autoroot	1C5FAEEC3D8C50FAC589CD0ADD0765C7	281 bytes (281 bytes)
3	CHANGELOG	A1502129706BA19667F128B44D19DC3C	11 bytes (11 bytes)
4	cli.sh	C846143BDA087783B3DC6C244C2707DC	5682 bytes (5.55 KiB)
5	hideports	D41D8CD98F00B204E9800998ECF8427E	0 bytes ( bytes)	Yes, of file promptlog
6	install.sh	9DE30162E7A8F0279E19C2C30280FFF8	5634 bytes (5.5 KiB)
7	Makefile	0F5B1E70ADC867DD3A22CA62644007E5	797 bytes (797 bytes)
8	portchecker	006D162A0D0AA294C85214963A3D3145	113 bytes (113 bytes)
9	promptlog	D41D8CD98F00B204E9800998ECF8427E	0 bytes ( bytes)
10	readlink.c	42FC7D7E2F9147AB3C18B0C4316AD3D8	1357 bytes (1.33 KiB)
11	ReadMe.txt	B7172B364BF5FB8B5C30FF528F6C5125	2244 bytes (2.19 KiB)
12	setup	694FFF4D2623CA7BB8270F5124493F37	332 bytes (332 bytes)
13	spytty.sh	0AB776FA8A0FBED2EF26C9933C32E97C	1011 bytes (1011 bytes)	Yes, of file spytty.sh
14	umbreon.c	91706EF9717176DBB59A0F77FE95241C	1007 bytes (1007 bytes)
15	access.c	7C0A86A27B322E63C3C29121788998B8	713 bytes (713 bytes)
16	audit.c	A2B2812C80C93C9375BFB0D7BFCEFD5B	1434 bytes (1.4 KiB)
17	chown.c	FF9B679C7AB3F57CFBBB852A13A350B2	2870 bytes (2.8 KiB)
18	config.h	980DEE60956A916AFC9D2997043D4887	967 bytes (967 bytes)
19	config.h.dist	980DEE60956A916AFC9D2997043D4887	967 bytes (967 bytes)	Yes, of file config.h
20	dirs.c	46B20CC7DA2BDB9ECE65E36A4F987ABC	3639 bytes (3.55 KiB)
21	dlsym.c	796DA079CC7E4BD7F6293136604DC07B	4088 bytes (3.99 KiB)
22	exec.c	1935ED453FB83A0A538224AFAAC71B21	4033 bytes (3.94 KiB)
23	getpath.h	588603EF387EB617668B00EAFDAEA393	183 bytes (183 bytes)
24	getprocname.h	F5781A9E267ED849FD4D2F5F3DFB8077	805 bytes (805 bytes)
25	includes.h	F4797AE4B2D5B3B252E0456020F58E59	629 bytes (629 bytes)
26	kill.c	C4BD132FC2FFBC84EA5103ABE6DC023D	555 bytes (555 bytes)
27	links.c	898D73E1AC14DE657316F084AADA58A0	2274 bytes (2.22 KiB)
28	local-door.c	76FC3E9E2758BAF48E1E9B442DB98BF8	501 bytes (501 bytes)
29	lpcap.h	EA6822B23FE02041BE506ED1A182E5CB	1690 bytes (1.65 KiB)
30	maps.c	9BCD90BEA8D9F9F6270CF2017F9974E2	1100 bytes (1.07 KiB)
31	misc.h	1F9FCC5D84633931CDD77B32DB1D50D0	2728 bytes (2.66 KiB)
32	netstat.c	00CF3F7E7EA92E7A954282021DD72DC4	1113 bytes (1.09 KiB)
33	open.c	F7EE88A523AD2477FF8EC17C9DCD7C02	8594 bytes (8.39 KiB)
34	pam.c	7A947FDC0264947B2D293E1F4D69684A	2010 bytes (1.96 KiB)
35	pam_private.h	2C60F925842CEB42FFD639E7C763C7B0	12480 bytes (12.19 KiB)
36	pam_vprompt.c	017FB0F736A0BC65431A25E1A9D393FE	3826 bytes (3.74 KiB)
37	passwd.c	A0D183BBE86D05E3782B5B24E2C96413	2364 bytes (2.31 KiB)
38	pcap.c	FF911CA192B111BD0D9368AFACA03C46	1295 bytes (1.26 KiB)
39	procstat.c	7B14E97649CD767C256D4CD6E4F8D452	398 bytes (398 bytes)
40	procstatus.c	72ED74C03F4FAB0C1B801687BE200F06	3303 bytes (3.23 KiB)
41	readwrite.c	C068ED372DEAF8E87D0133EAC0A274A8	2710 bytes (2.65 KiB)
42	rename.c	C36BE9C01FEADE2EF4D5EA03BD2B3C05	535 bytes (535 bytes)
43	setgid.c	5C023259F2C244193BDA394E2C0B8313	667 bytes (667 bytes)
44	sha256.h	003D805D919B4EC621B800C6C239BAE0	545 bytes (545 bytes)
45	socket.c	348AEF06AFA259BFC4E943715DB5A00B	579 bytes (579 bytes)
46	stat.c	E510EE1F78BD349E02F47A7EB001B0E3	7627 bytes (7.45 KiB)
47	syslog.c	7CD3273E09A6C08451DD598A0F18B570	1497 bytes (1.46 KiB)
48	umbreon.h	F76CAC6D564DEACFC6319FA167375BA5	4316 bytes (4.21 KiB)
49	unhide-funcs.c	1A9F62B04319DA84EF71A1B091434C64	4729 bytes (4.62 KiB)
50	cryptpass.py	2EA92D6EC59D85474ED7A91C8518E7EC	192 bytes (192 bytes)
51	environment.sh	70F467FE218E128258D7356B7CE328F1	1086 bytes (1.06 KiB)
52	espeon-connect.sh	A574C885C450FCA048E79AD6937FED2E	247 bytes (247 bytes)
53	espeon-shell	9EEF7E7E3C1BEE2F8591A088244BE0CB	2167 bytes (2.12 KiB)
54	espeon.c	499FF5CF81C2624B0C3B0B7E9C6D980D	14899 bytes (14.55 KiB)
55	listen.sh	69DA525AEA227BE9E4B8D59ACFF4D717	209 bytes (209 bytes)
56	spytty.sh	0AB776FA8A0FBED2EF26C9933C32E97C	1011 bytes (1011 bytes)
57	ssh-hidden.sh	AE54F343FE974302F0D31776B72D0987	127 bytes (127 bytes)
58	unfuck.c	457B6E90C7FA42A7C46D464FBF1D68E2	384 bytes (384 bytes)
59	unhide-self.py	B982597CEB7274617F286CA80864F499	986 bytes (986 bytes)
60	listen.sh	F5BD197F34E3D0BD8EA28B182CCE7270	233 bytes (233 bytes)

part 2 (those listed in the Trend Micro article)

#	File Name	Hash Value	File Size (on Disk)
1	015a84eb1d18beb310e7aeeceab8b84776078935c45924b3a10aa884a93e28ac	A47E38464754289C0F4A55ED7BB55648	9375 bytes (9.16 KiB)
2	0751cf716ea9bc18e78eb2a82cc9ea0cac73d70a7a74c91740c95312c8a9d53a	F9BA2429EAE5471ACDE820102C5B8159	7512 bytes (7.34 KiB)
3	0a4d5ffb1407d409a55f1aed5c5286d4f31fe17bc99eabff64aa1498c5482a5f	0AB776FA8A0FBED2EF26C9933C32E97C	1011 bytes (1011 bytes)
4	0ce8c09bb6ce433fb8b388c369d7491953cf9bb5426a7bee752150118616d8ff	B982597CEB7274617F286CA80864F499	986 bytes (986 bytes)
5	122417853c1eb1868e429cacc499ef75cfc018b87da87b1f61bff53e9b8e8670	9EEF7E7E3C1BEE2F8591A088244BE0CB	2167 bytes (2.12 KiB)
6	409c90ecd56e9abcb9f290063ec7783ecbe125c321af3f8ba5dcbde6e15ac64a	B4746BB5E697F23A5842ABCAED36C914	6149 bytes (6 KiB)
7	4fc4b5dab105e03f03ba3ec301bab9e2d37f17a431dee7f2e5a8dfadcca4c234	D0D97899131C29B3EC9AE89A6D49A23E	65160 bytes (63.63 KiB)
8	8752d16e32a611763eee97da6528734751153ac1699c4693c84b6e9e4fb08784	E7E82D29DFB1FC484ED277C702187818	55564 bytes (54.26 KiB)
9	991179b6ba7d4aeabdf463118e4a2984276401368f4ab842ad8a5b8b73088522	2B1863ACDC0068ED5D50590CF792DF05	7664 bytes (7.48 KiB)
10	a378b85f8f41de164832d27ebf7006370c1fb8eda23bb09a3586ed29b5dbdddf	A977F68C59040E40A822C384D1CEDEB6	176 bytes (176 bytes)
11	aa24deb830a2b1aa694e580c5efb24f979d6c5d861b56354a6acb1ad0cf9809b	DF320ED7EE6CCF9F979AEFE451877FFC	26 bytes (26 bytes)
12	acfb014304b6f2cff00c668a9a2a3a9cbb6f24db6d074a8914dd69b43afa4525	84D552B5D22E40BDA23E6587B1BC532D	6852 bytes (6.69 KiB)
13	c80d19f6f3372f4cc6e75ae1af54e8727b54b51aaf2794fedd3a1aa463140480	087DD79515D37F7ADA78FF5793A42B7B	11184 bytes (10.92 KiB)
14	e9bce46584acbf59a779d1565687964991d7033d63c06bddabcfc4375c5f1853	BBEB18C0C3E038747C78FCAB3E0444E3	71940 bytes (70.25 KiB)

တာ၀ရခ်စ္သူ

Sunday, August 30, 2020

Smart Contract Hacking Chapter 1 - Solidity For Penetration Testers Part 1 (Hello World)

About Solidity

Structure of a Smart Contract

Hands on Lab – Remix HelloWorld

Action Steps:

Summary

Homework:

Related news

Rootkit Umbreon / Umreon - X86, ARM Samples

More info

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