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Over/Under Flows
Invisible Cheatsheet:
- balances[msg.sender] = 0
- _amount = 1
- Difference = 2**256 - 1](https://image.slidesharecdn.com/attacks-181012095051/85/Attacks-on-Smart-Contracts-63-320.jpg)
Uploaded byMarcin Majchrzak
Attacks on Smart Contracts
The document discusses various aspects of Ethereum smart contracts, including notable security vulnerabilities and attacks on the network, such as the DAO hack and parity wallet breaches. It provides insights into coding practices, prevention strategies, and tools for auditing and testing smart contracts. Additionally, it highlights the necessity of thorough testing and monitoring to prevent exploits in blockchain technologies.
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Attacks on Smart Contracts
- 1. General enough textthat is displayed usually on the first slide
- 2. Attacks by Marcin Majchrzak onSmart Contracts
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- 4. Cheats Invisible Cheatsheet: - Thisslide is empty - You can not see it - But I can ♥
- 5. Disclaimer Mainly on Eth % //%% ///%%% ////%%%% /////%%%%% //////%%%%%% ///////%%%%%%% ////////%%%%%%%% /////////%%%%%%%%% //////////%%%%%%%%%% ///////////%%%%%%%%%%% ////////////%%%%%%%%%%%% ///////////%%&@@%%%%%%%%%% ////////%%%%%%&@@@@@@%%%%%%% /////%%%%%%%%%%&@@@@@@@@@@%%%% /%%%%%%%%%%%%%%%&@@@@@@@@@@@@@@% /%%%%%%%%%%%%%%%%&@@@@@@@@@@@@@@@@ %%%%%%%%%%%%%%%%%&@@@@@@@@@@@@@@@@@ %%%%%%%%%%%%%&@@@@@@@@@@@@@ /%%%%%%%%%&@@@@@@@@@ % /// %%%%%%&@@@@@@ %%% ////// %%%&@@@ %%%%%% /////// * %%%%%%% ///////// %%%%%%%%% ///////////#%%%%%%%%%%% /////////#%%%%%%%%% ////////#%%%%%%%% ///////#%%%%%%% /////#%%%%% ////#%%%% //#%% /#%
- 6. The Scale ofAttacks Hacker stole 3.6 million Ether ($50 million) - DAO Hacker stole 150k Ether ($30 million) - Parity Attackers stole 50k Ether ($7 million) - Coindash Attackers stole $8.4 million in tokens - Veritaseum Thief stole 25k Ether ($13 million) - Bancor Millions
- 7. About Ethereum If youknow the enemy and know yourself, you will win a hundred of battles. Sun Tzu, The Art of War
- 8. Solidity About Ethereum Invisible Cheatsheet: -Statically typed - Inheritance - C++, Python, JS
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- 10. About Ethereum Assembly PUSH1 0x60 PUSH10x40 MSTORE PUSH1 0x04 CALLDATASIZE LT PUSH2 0x02a5 JUMPI PUSH4 0xffffffff PUSH1 0xe0 PUSH1 0x02 EXP PUSH1 0x00 CALLDATALOAD DIV AND PUSH4 0x01ffc9a7 DUP2 EQ PUSH2 0x02dd JUMPI DUP1 PUSH4 0x0519ce79 EQ PUSH2 0x0329Invisible Cheatsheet: - Opcodes
- 11. About Ethereum Disassembly PUSH1 0x60 PUSH10x40 MSTORE PUSH1 0x04 CALLDATASIZE LT PUSH2 0x02a5 JUMPI PUSH4 0xffffffff PUSH1 0xe0 PUSH1 0x02 EXP PUSH1 0x00 CALLDATALOAD DIV AND PUSH4 0x01ffc9a7 DUP2 EQ PUSH2 0x02dd JUMPI DUP1 PUSH4 0x0519ce79 EQ PUSH2 0x0329 Invisible Cheatsheet: - EVMDis - Binary Ninja - Searching for Vulns
- 12. About Ethereum EVM PUSH1 0x60 PUSH10x40 MSTORE PUSH1 0x04 CALLDATASIZE LT PUSH2 0x02a5 JUMPI PUSH4 0xffffffff PUSH1 0xe0 PUSH1 0x02 EXP PUSH1 0x00 CALLDATALOAD DIV AND PUSH4 0x01ffc9a7 DUP2 EQ PUSH2 0x02dd JUMPI DUP1 PUSH4 0x0519ce79 EQ PUSH2 0x0329 Invisible Cheatsheet: - Too broad - Stack - Memory - Storage
- 13. About Ethereum Blockchain PUSH1 0x60 PUSH10x40 MSTORE PUSH1 0x04 CALLDATASIZE LT PUSH2 0x02a5 JUMPI PUSH4 0xffffffff PUSH1 0xe0 PUSH1 0x02 EXP PUSH1 0x00 CALLDATALOAD DIV AND PUSH4 0x01ffc9a7 DUP2 EQ PUSH2 0x02dd JUMPI DUP1 PUSH4 0x0519ce79 EQ PUSH2 0x0329 Invisible Cheatsheet: - Too broad - Running EVM - Transactions
- 14. About Ethereum Transaction Invisible Cheatsheet: -Code in data - Input to contracts
- 15. About Ethereum Python implementations Client:https://github.com/ ethereum/pyethapp Core: https://github.com/ ethereum/pyethereum VM: https://github.com/ ethereum/py-evm
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- 17. Biggest Attacks 17 June2006 - the attacker drained 3.5M ETH (~$50M) from the DAO smart contract, collected in an ICO a month earlier. The DAO hack occurred after the token sale had already ended. The DAO Attack happened due to a recursive calling vulnerability. The attacker withdrew Ether from The DAO smart contract multiple times using the same DAO Tokens. Facts The DAO has 663 lines of code. Statistics show, that there are up to 15–50 bugs per 1000 lines of code. Although extensive testing and auditing can significantly reduce this number, it is very hard to bring it down to 0.
- 18. Biggest Attacks The DAO ActualCode Invisible Cheatsheet: - Calc funds - Send funds - Event - Update last
- 19. Biggest Attacks The DAO Simplified InvisibleCheatsheet: - Calc funds - Send funds - Update last
- 20. Biggest Attacks The DAO Attacker InvisibleCheatsheet: - Interface - Withdraw - Fallback
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- 28. Biggest Attacks The DAO Prevention InvisibleCheatsheet: - Guard counter - Code execution - Comparing counter
- 29. Biggest Attacks The DAO Example InvisibleCheatsheet: - Modifier - Calc funds - Send funds - Update
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- 31. Biggest Attacks The DAO Flow AttackerVictim Invisible Cheatsheet: - localCounter = 1 - _guardCounter = 1
- 32. Biggest Attacks The DAO Flow AttackerVictim Invisible Cheatsheet: - localCounter = 1 - _guardCounter = 1 Invisible Cheatsheet: - localCounter = 2 - _guardCounter = 2
- 33. Biggest Attacks The DAO Flow AttackerVictim Invisible Cheatsheet: - localCounter = 1 - _guardCounter = 1 Invisible Cheatsheet: - localCounter = 2 - _guardCounter = 2
- 34. Biggest Attacks The DAO Flow AttackerVictim Invisible Cheatsheet: - localCounter = 1 - _guardCounter = 1 Invisible Cheatsheet: - localCounter = 2 - _guardCounter = 2
- 35. Biggest Attacks The DAO Flow AttackerVictim Invisible Cheatsheet: - localCounter = 1 - _guardCounter = 1 Invisible Cheatsheet: - localCounter = 2 - _guardCounter = 2
- 36. Biggest Attacks The DAO Flow AttackerVictim Invisible Cheatsheet: - localCounter = 1 - _guardCounter = 1 Invisible Cheatsheet: - localCounter = 2 - _guardCounter = 2 Invisible Cheatsheet: - localCounter = 2 - _guardCounter = 3
- 37. Biggest Attacks The DAO Afterthe DAO Hard Fork Invisible Cheatsheet: - Recover DAO funds - Partially agree - Partially disagree - Division
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- 39. Biggest Attacks 19 July2017 - bug found in the multi-signature wallet code used as part of Parity Wallet software was exploited and 150k ETH (~$30M) was stolen. Parity 6 November 2017 - vulnerability in the smart contract code was exploited and more than 500k ETH (~$150M) was frozen. Facts 5 June 2018 - 3rd security alert had place for Parity regarding potential consensus issue. However this time there were no casualties.
- 40. Biggest Attacks Actual Code Parity InvisibleCheatsheet: - Library init - Library kill - Wallet lib ref - Wallet fallback - No visibility on init
- 41. Biggest Attacks Simplified Parity Invisible Cheatsheet: -How Lib work - In general
- 42. Biggest Attacks Delegate Call Parity InvisibleCheatsheet: - isOwner
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- 44. Biggest Attacks Delegate Call+ Fallback Parity Invisible Cheatsheet: - Combo attack
- 45. Biggest Attacks Freezing Funds Parity InvisibleCheatsheet: - Accidentally - Playing - Learning
- 46. Biggest Attacks Parity Meme “I accidentallykilled it” - devops199 ¯_(ツ)_/¯
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- 48. Biggest Attacks Prevention Careful withDelegate Call Careful with Fallback Avoid combination of both Parity
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- 50. Funny Attacks King ofthe Ether The “King of the Ether Throne” is a game where players compete for acquiring the title of “King of the Ether”. Facts If someone wishes to be the king, he must pay some ether to the current king, plus a small fee to the contract.
- 51. King of theEther Actual Code Funny Attacks Invisible Cheatsheet: - Simple enough - King - Fallback - Send Ether blindly
- 52. Attacker Invisible Cheatsheet: - Interface -Withdraw - Fallback - Not payable - Code (2300 gas) - Using transfer fails King of the Ether Funny Attacks
- 53. Bug Unchecked Low LevelCalls King of the Ether Funny Attacks
- 54. Prevention Do not trustReceiver Remember about default 2300 gas User transfer or check send result King of the Ether Funny Attacks
- 55. Constructors are specialfunctions which often perform critical, privileged tasks when initialising contracts. Rubixi Before solidity v0.4.22 constructors were defined as functions that had the same name as the contract that contained them. Facts Funny Attacks
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- 58. Rubixi Bug Access Control Funny Attacks InvisibleCheatsheet: - Same in Parity
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- 61. More Exploits Block Manipulation InvisibleCheatsheet: - now == block.timestamp - Miner abusements
- 62. More Exploits Front Running HonestUserfinds solution. HonestUser sends transaction with default gas fee. Attacker listens for HonestUser transaction. Attacker sends copy of HonestUser transaction with higher gas fee. Invisible Cheatsheet: - Mining races
- 63. More Exploits Over/Under Flows InvisibleCheatsheet: - balances[msg.sender] = 0 - _amount = 1 - Difference = 2**256 - 1
- 64. Old Exploits Call DepthAttack Call depth attack makes an external call to fail because it exceeds the maximum call stack of 1024. Invisible Cheatsheet: - Issues handling exceptions - It is solved
- 65. Old Exploits Call DepthAttack https://github.com/ ethereum/EIPs/ blob/master/ EIPS/eip-150.md
- 66. Prepare for Failure Philosophy InvisibleCheatsheet: - Circuit breaker - Rate limiting - Upgradable for bugfixes
- 67. Roll out carefully Philosophy InvisibleCheatsheet: - Test test test - Coverage - Testnet - Bug bounties - Roll out in phases (beta) - Volume testing
- 68. Keep contracts simple Philosophy InvisibleCheatsheet: - Modularize - Use already written tools - Clarity > Performance - KISS
- 69. Stay up todate Philosophy Invisible Cheatsheet: - Upgradable (antipattern) - Registry - Monitor your tools
- 70. Be aware of blockchainproperties Philosophy Invisible Cheatsheet: - Understand visibility - Be careful about external calls - Remember about gas
- 71. Be aware of blockchainproperties Philosophy Invisible Cheatsheet: - Understand visibility - Be careful about external calls - Remember about gas
- 72. Recommendations Avoid external calls InvisibleCheatsheet: - Call - Send - Transfer
- 73. Recommendations Favour pull over push Invisible Cheatsheet: - Push -Pull - Non-reentrant
- 74. Recommendations Beware the Math InvisibleCheatsheet: - Float does not exist
- 75. Patterns Guard Check OracleRandomness Access Restriction Pull over Push Proxy Delegate https://fravoll.github.io/ solidity-patterns
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- 77. Security Tools https://consensys.github.io/ smart-contract-best-practices/security_tools/ EVMDis FSolidMSmartCheck Security Mythril Remix
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- 79. Some cool links ReversingContracts https://arvanaghi.com/blog/ reversing-ethereum-smart-contracts/ Smashing Smart Contracts https://www.youtube.com/ watch?v=iqf6epACgds Colored inspection of Smart Contracts https://arxiv.org/pdf/1807.01868.pdf DASP - Top 10 Vulnerabilities https://dasp.co/
- 80. Thank you Invisible Cheatsheet: -We made it ♥ - 80 slides - Check time