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Friday, September 25, 2020

Exploring World of Smart Contracts with MadMax

 A space we have now looked at for some time, a somewhat technical example well worth going through.   Note close attention to 'vulnerabilities' which remain at disturbing levels. 

MadMax: Analyzing the Out-of-Gas World of Smart Contracts

By Neville Grech, Michael Kong, Anton Jurisevic, Lexi Brent, Bernhard Scholz, Yannis Smaragdakis  Communications of the ACM, October 2020, Vol. 63 No. 10, Pages 87-95   10.1145/3416262

Ethereum is a distributed blockchain platform, serving as an ecosystem for smart contracts: full-fledged intercommunicating programs that capture the transaction logic of an account. A gas limit caps the execution of an Ethereum smart contract: instructions, when executed, consume gas, and the execution proceeds as long as gas is available.

Gas-focused vulnerabilities permit an attacker to force key contract functionality to run out of gas—effectively performing a permanent denial-of-service attack on the contract. Such vulnerabilities are among the hardest for programmers to protect against, as out-of-gas behavior may be uncommon in nonattack scenarios and reasoning about these vulnerabilities is nontrivial.

In this paper, we identify gas-focused vulnerabilities and present MadMax: a static program analysis technique that automatically detects gas-focused vulnerabilities with very high confidence. MadMax combines a smart contract decompiler and semantic queries in Datalog. Our approach captures high-level program modeling concepts (such as "dynamic data structure storage" and "safely resumable loops") and delivers high precision and scalability. MadMax analyzes the entirety of smart contracts in the Ethereum blockchain in just 10 hours and flags vulnerabilities in contracts with a monetary value in billions of dollars. Manual inspection of a sample of flagged contracts shows that 81% of the sampled warnings do indeed lead to vulnerabilities.  ... '  

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