Sereum: Protecting Existing Smart Contracts Against Re-Entrancy Attacks

Abstract

Recently, a number of existing blockchain systems have witnessed major bugs and vulnerabilities within smart contracts. Although the literature features a number of proposals for securing smart contracts, these proposals mostly focus on proving the correctness or absence of a certain type of vulnerability within a contract, but cannot protect deployed (legacy) contracts from being exploited. In this paper, we address this problem in the context of re-entrancy exploits and propose a novel smart contract security technology, dubbed Sereum (Secure Ethereum), which protects existing, deployed contracts against re-entrancy attacks in a backwards compatible way based on run-time monitoring and validation. Sereum does neither require any modification nor any semantic knowledge of existing contracts. By means of implementation and evaluation using the Ethereum blockchain, we show that Sereum covers the actual execution flow of a smart contract to accurately detect and prevent attacks with a false positive rate as small as 0.06% and with negligible runtime overhead. As a by-product, we develop three advanced reentrancy attacks to demonstrate the limitations of existing offline vulnerability analysis tools.

Detecting nondeterministic payment bugs in Ethereum smart contracts

“…This research aims to present a practical tool to detect bugs from online contracts in bytecode format. Our tool roots the same assumption with previous techniques [Luu et al 2016;Nikolić et al 2018;Rodler et al 2018;Tsankov et al 2018] that aim to find bugs rather than rigorous verification, which would come with its own set of challenges, such as the typical lack of nontrivial and complete contract-specific properties.…”

“…Some other research, including MADMAX, which focuses on a set of gas-focused vulnerabilities associated with denial-of-service attack [Grech et al 2018], and TeEther [Krupp and Rossow 2018], which synthesizes exploitation towards online contracts, is orthogonal to our work. In addition, some runtime monitoring techniques enforce data-flow integrity to defeat reentrancy attacks [Rodler et al 2018]. We also notice a line of research work verifying smart contracts with formal methods [Amani et al 2018;Bhargavan et al 2016;Grishchenko et al 2018;Hildenbrandt et al 2018;Hirai 2017].…”

“…The initiating cause of EO bugs is the nondeterministic scheduling as well. There could exist even tricker reentrancy attack vectors by crossing different contracts [Rodler et al 2018]. For instance, EVM enables łcontract delegationž for a contract to outsource its global storage and computations to some online library contracts with common reusable functionalities.…”

“…In addition, a contract is allowed to create another contract, where the constructor function of the newly-created contract is called for initialization. However, a newly-created contract could perform (malicious) reentrancy by redirecting the execution flow from its constructor to functions of its creator [Rodler et al 2018]. As studied in recent research, such cross-contract reentrancy attacks can impede existing static bug detectors, because it is not feasible to analyze individual contracts to reveal such hidden defects.…”

“…Meanwhile, abnormal behaviors are monitored during online execution by instrumenting the Ethereum Virtual Machine (EVM). Most of these existing approaches utilize appropriate predefined vulnerability patterns which can only be found by experts [ConsenSys 2018;Jiang et al 2018;Kalra et al 2018;Luu et al 2016;Rodler et al 2018;Tsankov et al 2018]. Hence, our capability of finding defects and identifying contract vulnerabilities is limited by the currently known patterns.…”