Sereum: Protecting Existing Smart Contracts Against Re-Entrancy Attacks (1812.05934v1)

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 run-time overhead. As a by-product, we develop three advanced re-entrancy attacks to demonstrate the limitations of existing offline vulnerability analysis tools.

• The paper introduces Sereum, a runtime security layer that employs dynamic taint-tracking to prevent re-entrancy attacks without altering existing contracts.
• The paper demonstrates Sereum's effectiveness by mitigating advanced re-entrancy attack types with only a 0.06% false-positive rate and a 9.6% runtime overhead.
• The paper outlines a dual deployment strategy, allowing Sereum to function as both a live security enhancement on the blockchain and a diagnostic tool for developers.

Security in Ethereum Smart Contracts: An Exploration of Sereum

The paper "Sereum: Protecting Existing Smart Contracts Against Re-Entrancy Attacks" addresses critical vulnerabilities in smart contracts, chiefly focusing on the notorious re-entrancy attacks as epitomized by the DAO incident. These types of attacks exploit the rarity of inconsistent internal state executions during re-entrancy, thereby allowing an adversary to interact maliciously with a smart contract beyond the intended transaction scope. The research presents Sereum, a security layer built into the Ethereum Virtual Machine (EVM) for run-time protection without requiring modifications to existing contracts, offering an innovative solution to a long-standing problem.

Key Contributions and Methodology

Sereum introduces a dynamic taint-tracking mechanism that identifies and locks state variables engaged in control-flow decisions. By tracing these variables, Sereum effectively prevents state changes during re-entrant function calls unless flagged and verified. This runtime protection ensures a clear demarcation of dangerous states, thereby reducing the risk of exploit via consistent state monitoring within the transaction stack.

Furthermore, the research delineates three novel forms of advanced re-entrancy attacks: cross-function, delegated, and create-based re-entrancy. Sereum’s runtime analysis overcomes limitations inherent in static analysis tools by dynamically monitoring contracts during execution. This substantial development underscores dynamic taint tracking as applied within a practical smart contract execution context.

Evaluation and Results

In assessing Sereum's efficacy, approximately 80 million Ethereum transactions were re-executed, highlighting Sereum's capacity to thwart previously undetectable attack patterns with a minimal false-positive rate of 0.06% and a nominal runtime overhead of 9.6%. This level of coverage underscores the practical deployment potential of Sereum shielding legacy contracts from re-entrancy vulnerabilities, an area previously elusive to offline static analysis tools due to their inherent limitations concerning semantic knowledge of contracts.

Implications and Future Work

Sereum’s design introduces a robust framework adaptable into the Ethereum ecosystem to fortify against re-entrancy breaches. For practitioners, the integration strategy discussed provides a dual mode of deployment: as a live security layer within the blockchain environment and as a diagnostic tool for developers wishing to preemptively secure their contracts. This hybrid approach marries theoretical robustness with practical applicability, advancing the dialogue on best practices within the domain significantly.

Potential future research could delve into the scalability of Sereum’s integration across varying blockchain platforms and evaluate cross-platform vulnerabilities. Additionally, developing methods to streamline smart contract upgrading while maintaining backwards compatibility offers fertile ground for exploration. Technical improvements in detecting further nuanced patterns of attack can extend Sereum’s utility beyond its current re-entrancy paradigm.

Conclusion

The Sereum framework embodies a pivotal step forward in the secure execution of smart contracts on Ethereum, specifically targeting re-entrancy vulnerabilities often overlooked or poorly mitigated by contemporary solutions. By championing dynamic analysis and integrating efficiently within existing EVM implementations, Sereum presents a comprehensive strategy to preemptively protect against re-entrancy attacks, heralding an era of improved resilience onto the Ethereum blockchain. This work invites researchers and developers alike to explore the intricate layers of smart contract security with renewed vigor and intent.