CVE-2018-14715 in Cryptogs
Summary
by MITRE
The endCoinFlip function and throwSlammer function of the smart contract implementations for Cryptogs, an Ethereum game, generate random numbers with an old block's hash. Therefore, attackers can predict the random number and always win the game.
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Analysis
by VulDB Data Team • 03/13/2020
The vulnerability identified in CVE-2018-14715 affects the Cryptogs Ethereum-based gaming platform where the endCoinFlip and throwSlammer smart contract functions utilize block hashes from previous blocks to generate random numbers. This represents a fundamental flaw in cryptographic randomness implementation that directly impacts the integrity of the game mechanics. The use of historical block hashes for random number generation creates predictable outcomes that can be exploited by malicious actors. According to CWE-330, this vulnerability stems from the use of insufficiently random values in security-critical applications, specifically in the context of blockchain-based gambling systems where randomness is paramount for fair play.
The technical implementation flaw occurs because Ethereum block hashes are deterministic and known in advance to anyone who can observe the blockchain. When smart contracts reference older block hashes for random number generation, attackers can pre-compute the expected outcomes by simply querying the blockchain for the relevant block data. This vulnerability operates at the intersection of smart contract development practices and cryptographic security principles, where the assumption that block hashes provide sufficient entropy proves incorrect. The attack vector is particularly dangerous because it requires no direct interaction with the smart contract itself, as the randomness is predictable from external observation of the blockchain state.
The operational impact of this vulnerability extends beyond simple game manipulation to represent a broader security failure in blockchain-based gaming applications. Players who understand the vulnerability can consistently win games by calculating the expected random outcomes before the contract execution occurs. This undermines the fundamental trust model of decentralized applications and demonstrates how seemingly innocuous design decisions can create exploitable weaknesses. The vulnerability aligns with ATT&CK technique T1059.006 for smart contract manipulation and represents a classic example of how insufficient entropy in cryptographic implementations can compromise entire systems. The predictable nature of the outcomes means that attackers can systematically exploit this weakness to gain unfair advantages in the game's economic mechanisms.
Mitigation strategies for this vulnerability require fundamental changes to the smart contract architecture and random number generation methods. Developers must implement proper entropy sources such as combining multiple unpredictable variables, utilizing oracles with external randomness, or employing cryptographic techniques that ensure true randomness. The solution should incorporate principles from NIST SP 800-90B for randomness validation and avoid reliance on block-based entropy. Additionally, the implementation should follow established best practices for secure smart contract development as outlined in the Ethereum Smart Contract Best Practices guidelines. Regular security audits and formal verification processes should be implemented to identify similar weaknesses in other contract functions that might rely on predictable data sources for generating randomness.