A lottery smart contract implementation for Greedy 599, an Ethereum gambling game, generates a random value that is predictable via an external contract call. The developer used the extcodesize() function to prevent a malicious contract from being called, but the attacker can bypass it by writing the core code in the constructor of their exploit code. Therefore, it allows attackers to always win and get rewards.

References

• https://nvd.nist.gov/vuln/detail/CVE-2018-17877
• https://github.com/TEAM-C4B/CVE-LIST/tree/master/CVE-2018-17877