The random() function of the smart contract implementation for CryptoSaga, an Ethereum game, generates a random value with publicly readable variables such as timestamp, the current block's blockhash, and a private variable (which can be read with a getStorageAt call). Therefore, attackers can precompute the random number and manipulate the game (e.g., get powerful characters or get critical damages).

References

• https://nvd.nist.gov/vuln/detail/CVE-2018-12975
• https://medium.com/@jonghyk.song/create-legendary-champs-by-breaking-prng-of-cryptosaga-an-ethereum-rpg-game-cve-2018-12975-8de733ff8255