EIP712 signatures can be replayed in case of hard fork
Summary
If there is ever a hardfork for Beanstalk then EIP712 domainSeparator value will become invalid. This is because the chainId parameter is cached in constants. This means even after hard fork chainId would remain same which is incorrect and could cause possible replay attacks in 3 different parts of protocol: Tractor, Silo deposit approval, internal token approval.
Vulnerability Details
In "Relevant GitHub Links" section I referred 3 places where protocol uses constant chainId.
This means even after hard fork, EIP712 domain separator value will remain same and point to incorrect chainId.
Impact
After hard fork EIP712 signatures can be replayed on different chain.
Tools Used
Manual Review
Recommendations
Fetch chainId from current block instead of using constant
Lead Judging Commences
Replay attack in case of hard fork - Hardcoded chainId 712
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