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The Frey protocol is acting as a utility tool for a game project. In the game, multiple material tokens are generated through the Frey protocol, which requires the consumption of a certain number of material tokens. Since the whole game mechanics is unknown and out of scope, the underlying logic of token mint/burn/change operations in the Frey protocol is not clear, especially the function `task_do()` in the contract `Farmersworld`.

Financial models

Based on the EIP-721 standard (https://eips.ethereum.org/EIPS/eip-721), every ERC-721 compliant contract must implement the ERC721 and ERC165 interfaces. However, the current contract `ERC721` does not implement the ERC165 interface.

Non-standard `ERC721` contract

There should always be events emitted in the sensitive functions that are controlled by centralization roles.

For example:
- contract `Farmer_ERC721`: `base()`, `token_info_change()`, 
- contract `Farmersworld`: `coin_creat()`, `nft_creat()`, `task_type_creat()`, `task_creat()`, `task_do()`, `task_cancel()`.

Missing emit events

The linked variables(`FW_creat`) assigned in the constructor can be declared as `immutable`. Immutable state variables can be assigned during contract creation but will remain constant throughout the lifetime of a deployed contract. A big advantage of immutable variables is that reading them is significantly cheaper than reading from regular state variables since they will not be stored in storage.

Variables that could be declared as immutable

The contract has unlocked compiler version. An unlocked compiler version in the source code of the contract permits the user to compile it at or above a particular version. This, in turn, leads to differences in the generated bytecode between compilations due to different compiler versions. This can lead to an ambiguity when debugging as compiler specific bugs may occur in the codebase that would be hard to identify over a span of multiple compiler versions rather than a specific one.

Unlocked Compiler Version

`public` functions that are never called by the contract could be declared as `external`. `external` functions are more efficient than `public` functions.

Improper usage of `public` and `external` type

In the contract `Farmer_ERC721` the role `FW_creat` has authority over the functions shown in the diagram below.

Any compromise to the `FW_creat` account may allow the hacker to take advantage of this authority and users' assets may suffer loss.

![](https://accelerator-tasks-prod.s3.amazonaws.com/f5cac34b18684833b5faed92605001bc/diagrams/centralization-Farmer_ERC721-FW_creat.svg)

In the contract `Farmer_ERC721` the role `_owner` has authority over the functions shown in the diagram below.

Any compromise to the `_owner` account may allow the hacker to take advantage of this authority and users' assets may suffer loss.

![](https://accelerator-tasks-prod.s3.amazonaws.com/f5cac34b18684833b5faed92605001bc/diagrams/centralization-Farmer_ERC721-_owner.svg)

Centralization Risk in Farmer_ERC721.sol

In the contract `Farmer_ERC20` the role `FW_creat` has authority over the functions shown in the diagram below.

Any compromise to the `FW_creat` account may allow the hacker to take advantage of this authority and users' assets may suffer loss.

![](https://accelerator-tasks-prod.s3.amazonaws.com/f5cac34b18684833b5faed92605001bc/diagrams/centralization-Farmer_ERC20-FW_creat.svg)

In the contract `Farmer_ERC20` the role `_owner` has authority over the functions shown in the diagram below.

Any compromise to the `_owner` account may allow the hacker to take advantage of this authority, mint unexpected amount of tokens to arbitrary address and burn the tokens owned by any addresses.

![](https://accelerator-tasks-prod.s3.amazonaws.com/f5cac34b18684833b5faed92605001bc/diagrams/centralization-Farmer_ERC20-_owner.svg)

Centralization Risk in Farmer_ERC20.sol

In the contract `Farmersworld` the role `_owner` has the authority over the following function:

- function `coin_creat()`: create a new `Farmer_ERC20` token and add it to the `token_infos` struct,
- function `nft_creat()`: create a new `Farmer_ERC721` token and add it to the `token_infos` struct,
- function `task_type_creat()`: add a new type to the `token_infos` struct and `task_type` array,
- function `task_creat()`: add a new task to the `token_infos` struct and `nft_tasks` mapping,
- function `task_cancel()`: remove a task from the `token_infos` struct.

Any compromise to the `_owner` account may allow the hacker to take advantage of this authority and users' assets may suffer loss.

Centralization risk in 0126Farmersworld.sol

The function `task_do()` will execute all the tasks in the struct `task_infos`, including minting and burning tokens. However, the completed tasks are neither not removed from the struct `task_infos` nor marked as completed. The function is public with no restriction, so anybody can call it. As a result, malicious users can call this function multiple times to mint arbitrary amount of tokens.

Same tasks can be performed multiple times

The function `task_do()` will execute all the tasks in the struct `task_infos` with a single transaction. Thus, if one of the tasks fails, all the tasks will not be executed.

Complex batch function

The given input is missing the check for the non-zero address.

For example:
- contract `ERC20`: `sender` and `recipient` in function `_transfer()`, `account` in function `_mint()`, `account` in function `_burn()`, `owner` and `spender` in function `_approve()`,
- contract `ERC721`: `to` in function `_mint()`, `from` and `to` in function `_transfer()`,
- contract `Farmer_ERC20`: `newOwner` in function `setOwner()`, 
- contract `Farmer_ERC721`: `newOwner` in function `setOwner()`.

Missing input validation

In the contract `HE3Token` the role `_owner` has the authority over the following function:

- function `renounceOwnership()`: set the `owner` of current contract to `address(0)`,
- function `transferOwnership()`: transfer the `owner` role to any arbitrary addresses,
- function `mint()`: mint arbitrary amount of `HE3Token` to an arbitrary address `account`.

Also, the contract deployer has the authority over the following function:

- function `constructor()`: set the `owner` of current contract to the contract deployer and mint initial `HE3Token` (254000000 `HE3Token` to `initor` and 46000000 `HE3Token` to `pool`).

Any compromise to the `_owner` and the contract deployer account may allow the hacker to take advantage of this authority and users' assets may suffer loss.

Centralization risk in HE3Token.sol

In the contract `Ownable`， the role `_owner` has the authority over the following function:

- function `transferOwnership()`: transfer the `owner` role to any arbitrary addresses.

Any compromise to the `_owner` account may allow the hacker to take advantage of this authority and users' assets may suffer loss.

FREY

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