Balance Guard

Overview

This policy makes sure that a the balance of some address in some token (Native or ERC20) doesn't change over an allowed threshold with any given transaction.

Protected Attack Vector

If an attacker gains privileged access to an account (wallet or smart contract) - either by stealing the private keys or by exploiting some vulnerability - and the account has some balance in some token (Native or ERC20) - this policy will block a malicious transaction from going through if the change in balance is above a configured threshold for the token.

How It Works

1. When a transaction reaches this policy in the Pre Execution hook, it first looks up the balances of the account in it's configured tokens.

2. Then, in the Post Execution hook, the policy compares the difference in balance (per token) against it's configured change-threshold.

3. If the transaction changed the balance more than is allowed by the threshold, it will be reverted.

Setup Instructions

1. Deploy your own version of this policy (see Source Code).

2. Call the setConsumerMaxBalanceChange() method to configure the balance change thresholds.

3. Add the newly deployed policy to the Firewall (you can do this Globally or Per-Method, see Policy Administration).

4. That's it!

Properties

Name	Type	Description
consumerMaxBalanceChange	mapping (address => mapping (address => uint) )	a mapping between accounts, tokens, and their balance balance change threshold for example: [someAccount][someToken] = 50000
consumerLastBalance	mapping (address => mapping (address => uint[]) )	a mapping between accounts, tokens, and their balances before executing the transaction

Methods

setConsumerMaxBalanceChange()

function setConsumerMaxBalanceChange(address consumer, address token, uint maxBalanceChange)

Callable only by the policy owner. Sets the maximum balance change that can take place on the given token in a transaction.

Parameter Name	Type	Description
consumer	address	the account holding the balance
token	address	the token to track balance changes for
maxBalanceChange	uint	the maximum balance change for the token

removeToken()

function removeToken(address consumer, address token)

Callable only by the policy owner. Removes the token from the consumer, so that the policy will no longer track balance changes on that token.

Parameter Name	Type	Description
consumer	address	the account holding the balance
token	address	the token to track balance changes for

View Functions

getConsumerTokens()

function getConsumerTokens(address consumer)

Gets the tokens and their configured balance change threshold for consumer.

Parameter Name	Type	Description
consumer	address	the account holding the balance

Security Lifecycle

This policy runs during both the Firewall's Pre Execution and the Post Execution hooks.

Source Code

On our GitHub repository: BalanceChangePolicy.sol