Xarva

Smart Contract Audit Report

Executive Summary

This report presents the outcomes of our collaborative engagement with the Xarva team, focusing on the comprehensive evaluation of the Xarva, rXRV, IUSDT, PaymentSettler, and BillSubscriptionManager contracts.

Our team conducted an initial security assessment from November 18th to November 25th, 2024 using code from the project team's GitHub repository. This report was updated on December 3rd, 2024 to reflect changes from commit bb1fe8 to commit c310740.

Xarva is a new platform which facilitates billing and payment between users who are subscribed.

Audit Scope

Audit Findings

All findings have been resolved or acknowledged, though some centralized aspects are present.

if (!xrvToken.transfer(bill.merchant, protocolFeeXRV)) {
	revert CompensationToBillingEntityFailed();
}
if (!xrvToken.transfer(billSettler, protocolFeeXRV)) {
	revert CompensationToPayingEntityFailed();
}

if (merchant.subscriptionTier > receiver.subscriptionTier) revert ReceiverSubscriptionPlanIsHigherThanYours();

if (billRaiser.subscriptionTier > settler.subscriptionTier) revert PlanTierIsLowerThanPaymentReceiverMerchant();

if (merchant.subscriptionTier < receiver.subscriptionTier) revert ReceiverSubscriptionPlanIsHigherThanYours();

IBillSubscriptionManager.Merchant memory billRaiser = subscriptionBillManager.getMerchant(bill.merchant);
IBillSubscriptionManager.Merchant memory settler = subscriptionBillManager.getMerchant(bill.merchant);
if (billRaiser.subscriptionTier > settler.subscriptionTier) revert PlanTierIsLowerThanPaymentReceiverMerchant();

uint256 remainingTime = merchant.endAt - block.timestamp;
uint256 remainingDays;

remainingDays = remainingTime / 1 days;

remainingDays = (remainingTime / 1 days) + 1;

System Overview

Tokens

The Xarva contract introduces Xarva (XRV) as a token used for bill payments within the platform. Upon deployment, the owner is minted the initial supply of XRV tokens. The owner retains the ability to mint additional XRV tokens to themselves at any time and can also burn their tokens if desired. Ownership of the contract can be transferred at any time.

rXRV, or RewardXRV, is a new token used as a reward mechanism within the PaymentSettler contract. The Settler Role, initially assigned to the PaymentSettler contract upon deployment, can mint or burn rXRV tokens from any address. The Default Admin role, which is granted to the owner upon deployment, holds authority over role management. The Default Admin can grant or revoke the Settler Role for any address. Additionally, the owner can update the PaymentSettler address, assigning the Settler Role to the new address while revoking it from the previous one.

The IUSDT contract introduces Internal USDT, a token utilized for bill payouts within the platform. Similar to rXRV, the Settler Role, assigned to the PaymentSettler contract upon deployment, has the ability to mint or burn IUSDT tokens from any address. The Default Admin role, assigned to the owner upon deployment, oversees role management and can grant or revoke the Settler Role for any address. The owner also has the authority to update the PaymentSettler address, transferring the Settler Role to a new address and revoking it from the old one.

Subscriptions and Payments

This PaymentSettler contract allows users to settle bills if the bill's payment token is set to either "IUSDT" or XRV. Both the settler and the merchant must have valid subscriptions for a bill to be settled. Additionally, the bill amount must not exceed the maximum single bill settlement limit defined by the merchant's subscription tier, and the merchant's total payments received in a day must remain within their tier's daily settlement threshold. The bill amount is converted into XRV using the contract's current XRV price. The project team must ensure that the XRV price is constantly updated to avoid arbitrage using bill payments, as users can receive stablecoins based on the current XRV price.

When settling a bill, a protocol fee is applied to the bill amount. This fee is added to the amount transferred from the settler and also deducted from the payment received by the merchant. The collected XRV fee is sent to the BillSubscriptionManager's payment address. The total XRV amount, including the fee, is transferred from the user regardless of the original payment type. The merchant receives the bill amount minus the fee, either minted as IUSDT tokens or transferred in XRV. If the merchant receives IUSDT, the equivalent value in XRV is sent to the BillSubscriptionManager's payment address. At the end of the settlement, the protocol fee amount taken is returned back to the bill's merchant and recipient. As protocol fee was already transferred to the BillSubscriptionManager's payment address, the team must ensure that the contract is funded by sufficient XRV to facilitate this payment.

Once settled, the bill is marked as paid in the BillSubscriptionManager contract. Both the settler and the merchant are rewarded with rXRV tokens based on the settler reward and bill raiser reward percentages, respectively. These rewards become claimable after the settler and raiser vesting periods have elapsed. Users can swap their rXRV or IUSDT tokens for the stable token used by the BillSubscriptionManager, typically USDT, at a 1:1 ratio while the contract is active. During a swap, the user's rXRV or IUSDT is burned, and the equivalent amount in USDT is transferred to them, provided the contract holds a sufficient stable token balance.

The XRV price can be updated by the Price Updater address and remains valid for the defined price validity period. Bills can only be settled when there is an unexpired XRV price. The contract owner has extensive administrative control, including updating the XRV, rXRV, IUSDT, BillSubscriptionManager, and Price Updater addresses. The owner can also adjust the protocol fee percentage, settler and raiser reward percentages, vesting periods, and price validity period. Additionally, the owner can pause the contract, disabling bill settlements, reward claims, and token swaps. At any time, the owner can withdraw any XRV held by the contract.

This contract enables users to manage their subscriptions on the platform. Users can purchase a subscription for a specified tier for any number of months, paying in the contract's designated stable token. The subscription cost is determined by the tier's price and the duration purchased. Price changes may apply for multi-month purchases based on the tier's discount percentage. Alternatively, users can claim a one-time subscription to the free trial tier, which is valid for the designated free trial period. Users may also upgrade an existing subscription by paying the price difference between their current tier and the desired one for the remaining duration of the subscription.

The contract allows users to create bills specifying a recipient, amount, and payment token type, provided that both the merchant and recipient hold valid subscriptions. Additional conditions include the recipient having a subscription tier equal to or lower than the merchant, the bill amount being below the tier's maximum single bill limit, and the merchant’s total daily bills not exceeding the tier’s daily permitted amount. Created bills can be settled by the recipient through the PaymentSettler contract, while bill creators can delete unsettled bills if desired.

The contract owner holds various administrative privileges. They can update subscription tiers, including the daily limit, monthly price, multi-month discount, and maximum single bill amount. The free trial period can also be adjusted to a maximum of 30 days. Additionally, the owner can modify the addresses of the payment processor and stable token. The project team must ensure that only stable tokens with 6 decimals are used if they desire to keep a 1:1 ratio between rXRV, IUSDT, and the stable token. The contract can be paused by the owner, which disables user and admin subscription purchases and upgrades, bill creation and deletion, and bill settlements. The owner also has the authority to grant a subscription of any length to a user for any tier at no cost, provided the user does not already have an active subscription, or can upgrade a user's subscription at no cost.

Vulnerability Analysis

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What is a SourceHat Audit?

Typically, a smart contract audit is a comprehensive review process designed to discover logical errors, security vulnerabilities, and optimization opportunities within code. A SourceHat Audit takes this a step further by verifying economic logic to ensure the stability of smart contracts and highlighting privileged functionality to create a report that is easy to understand for developers and community members alike.

How Do I Interpret the Findings?

Each of our Findings will be labeled with a Severity level. We always recommend the team resolve High, Medium, and Low severity findings prior to deploying the code to the mainnet. Here is a breakdown on what each Severity level means for the project:

• High severity indicates that the issue puts a large number of users' funds at risk and has a high probability of exploitation, or the smart contract contains serious logical issues which can prevent the code from operating as intended.
• Medium severity issues are those which place at least some users' funds at risk and has a medium to high probability of exploitation.
• Low severity issues have a relatively minor risk association; these issues have a low probability of occurring or may have a minimal impact.
• Informational issues pose no immediate risk, but inform the project team of opportunities for gas optimizations and following smart contract security best practices.

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