Griefing (e.g. no profit motive for an attacker, but damage to the users or the protocol)
Description
Brief/Intro
The calculation of the mint_amount in the current implementation of the claim_delay_mint can be truncated to zero if the numerator= (delay_mint_stake× get_x_algo_circulating_supply) is less than the denominator the current algo_balance, this leading to total loss of value especially by small stakes this is possible since the algo_balance can increase over time due to the rewards while the x_algo_citculating_supply remains constant,
Vulnerability Details
This is the current implented functionality it doesn't check for zero-value mint amount and this can lead to loss of value, also the mint_amount is integer type variables and cannot store floating values
@router.method(no_op=CallConfig.CALL)
def claim_delayed_mint(receiver: abi.Address, nonce: abi.StaticBytes[L[2]]) -> Expr:
box_name = Concat(DelayMintBox.NAME_PREFIX, receiver.get(), nonce.get())
box = BoxGet(box_name)
delay_mint_receiver = Extract(box.value(), DelayMintBox.RECEIVER, Int(32))
delay_mint_stake = ExtractUint64(box.value(), DelayMintBox.STAKE)
delay_mint_round = ExtractUint64(box.value(), DelayMintBox.ROUND)
algo_balance = ScratchVar(TealType.uint64)
mint_amount = ScratchVar(TealType.uint64)
return Seq(
# callable by anyone
rekey_and_close_to_check(),
# ensure initialised
Assert(App.globalGet(initialised_key)),
# check nonce is 2 bytes
Assert(Len(nonce.get()) == Int(2)),
# check box
box,
Assert(box.hasValue()),
Assert(receiver.get() == delay_mint_receiver),
Assert(Global.round() >= delay_mint_round),
# update total stake and total rewards
App.globalPut(total_pending_stake_key, App.globalGet(total_pending_stake_key) - delay_mint_stake),
App.globalPut(total_active_stake_key, App.globalGet(total_active_stake_key) + delay_mint_stake),
update_total_rewards_and_unclaimed_fees(),
# calculate mint amount
algo_balance.store(
App.globalGet(total_active_stake_key)
+ App.globalGet(total_rewards_key)
- delay_mint_stake
- App.globalGet(total_unclaimed_fees_key)
),
mint_amount.store(
If(
algo_balance.load(),
mul_scale(delay_mint_stake, get_x_algo_circulating_supply(), algo_balance.load()),
delay_mint_stake
)
),
# send xALGO to user
mint_x_algo(mint_amount.load(), receiver.get()),
# delete box so cannot claim multiple times
Assert(BoxDelete(box_name)),
# give box min balance to sender as incentive
InnerTxnBuilder.Begin(),
get_transfer_inner_txn(Global.current_application_address(), Txn.sender(), get_app_algo_balance(), Int(0)),
InnerTxnBuilder.Submit(),
# log so can retrieve info for claiming
Log(Concat(
MethodSignature("ClaimDelayedMint(byte[36],address,uint64,uint64)"),
box_name,
receiver.get(),
Itob(delay_mint_stake),
Itob(mint_amount.load()),
)),
)
The code can be resolved by adding the following line :
Assert(mint_amount.load())
This ensure that the execution is reverted for zero amount mint_value to ensure that value are not loss by users most especially small stakers, since the box that contains the minting details is deleted afterwards
Impact details
Likelihood: Moderate (it occurs most times when staked values are small). Impact: High it results in complete loss of stake for affected users
Resolution
Another implementation is to set a minimum value on the amount that can be staked in the implementation of the delay_mint functionality to prevent users from staking very small values.
Proof of Concept
Proof of Concept
# Example values
delay_mint_stake = 100
x_algo_circulating_supply = 10000000000
algo_balance = 1000000000001
# Calculate the mint_amount
numerator = delay_mint_stake * x_algo_circulating_supply
denominator = algo_balance
# Perform the integer division (mimicking the truncation behavior in PyTeal)
mint_amount = numerator // denominator
# Print the results
print(f"Numerator: {numerator}")
print(f"Denominator: {denominator}")
print(f"Calculated mint_amount (before truncation): {numerator / denominator}")
print(f"mint_amount (after truncation): {mint_amount}")
# Check the result
if mint_amount == 0:
print("The mint_amount was truncated to 0, causing a loss of the stake.")
else:
print("mint_amount is valid and greater than zero.")
