QA-06: Unchecked Subtraction in Emptying Transaction Threshold Can Underflow

Summary

The emptying-transaction threshold subtracts 1 from execution_delay without guarding the case where execution_delay == 0.

Vulnerability details

1
let blocks_since_latest_txn = SeqNum(
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    block_seq_num_of_curr_txn
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        .0
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        .saturating_sub(balance_state.block_seqnum_of_latest_txn.0),
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);
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!balance_state.is_delegated && blocks_since_latest_txn > execution_delay - SeqNum(1)

Impact

Because SeqNum subtraction panics on underflow, a zero execution delay can crash the path on an otherwise valid block.

Recommendation

Rewrite the comparison so it does not rely on execution_delay - 1, or clamp the minimum allowed delay at construction time.