Signum Node: Integer overflow in SMART_FEES fee distribution allows arbitrary miner reward inflation

Signum Node is a HDD-mined cryptocurrency using an energy efficient and fair Proof-of-Commitment (PoC+) consensus algorithm. Prior to version 3.9.9, an integer overflow in BlockServiceImpl.applyBlock() allowed a miner to receive an arbitrarily inflated block reward by crafting a block with a negative totalFeeCashBackNqt value. The vulnerability was introduced when the SMART_FEES hardfork (block ~1,029,000) enabled fee cash-back and burn accounting without overflow protection. This issue has been patched in version 3.9.9.