Description

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.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.5",
  "pubDate": "2026-09-03T16:17:24.330Z",
  "pubdate": "2026-09-03T16:17:24.330Z",
  "executiveSummary": "The Signum Node cryptocurrency software contains an integer overflow vulnerability within its block processing logic. Identified in versions prior to 3.9.9, this flaw originates from inadequate input validation within the SMART_FEES hardfork implementation, which introduced fee cash-back and burn mechanics. An unauthenticated attacker capable of submitting a block to the network can exploit this flaw to bypass financial integrity checks. By crafting a block containing a negative 'totalFeeCashBackNqt' value, a miner can trigger an integer overflow that results in the generation of an arbitrarily inflated block reward. This vulnerability poses a critical risk to the economic stability of the Signum network, as it allows for the illicit creation of currency and the subversion of the Proof-of-Commitment (PoC+) consensus mechanism. The attack requires the ability to propagate a block on the network, which is inherent to the role of a mining node. Successful exploitation effectively enables the attacker to corrupt the ledger state and extract excessive rewards beyond the protocol-defined parameters. Immediate migration to version 3.9.9 or later is mandatory to ensure the integrity of the blockchain and the accuracy of reward distribution.",
  "technicalDetails": "The vulnerability is located in the BlockServiceImpl.applyBlock() function, which is responsible for processing and validating blocks within the Signum Node core. The flaw was introduced during the SMART_FEES hardfork, which brought architectural changes to how fees are processed, specifically regarding the accounting of fee cash-backs and burns.\nThe root cause is an integer overflow condition occurring during the calculation of block rewards. The system failed to enforce strict bounds checking on the 'totalFeeCashBackNqt' field within a block header or block body metadata. Because the code did not perform pre-condition validation to ensure that the value provided was non-negative and within acceptable mathematical limits, it permitted the processing of a negative integer.\nIn the context of standard blockchain accounting, these values are expected to be positive. When a negative value is passed to the arithmetic operations within applyBlock(), the underlying integer representation can wrap around or lead to incorrect summation results when combined with other reward components. By manipulating this specific field, an attacker causes the block reward calculation logic to produce an overflowed result that is significantly larger than intended by the protocol.\nThe attack flow follows these steps: 1. The attacker prepares a block candidate to be submitted to the network. 2. The attacker modifies the 'totalFeeCashBackNqt' parameter to a negative value chosen to trigger the overflow during reward computation. 3. The attacker broadcasts the crafted block to the network. 4. Vulnerable Signum Nodes receiving this block execute BlockServiceImpl.applyBlock(), which fails to validate the negative input. 5. The function calculates the reward, resulting in an inflated value due to the overflow. 6. The node incorporates the invalid, inflated reward into the chain, effectively minting unauthorized currency.\nThe vulnerability affects versions prior to 3.9.9. Because the logic is handled at the protocol layer, this does not require a traditional user-level exploit but rather a protocol-level abuse of the consensus rules. The lack of overflow protection or input sanitization allows the attacker to leverage the node's own validation logic against the security of the ledger. Post-exploitation, the attacker possesses the inflated reward, causing a permanent divergence in the supply accounting of the Signum cryptocurrency."
}