fix: F-2026-18200 | [Dual Defense] Variable-Length Signer Addresses Enable Universal Executor Module Impersonation

app/ante/account_init_decorator.go

@@ -1,6 +1,7 @@
 package ante
 
 import (
+	"bytes"
 	"fmt"
 
 	sdk "github.com/cosmos/cosmos-sdk/types"
@@ -12,6 +13,7 @@ import (
 	codectypes "github.com/cosmos/cosmos-sdk/codec/types"
 	sdkerrors "github.com/cosmos/cosmos-sdk/types/errors"
 	"github.com/cosmos/cosmos-sdk/types/tx/signing"
+	"github.com/cosmos/cosmos-sdk/x/auth/ante"
 	authsigning "github.com/cosmos/cosmos-sdk/x/auth/signing"
 	txpolicy "github.com/pushchain/push-chain-node/app/txpolicy"
 )
@@ -55,7 +57,7 @@ func (aid AccountInitDecorator) AnteHandle(ctx sdk.Context, tx sdk.Tx, simulate
 			"address", sdk.AccAddress(newAccAddr).String(),
 			"simulate", simulate,
 		)
-		// if account does not exist on chain, bypass rest of ante chain (especially gas and signature verification) here.
+		// if account does not exist on chain, bypass rest of ante chain here.
 		// Perform signature verification on account number e and sequence number e instead.
 		if err := aid.verifySignatureForNewAccount(ctx, tx, simulate); err != nil {
 			ctx.Logger().Debug("account init decorator: signature verification failed for new account",
@@ -103,13 +105,52 @@ func (aid AccountInitDecorator) verifySignatureForNewAccount(ctx sdk.Context, tx
 		return errorsmod.Wrapf(sdkerrors.ErrUnauthorized, "invalid number of signer;  expected: %d, got %d", len(signers), len(sigs))
 	}
 
-	newAccAddr := sdk.AccAddress(signers[0])
+	params := aid.ak.GetParams(ctx)
+
+	// Enforce the signature count limit before doing any verification work.
+	// This decorator short-circuits the ante chain for new accounts, so
+	// ante.ValidateSigCountDecorator never runs for them; without this hard cap
+	// a gasless tx could carry an arbitrarily large multisig key and force the
+	// node to verify every sub-signature. Gas is deliberately NOT consumed here:
+	// gasless txs skip fee deduction entirely, so charging gas would cost an
+	// attacker nothing - the count cap is what actually bounds the work.
+	sigCount := 0
 	for _, sig := range sigs {
+		if sig.PubKey == nil {
+			return errorsmod.Wrap(sdkerrors.ErrInvalidPubKey, "pubkey is not provided in signature")
+		}
+		sigCount += ante.CountSubKeys(sig.PubKey)
+		if uint64(sigCount) > params.TxSigLimit {
+			return errorsmod.Wrapf(sdkerrors.ErrTooManySignatures,
+				"signatures: %d, limit: %d", sigCount, params.TxSigLimit)
+		}
+	}
+
+	newAccAddr := sdk.AccAddress(signers[0])
+	for i, sig := range sigs {
 		pubKey := sig.PubKey
 		if pubKey == nil {
 			return errorsmod.Wrap(sdkerrors.ErrInvalidPubKey, "pubkey is not provided in signature")
 		}
 
+		// Bind the declared signer to the key that actually signed the tx.
+		//
+		// VerifySignature below only proves "this key signed this tx"; it says
+		// nothing about WHO the tx claims to be from. Because this decorator
+		// short-circuits the ante chain for new accounts, the SDK's
+		// SetPubKeyDecorator - which owns this check - never runs, so a tx could
+		// declare an arbitrary signer while being signed by an unrelated key.
+		// Bech32 account addresses may be up to 255 bytes, and downstream
+		// conversion to a 20-byte EVM address keeps only the rightmost bytes, so
+		// a crafted longer signer could alias a module address.
+		//
+		// Guards mirror x/auth/ante/sigverify.go exactly so simulation and gas
+		// estimation keep working.
+		if !simulate && ctx.IsSigverifyTx() && !bytes.Equal(pubKey.Address().Bytes(), signers[i]) {
+			return errorsmod.Wrapf(sdkerrors.ErrInvalidPubKey,
+				"pubKey does not match signer address %s with signer index: %d", sdk.AccAddress(signers[i]).String(), i)
+		}
+
 		// retrieve signer data
 		chainID := ctx.ChainID()
 		var accSequence uint64 = 0

app/ante/account_init_signer_binding_test.go

@@ -0,0 +1,298 @@
+package ante_test
+
+import (
+	"context"
+	"fmt"
+	"testing"
+
+	kmultisig "github.com/cosmos/cosmos-sdk/crypto/keys/multisig"
+	"github.com/cosmos/cosmos-sdk/crypto/keys/secp256k1"
+	cryptotypes "github.com/cosmos/cosmos-sdk/crypto/types"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	sdkerrors "github.com/cosmos/cosmos-sdk/types/errors"
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/stretchr/testify/require"
+
+	clienttx "github.com/cosmos/cosmos-sdk/client/tx"
+	"github.com/cosmos/cosmos-sdk/std"
+	"github.com/cosmos/cosmos-sdk/types/tx/signing"
+	authsigning "github.com/cosmos/cosmos-sdk/x/auth/signing"
+	authtypes "github.com/cosmos/cosmos-sdk/x/auth/types"
+
+	"github.com/pushchain/push-chain-node/app/ante"
+	appparams "github.com/pushchain/push-chain-node/app/params"
+	uexecutortypes "github.com/pushchain/push-chain-node/x/uexecutor/types"
+)
+
+// uexecutorModuleEVMAddr is the EVM address of the uexecutor module account -
+// sha256("uexecutor")[:20]. The UEA contract trusts calls coming from it
+// unconditionally, which is what makes aliasing onto it so damaging.
+const uexecutorModuleEVMAddr = "0x14191Ea54B4c176fCf86f51b0FAc7CB1E71Df7d7"
+
+const anteTestChainID = "push_9000-1"
+
+// newSignerBindingEncodingConfig returns an encoding config able to build and
+// sign real uexecutor transactions.
+func newSignerBindingEncodingConfig(t *testing.T) appparams.EncodingConfig {
+	t.Helper()
+	encCfg := appparams.MakeEncodingConfig()
+	std.RegisterInterfaces(encCfg.InterfaceRegistry)
+	authtypes.RegisterInterfaces(encCfg.InterfaceRegistry)
+	uexecutortypes.RegisterInterfaces(encCfg.InterfaceRegistry)
+	return encCfg
+}
+
+// aliasedSigner returns a `length`-byte address whose RIGHTMOST 20 bytes are the
+// uexecutor module account. common.BytesToAddress keeps exactly those bytes, so
+// every such address collapses onto the module's EVM address.
+func aliasedSigner(t *testing.T, length int) sdk.AccAddress {
+	t.Helper()
+	require.Greater(t, length, common.AddressLength)
+
+	moduleAddr := authtypes.NewModuleAddress(uexecutortypes.ModuleName)
+	require.Len(t, moduleAddr, common.AddressLength)
+	require.Equal(t, uexecutorModuleEVMAddr, common.BytesToAddress(moduleAddr).Hex())
+
+	prefix := make([]byte, length-common.AddressLength)
+	prefix[0] = 0x01
+	addr := sdk.AccAddress(append(prefix, moduleAddr...))
+	require.Len(t, addr, length)
+
+	// The whole point of the finding: this longer address truncates onto the
+	// module's EVM address downstream.
+	require.Equal(t, uexecutorModuleEVMAddr, common.BytesToAddress(addr).Hex())
+	return addr
+}
+
+// gaslessMsgFor builds one of the two user-facing gasless messages with the
+// given declared signer.
+func gaslessMsgFor(t *testing.T, msgType string, signer sdk.AccAddress) sdk.Msg {
+	t.Helper()
+	ua := &uexecutortypes.UniversalAccountId{
+		ChainNamespace: "eip155",
+		ChainId:        "11155111",
+		Owner:          "0x000000000000000000000000000000000000dead",
+	}
+
+	switch msgType {
+	case "MsgExecutePayload":
+		return &uexecutortypes.MsgExecutePayload{
+			Signer:             signer.String(),
+			UniversalAccountId: ua,
+			UniversalPayload: &uexecutortypes.UniversalPayload{
+				To:   "0x000000000000000000000000000000000000dead",
+				Data: "0xabcdef",
+			},
+			VerificationData: "0xabcdef",
+		}
+	case "MsgMigrateUEA":
+		return &uexecutortypes.MsgMigrateUEA{
+			Signer:             signer.String(),
+			UniversalAccountId: ua,
+			MigrationPayload: &uexecutortypes.MigrationPayload{
+				Migration: "0x000000000000000000000000000000000000beef",
+				Nonce:     "0",
+				Deadline:  "1",
+			},
+			Signature: "0xabcdef",
+		}
+	default:
+		t.Fatalf("unknown msg type %q", msgType)
+		return nil
+	}
+}
+
+// buildSignedTx returns a tx carrying msg whose declared signer is
+// `declaredSigner` but which is signed by `priv` - the two need not be related,
+// which is exactly the confusion the fix has to reject.
+func buildSignedTx(t *testing.T, encCfg appparams.EncodingConfig, msg sdk.Msg, declaredSigner sdk.AccAddress, priv cryptotypes.PrivKey) sdk.Tx {
+	t.Helper()
+
+	txb := encCfg.TxConfig.NewTxBuilder()
+	require.NoError(t, txb.SetMsgs(msg))
+	txb.SetGasLimit(300_000)
+
+	require.NoError(t, txb.SetSignatures(signing.SignatureV2{
+		PubKey:   priv.PubKey(),
+		Data:     &signing.SingleSignatureData{SignMode: signing.SignMode_SIGN_MODE_DIRECT},
+		Sequence: 0,
+	}))
+
+	// The gasless new-account path signs over account number 0 / sequence 0,
+	// since the account does not exist on chain yet.
+	signerData := authsigning.SignerData{
+		Address:       declaredSigner.String(),
+		ChainID:       anteTestChainID,
+		AccountNumber: 0,
+		Sequence:      0,
+		PubKey:        priv.PubKey(),
+	}
+
+	sigV2, err := clienttx.SignWithPrivKey(
+		context.Background(), signing.SignMode_SIGN_MODE_DIRECT, signerData,
+		txb, priv, encCfg.TxConfig, 0,
+	)
+	require.NoError(t, err)
+	require.NoError(t, txb.SetSignatures(sigV2))
+
+	return txb.GetTx()
+}
+
+func newSignerBindingDecorator(t *testing.T, encCfg appparams.EncodingConfig) (ante.AccountInitDecorator, *mockAccountKeeperAnte) {
+	t.Helper()
+	ak := newMockAccountKeeperAnte(sdk.AccAddress([]byte("feeCollector")))
+	return ante.NewAccountInitDecorator(ak, encCfg.TxConfig.SignModeHandler()), ak
+}
+
+// TestAccountInitDecorator_RejectsAliasedModuleSigner is the regression test for
+// F-2026-18200: a gasless tx may not declare an over-long signer that truncates
+// onto the uexecutor module address while being signed by an unrelated key.
+//
+// Hacken's PoC only used the 21-byte case; truncation works for ANY length > 20,
+// so 21, 22 and 32 bytes are all covered, against both gasless messages.
+func TestAccountInitDecorator_RejectsAliasedModuleSigner(t *testing.T) {
+	encCfg := newSignerBindingEncodingConfig(t)
+
+	for _, msgType := range []string{"MsgExecutePayload", "MsgMigrateUEA"} {
+		for _, length := range []int{21, 22, 32} {
+			t.Run(fmt.Sprintf("%s/%dbytes", msgType, length), func(t *testing.T) {
+				attackerKey := secp256k1.GenPrivKey()
+				declaredSigner := aliasedSigner(t, length)
+				msg := gaslessMsgFor(t, msgType, declaredSigner)
+				tx := buildSignedTx(t, encCfg, msg, declaredSigner, attackerKey)
+
+				aid, ak := newSignerBindingDecorator(t, encCfg)
+				ctx := newAnteTestCtx(t, false).WithChainID(anteTestChainID)
+
+				nextCalled := false
+				_, err := aid.AnteHandle(ctx, tx, false, func(ctx sdk.Context, tx sdk.Tx, simulate bool) (sdk.Context, error) {
+					nextCalled = true
+					return ctx, nil
+				})
+
+				require.Error(t, err, "aliased signer must not pass the ante chain")
+				require.True(t, sdkerrors.ErrInvalidPubKey.Is(err), "expected ErrInvalidPubKey, got: %v", err)
+				require.False(t, nextCalled, "the message must never reach execution")
+				require.False(t, ak.HasAccount(context.Background(), declaredSigner),
+					"no account may be persisted for a rejected signer")
+			})
+		}
+	}
+}
+
+// TestAccountInitDecorator_RejectsMismatchedSigner covers the general case: a
+// well-formed 20-byte signer that is simply not the address of the signing key.
+func TestAccountInitDecorator_RejectsMismatchedSigner(t *testing.T) {
+	encCfg := newSignerBindingEncodingConfig(t)
+
+	attackerKey := secp256k1.GenPrivKey()
+	victimKey := secp256k1.GenPrivKey()
+	declaredSigner := sdk.AccAddress(victimKey.PubKey().Address())
+
+	msg := gaslessMsgFor(t, "MsgExecutePayload", declaredSigner)
+	tx := buildSignedTx(t, encCfg, msg, declaredSigner, attackerKey)
+
+	aid, ak := newSignerBindingDecorator(t, encCfg)
+	ctx := newAnteTestCtx(t, false).WithChainID(anteTestChainID)
+
+	_, err := aid.AnteHandle(ctx, tx, false, emptyNext)
+	require.Error(t, err)
+	require.True(t, sdkerrors.ErrInvalidPubKey.Is(err), "expected ErrInvalidPubKey, got: %v", err)
+	require.False(t, ak.HasAccount(context.Background(), declaredSigner))
+}
+
+// TestAccountInitDecorator_AcceptsMatchingSigner is the positive control: a
+// normal 20-byte signer whose key matches still creates the account and passes.
+func TestAccountInitDecorator_AcceptsMatchingSigner(t *testing.T) {
+	encCfg := newSignerBindingEncodingConfig(t)
+
+	for _, msgType := range []string{"MsgExecutePayload", "MsgMigrateUEA"} {
+		t.Run(msgType, func(t *testing.T) {
+			key := secp256k1.GenPrivKey()
+			signer := sdk.AccAddress(key.PubKey().Address())
+			require.Len(t, signer, common.AddressLength)
+
+			msg := gaslessMsgFor(t, msgType, signer)
+			tx := buildSignedTx(t, encCfg, msg, signer, key)
+
+			aid, ak := newSignerBindingDecorator(t, encCfg)
+			ctx := newAnteTestCtx(t, false).WithChainID(anteTestChainID)
+
+			_, err := aid.AnteHandle(ctx, tx, false, emptyNext)
+			require.NoError(t, err)
+
+			acc := ak.GetAccount(context.Background(), signer)
+			require.NotNil(t, acc, "the account must be created for a legitimate gasless tx")
+			require.Equal(t, uint64(1), acc.GetSequence())
+		})
+	}
+}
+
+// TestAccountInitDecorator_SimulationUnaffected checks that the new binding
+// check keeps the SDK's `!simulate` guard, so simulation and gas estimation -
+// which carry no usable signature - keep working.
+func TestAccountInitDecorator_SimulationUnaffected(t *testing.T) {
+	encCfg := newSignerBindingEncodingConfig(t)
+
+	attackerKey := secp256k1.GenPrivKey()
+	victimKey := secp256k1.GenPrivKey()
+
+	for name, declaredSigner := range map[string]sdk.AccAddress{
+		"matching_signer":   sdk.AccAddress(attackerKey.PubKey().Address()),
+		"mismatched_signer": sdk.AccAddress(victimKey.PubKey().Address()),
+	} {
+		t.Run(name, func(t *testing.T) {
+			msg := gaslessMsgFor(t, "MsgExecutePayload", declaredSigner)
+			tx := buildSignedTx(t, encCfg, msg, declaredSigner, attackerKey)
+
+			aid, _ := newSignerBindingDecorator(t, encCfg)
+			ctx := newAnteTestCtx(t, false).WithChainID(anteTestChainID)
+
+			_, err := aid.AnteHandle(ctx, tx, true /* simulate */, emptyNext)
+			require.NoError(t, err, "simulation must not be affected by the binding check")
+		})
+	}
+}
+
+// TestAccountInitDecorator_EnforcesSignatureLimit covers F-2026-18186: the
+// new-account path short-circuits the ante chain, so it has to enforce the
+// signature count limit itself instead of verifying an unbounded multisig for
+// free.
+func TestAccountInitDecorator_EnforcesSignatureLimit(t *testing.T) {
+	encCfg := newSignerBindingEncodingConfig(t)
+
+	params := authtypes.DefaultParams()
+	numKeys := int(params.TxSigLimit) + 1
+
+	pubKeys := make([]cryptotypes.PubKey, numKeys)
+	sigs := make([]signing.SignatureData, numKeys)
+	bitArray := cryptotypes.NewCompactBitArray(numKeys)
+	for i := 0; i < numKeys; i++ {
+		pubKeys[i] = secp256k1.GenPrivKey().PubKey()
+		sigs[i] = &signing.SingleSignatureData{
+			SignMode:  signing.SignMode_SIGN_MODE_DIRECT,
+			Signature: []byte("not-checked-the-limit-trips-first"),
+		}
+		bitArray.SetIndex(i, true)
+	}
+
+	multisigPk := kmultisig.NewLegacyAminoPubKey(numKeys, pubKeys)
+	signer := sdk.AccAddress(multisigPk.Address())
+
+	txb := encCfg.TxConfig.NewTxBuilder()
+	require.NoError(t, txb.SetMsgs(gaslessMsgFor(t, "MsgExecutePayload", signer)))
+	txb.SetGasLimit(300_000)
+	require.NoError(t, txb.SetSignatures(signing.SignatureV2{
+		PubKey:   multisigPk,
+		Data:     &signing.MultiSignatureData{BitArray: bitArray, Signatures: sigs},
+		Sequence: 0,
+	}))
+
+	aid, ak := newSignerBindingDecorator(t, encCfg)
+	ctx := newAnteTestCtx(t, false).WithChainID(anteTestChainID)
+
+	_, err := aid.AnteHandle(ctx, txb.GetTx(), false, emptyNext)
+	require.Error(t, err)
+	require.True(t, sdkerrors.ErrTooManySignatures.Is(err), "expected ErrTooManySignatures, got: %v", err)
+	require.False(t, ak.HasAccount(context.Background(), signer))
+}

app/ante/ante_cosmos.go

@@ -43,7 +43,8 @@ func NewCosmosAnteHandler(ctx sdk.Context, options HandlerOptions) sdk.AnteHandl
 		// NewAccountInitDecorator must be called before all signature verification decorators and SetPubKeyDecorator
 		// - this
 		// 1. generates the account for the new accounts only for gasless transactions,
-		// 2. verifies the sig, and
+		// 2. binds the declared signer to the signing key, enforces the signature
+		//    count limit and verifies the sig, and
 		// 3. bypasses the rest of the ante chain
 		NewAccountInitDecorator(options.AccountKeeper, options.SignModeHandler),
 		// SetPubKeyDecorator must be called before all signature verification decorators

test/integration/uexecutor/chain_enabled_test.go

@@ -220,7 +220,7 @@ func TestExecutePayload_ChainEnabled(t *testing.T) {
 		ms := uexecutorkeeper.NewMsgServerImpl(testApp.UexecutorKeeper)
 
 		_, err := ms.ExecutePayload(ctx, &uexecutortypes.MsgExecutePayload{
-			Signer: "cosmos1xpurwdecvsenyvpkxvmnge3cv93nyd34xuersef38pjnxen9xfsk2dnz8yek2drrv56qmn2ak9",
+			Signer: testSigner,
 			UniversalAccountId: &uexecutortypes.UniversalAccountId{
 				ChainNamespace: "eip155",
 				ChainId:        "11155111",