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Introduction:
The crowdsourced security testing model relies on accurate vulnerability triage to incentivize researchers and protect organizations. However, when a researcher submits a valid front-running vulnerability with multiple on-chain proofs of concept (POCs), only to have it rejected as “lacking security impact,” later upgraded to P1, and finally closed as a duplicate, it exposes deep flaws in the bug bounty ecosystem. This article dissects the technical anatomy of blockchain front-running attacks, explores Bugcrowd’s triage policies, and provides a step‑by‑step guide to discovering, proving, and mitigating such vulnerabilities – while examining what happens when the platform fails the researcher.
Learning Objectives:
- Understand the mechanics of blockchain front‑running attacks and how they differ from traditional web vulnerabilities.
- Learn how to craft a high‑impact vulnerability report with reproducible on‑chain proofs of concept.
- Master practical mitigation strategies, including transaction ordering techniques and smart contract design patterns.
You Should Know:
- Extending the Researcher’s Experience: From N/A to Duplicate
Taylor Hawkins submitted a front‑running vulnerability in March, providing clear evidence of the attack vector. The report was closed as “Not Applicable” because it supposedly lacked security impact. After resubmitting in May with three on‑chain proofs of concept (POCs), the severity was upgraded from P2 to P1 – yet the report was eventually closed as a duplicate, citing a prior submission that used identical methods.
This pattern is not unique. Other researchers have reported valid XSS bugs rejected by Bugcrowd but accepted on HackerOne, or had reports closed as N/A only to be reopened after escalation. In one instance, a triager closed six reports as N/A; after a re‑review request, all were triaged and resolved.
What this reveals:
- Inconsistent triage criteria – The same vulnerability can be considered “no impact” or “critical” depending on the triager.
- Delayed recognition – Even with strong evidence, reports can languish for months.
- Duplicate abuse – Closing a report as a duplicate of an earlier submission, even when the earlier submission was initially rejected, undermines trust.
Practical takeaway for researchers:
Always document your submission timeline and request formal re‑evaluations when a report is unjustly closed. Use Bugcrowd’s “Request a Response” escalation process if no update occurs within seven business days.
2. Front‑Running Attacks: A Technical Deep Dive
Front‑running is a class of MEV (Maximal Extractable Value) attack where an adversary observes a pending transaction and inserts their own transaction with a higher gas price to be executed first. This is particularly dangerous in decentralized finance (DeFi) contexts because it can lead to direct financial loss.
How it works (Ethereum example):
- A user submits a transaction `tx1` (e.g., swapping tokens on Uniswap).
- An attacker monitors the mempool and sees
tx1. - The attacker submits `tx2` with a higher gas price, performing the same swap just before `tx1` executes.
4. `tx2` executes, altering the pool state, and `tx1` then executes at a less favorable rate – the attacker profits from the price slippage.
Proof of Concept (Solidity test using Hardhat):
// test/FrontRunning.t.sol
pragma solidity ^0.8.0;
import "forge-std/Test.sol";
import "../src/VulnerableSwap.sol";
contract FrontRunningTest is Test {
VulnerableSwap public swap;
address public user = address(0x1);
address public attacker = address(0x2);
function setUp() public {
swap = new VulnerableSwap();
vm.deal(user, 10 ether);
vm.deal(attacker, 1 ether);
}
function testFrontRun() public {
// User submits a swap transaction
vm.prank(user);
uint256 expectedOutput = swap.swap{value: 1 ether}();
// Attacker front-runs with higher gas
vm.prank(attacker);
vm.txGasPrice(200 gwei); // higher than user's 100 gwei
swap.swap{value: 1 ether}();
// User's transaction now executes with less favorable rate
vm.prank(user);
uint256 actualOutput = swap.swap{value: 1 ether}();
assertLt(actualOutput, expectedOutput);
}
}
Detection with Go‑Ethereum (geth):
Monitor the mempool for transactions targeting the same contract function:
Install geth
sudo add-apt-repository -y ppa:ethereum/ethereum
sudo apt-get update
sudo apt-get install geth
Start a light client and subscribe to pending transactions
geth --light --ws --ws.api "eth,txpool" --ws.origins "" attach
Inside the console:
<blockquote>
txpool.content.pending
eth.subscribe('pendingTransactions', function(err, result){ console.log(result); })
Mitigation strategies:
- Commit‑reveal schemes – Users submit a hash of their transaction, then reveal the actual data in a later block.
- Submarine sends – Transactions are sent to a private mempool (e.g., Flashbots) to avoid public visibility.
- Deterministic ordering – EIP‑7956 proposes block‑level randomness to defeat front‑running.
- MEV‑less protocols – EIP‑8099 removes validators’ ability to reorder transactions.
3. How to Write an Ironclad Vulnerability Report
A report that survives triage must be clear, reproducible, and include a strong impact statement. Based on Bugcrowd’s guidelines and researcher experiences, follow this template:
Report structure:
- – “Front‑running vulnerability allows theft of user funds in swap function”
- Description – Explain the attack vector, why it matters, and which users are affected.
- Steps to Reproduce – Provide precise commands or code. For a front‑running POC:
Clone the target repository git clone https://github.com/victim/protocol.git cd protocol Install dependencies npm install npx hardhat compile Run the exploit test npx hardhat test test/frontrun.js --network hardhat
- Proof of Concept – Attach a video (e.g., using Loom or OBS) showing the exploit in a local testnet or forked mainnet.
- Impact – Quantify the potential loss. “An attacker could steal up to 100 ETH per day by front‑running the `swap()` function.”
- Suggested Fix – Recommend a commit‑reveal pattern or integration with a private mempool.
Common mistakes that lead to N/A or duplicate status:
– Submitting without a clear security impact.
– Providing a POC that only works in an unrealistic environment.
– Failing to search for existing reports before submitting.
Pro tip: If your report is closed as N/A, request a re‑evaluation and reference Bugcrowd’s own Vulnerability Rating Taxonomy (VRT) version 1.15, which explicitly includes blockchain front‑running as a valid vulnerability class.
4. Windows and Linux Commands for Transaction Analysis
Linux (using `jq` and `curl` with Infura):
Get the latest block number
curl -X POST https://mainnet.infura.io/v3/YOUR_PROJECT_ID \
-H "Content-Type: application/json" \
-d '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}' | jq '.result'
Fetch transactions from a specific block
curl -X POST https://mainnet.infura.io/v3/YOUR_PROJECT_ID \
-H "Content-Type: application/json" \
-d '{"jsonrpc":"2.0","method":"eth_getBlockByNumber","params":["0x10d4f5", true],"id":1}' \
| jq '.result.transactions[] | {hash: .hash, from: .from, to: .to, value: .value}'
Windows (PowerShell with `Invoke-RestMethod`):
$body = @{
jsonrpc = "2.0"
method = "eth_getTransactionByHash"
params = @("0x7e4c5a9f...")
id = 1
} | ConvertTo-Json
Invoke-RestMethod -Uri "https://mainnet.infura.io/v3/YOUR_PROJECT_ID" `
-Method Post `
-Body $body `
-ContentType "application/json"
Monitoring the mempool (using `txpool` namespace in geth):
Linux geth attach http://localhost:8545 --exec "txpool.content" Windows (PowerShell) geth attach http://localhost:8545 --exec "txpool.content" | Out-File -FilePath mempool.json
5. Bugcrowd Triage Process: How Duplicates Are Determined
Bugcrowd’s official guidance states that a duplicate occurs when a submission “reports the same root cause and the same fix as a previously submitted report”. However, the platform’s “Three Principles of Bug Bounty Duplicates” acknowledges that “multiple vulnerabilities of the same vulnerability class does not equal them all being the same vulnerability”. This nuance is often lost in practice.
What the triager sees:
- A dashboard with pending submissions.
- Suggested duplicates based on VRT classification.
- Ability to mark as duplicate and link to the original report.
Why duplicates happen unfairly:
- The original report may have been closed as N/A or out of scope, but the triager still considers it “prior art.”
- A researcher who submitted a weaker version of the same bug may receive credit, while the later, more thorough submission is marked duplicate.
- Bugcrowd’s AI filtering models sometimes mark valid reports as duplicates or false positives.
How to dispute a duplicate closure:
- Politely comment on the submission, explaining why the root cause differs from the cited duplicate.
- Request an escalation via Bugcrowd’s “Report an Incident” form for duplicate abuse.
- If unresolved, take the discussion to public forums (HackerOne’s community, Reddit, or LinkedIn) to apply social pressure.
6. Cloud Hardening for Blockchain Nodes
Running a blockchain node in the cloud introduces additional attack surfaces. Use these hardening steps for an Ethereum full node on AWS:
AWS CLI commands to secure an EC2 instance:
Create a security group that only allows SSH from your IP and P2P port from anywhere
aws ec2 create-security-group --group-name eth-node-sg --description "Security group for Ethereum node"
aws ec2 authorize-security-group-ingress --group-id sg-xxxxx --protocol tcp --port 22 --cidr YOUR_IP/32
aws ec2 authorize-security-group-ingress --group-id sg-xxxxx --protocol tcp --port 30303 --cidr 0.0.0.0/0
Launch an instance with encrypted EBS volume
aws ec2 run-instances --image-id ami-0c55b159cbfafe1f0 --instance-type t3.medium \
--block-device-mappings "DeviceName=/dev/sda1,Ebs={VolumeSize=200,VolumeType=gp3,Encrypted=true}" \
--security-group-ids sg-xxxxx
Linux hardening inside the instance:
Disable root SSH login sudo sed -i 's/PermitRootLogin yes/PermitRootLogin no/' /etc/ssh/sshd_config Set up a firewall (ufw) sudo ufw default deny incoming sudo ufw default allow outgoing sudo ufw allow 22/tcp sudo ufw allow 30303/tcp sudo ufw enable Run geth as a non‑root user sudo useradd -m -s /bin/bash ethereum sudo -u ethereum geth --datadir /home/ethereum/.ethereum --syncmode "fast" --http --http.addr 0.0.0.0
7. API Security for Bug Bounty Platforms
Bug bounty platforms themselves are API‑heavy and can be vulnerable. When testing a platform like Bugcrowd, consider these API security checks:
Testing for mass assignment (using curl):
Attempt to change your bounty payout address via an API call
curl -X PATCH https://api.bugcrowd.com/v1/researchers/me \
-H "Authorization: Bearer YOUR_TOKEN" \
-H "Content-Type: application/json" \
-d '{"payout_address": "0xAttackerAddress", "role": "admin"}'
Testing for IDOR (Insecure Direct Object Reference):
Try to access another researcher's submission curl https://api.bugcrowd.com/v1/submissions/12345 \ -H "Authorization: Bearer YOUR_TOKEN" If you can see someone else's submission, that's IDOR
Testing for rate limiting:
Send 100 rapid requests to the submission endpoint
for i in {1..100}; do
curl -X POST https://api.bugcrowd.com/v1/submissions \
-H "Authorization: Bearer YOUR_TOKEN" \
-H "Content-Type: application/json" \
-d '{"title":"test","description":"test"}' &
done
If all succeed, the API is vulnerable to brute‑force attacks.
What Undercode Say:
- Key Takeaway 1: A vulnerability’s validity should not depend on a single triager’s interpretation; platforms must implement standardized, transparent re‑evaluation mechanisms. The fact that a report can be rejected as N/A, upgraded to P1, and then closed as a duplicate underscores systemic inconsistency.
- Key Takeaway 2: For blockchain vulnerabilities, on‑chain proofs of concept are the gold standard – yet they were still insufficient in this case. Researchers should also archive their POCs on immutable platforms like IPFS or Arweave to prevent later disputes about originality.
Analysis: The Bugcrowd incident highlights a growing rift between crowdsourced security platforms and the researcher community. While platforms tout AI‑assisted triage and high acceptance rates, anecdotal evidence suggests that reports often fall victim to triager bias, misclassification, or deliberate duplicate closures to avoid payouts. For front‑running vulnerabilities – which are uniquely suited to on‑chain demonstration – the technical bar for acceptance should be lower, not higher. The use of three separate POCs should have eliminated any ambiguity about reproducibility. Instead, the researcher was forced into a Kafkaesque cycle of resubmission, status upgrades, and final dismissal. This erodes trust in the very model that bug bounties were designed to foster.
Expected Output:
Introduction: [as above]
What Undercode Say:
- Key Takeaway 1 …
- Key Takeaway 2 …
Prediction: As blockchain adoption grows, front‑running and other MEV attacks will become a primary focus of bug bounty programs. However, unless platforms overhaul their triage processes to include mandatory expert review for blockchain vulnerabilities, researchers will migrate to specialized platforms like Immunefi. Bugcrowd’s VRT 1.15 update is a step in the right direction, but without transparent duplicate handling and a binding appeals process, the platform risks losing its most skilled blockchain researchers to competitors. Within two years, we can expect a separate, blockchain‑focused bug bounty standard to emerge – one that defines clear rules for POC acceptance and duplicate resolution.
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IT/Security Reporter URL:
Reported By: Taylor Hawkins – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
