How much was lost in the Boy X Highspeed hack?

The Boy X Highspeed hack resulted in $140M in losses on October 30, 2021.

What attack technique was used in the Boy X Highspeed exploit?

The Boy X Highspeed exploit utilized Access Control. Understanding this attack vector is critical for smart contract auditors and developers building secure DeFi protocols.

How can developers prevent similar smart contract attacks?

Preventing smart contract hacks requires a combination of secure coding practices, thorough security audits, and understanding common attack vectors like reentrancy, oracle manipulation, and access control flaws. Smart Contract Hacking (SCH) provides hands-on training to help developers and auditors identify and prevent vulnerabilities before deployment.

Boy X Highspeed Hack

TOTAL LOST $140M

Critical #64 All-Time Oct 30, 2021 Access Control

Affected Chain 2021 Incident surface

Recovered - No recovery reported

All-Time Rank #64 By amount stolen

Protocol Type Exploit/Access control Target category

Incident Overview

Quick Summary

BXH protocol was attacked by a private key compromise, and more than 130,000,000 $USD worth of assets stolen

Details of the Exploit

BXH DeFi lending protocol was attacked by private key disclosure, by gaining control over the target smart contract, the attacker withdrew all funds at the following transaction:

https://bscscan.com/tx/0x6466cad9…74ac84

Funds recipient (attacker's contract) transferred all funds directly into the attacker's EOA:

https://bscscan.com/address/0x13b81fa9…f9d18c#tokentxns

Part of the stolen funds was bridged through Ren protocol into Bitcoin:

https://bscscan.com/tx/0xa54f7d9c…53d820

https://bscscan.com/tx/0xa317f711…cd5331

https://bscscan.com/tx/0x15ea305d…7cfb46

https://bscscan.com/tx/0xbb585cb7…d82c91

https://bscscan.com/tx/0xfa4b24b0…edcbb7

Part of the stolen funds was transferred to another EOA:

https://bscscan.com/tx/0x80636964…af6099

https://bscscan.com/tx/0xce864913…00e6ff

https://bscscan.com/tx/0x5c0b2fd4…aab411

Block Data Reference

The attacker's address:

https://bscscan.com/address/0x48c94305…c27d79

Attacker's contract, used for withdrawing assets:

https://bscscan.com/address/0x13b81fa9…f9d18c

The funds' recipient bridged tokens through AnySwap into Ethereum:

https://bscscan.com/address/0x44cc771f…9b6316#tokentxns

The address leads to the Ethereum blockchain, which has a connection with the Binance wallet:

https://etherscan.io/address/0x44cc771f…9b6316

This is classified as a Access Control Attacks . Compare similar hacks →

Incident Report

Protocol / Project Boy X Highspeed

Date of Incident October 30, 2021

Attack Technique Access Control

Classification Other

Primary Source View Post-Mortem #1 View Post-Mortem #2

Protocol Information

Protocol Type Exploit/Access control

Affected Token BXH

Official Website www.bxh.com/

Protocol Twitter/X @BXH_Blockchain

Team Anonymous

Source Code Unverified

What the Attacker Needed to Succeed

Understanding the prerequisites for this type of attack helps auditors identify protocols that are most at risk and helps developers build better defenses.

Technical Knowledge Operational-security tradecraft (phishing, malware, leaked seed phrases, or insider access) to obtain treasury signing authority

Capital Required Minimal capital - only enough to cover gas while draining the compromised accounts

On-Chain Access Valid signing authority over the compromised wallets / multisig signers, allowing direct transfer of funds or stake authorization

Target Reconnaissance Identification of Boy X Highspeed's high-value treasury accounts and the authority / multisig structure controlling them

Execution Speed Speed to drain the compromised accounts before the team detects the breach and revokes signing authority or freezes the assets

Obfuscation Plan A strategy to launder and move stolen funds - typically through mixers, cross-chain bridges, or decentralized DEX swaps to resist tracing

What Auditors Should Check

Could this have been caught in audit? Likely — with a thorough Access Control audit checklist and test coverage

If you're auditing a protocol with similar architecture to Boy X Highspeed, these are the critical security checks that could have prevented this incident (October 2021).

Verify all logic paths related to Access Control are guarded by proper access controls and input validation - see the Access Control Attacks attack class for patterns
Review privileged functions (owner, admin, governance) for potential abuse vectors - centralization risks should be documented and bounded with timelocks or multi-sigs

Master these auditing techniques with hands-on labs and real exploit scenarios in the Smart Contract Hacking course.

Free Trial

Related Attack Classes

The technique used in this hack maps to these vulnerability classes in our security curriculum:

See all Access Control Attacks examples →

Access Control Attacks

Sources & References

01
Source 1 https://beincrypto.com/bxh-defi-exploit-drains-estimated-130m-to…
02
Source 2 https://www.coindesk.com/tech/2021/11/01/139m-bxh-exchange-hack-…

Threat Assessment

Severity Level

CRITICAL

Attack Vector Access Control
Root Cause Other
Year 2021

Learn to Prevent the Next Boy X Highspeed

The Boy X Highspeed hack is one of many attacks that skilled auditors are trained to detect before deployment. Master real exploit patterns and defense techniques with hands-on Web3 security training.

Start Free Trial Browse Attack Library