How much was lost in the Fixed Float hack?

The Fixed Float hack resulted in $26.1M in losses on February 16, 2024.

What attack technique was used in the Fixed Float exploit?

The Fixed Float 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.

Fixed Float Hack

TOTAL LOST $26.1M

High #191 All-Time Feb 16, 2024 Access Control

Affected Chain 2024 Incident surface

Recovered - No recovery reported

All-Time Rank #191 By amount stolen

Protocol Type Exploit/Access control Target category

Incident Overview

Quick Summary

FixedFloat cryptocurrency exchange was exploited, resulting in the loss of 409.304 BTC and 1,728.48 ETH worth approximately $26,130,157 USD.

Details of the Exploit

FixedFloat, a cryptocurrency exchange platform, was exploited on February 16, 2024. The attacker stole approximately $26.1 million worth of Bitcoin and Ethereum. Most of the money stolen was on the Bitcoin chain, funds were distributed between multiple addresses.

The stolen funds on the Ethereum Mainnet were transferred to the eXch exchange through multiple addresses, with a small portion deposited into HitBTC. Additional clarifications regarding the incident were not disclosed by FixedFloat.

Block Data Reference

Attacker Addresses:

https://www.blockchain.com/btc/address/bc1q2skp47p9f5mr4n4m27k66v0l68gh3xdd7ad4e5

https://etherscan.io/address/0x85c4fF99…3Fa085

Funds Holder as of Feb 19, 2024:

https://etherscan.io/address/0x2c01cAB6…F22d8F

Malicious Transactions:

https://etherscan.io/tx/0x1faa4861…b4ece8

https://etherscan.io/tx/0x8f0bd0a0…6ce740

https://etherscan.io/tx/0x98226160…88df41

https://etherscan.io/tx/0x15f7ac31…e5da6d

https://blockstream.info/tx/9822616097948dab2048395c4d887dbb1f99273e5cc40de2d86639013588df41

https://blockstream.info/tx/15f7ac31837c8dba597f46359857205df1c41573c4bb489b5a81fd058be5da6d

HitBTC Deposit Transaction:

https://etherscan.io/tx/0xe717258e…889e69

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

Incident Report

Protocol / Project Fixed Float

Date of Incident February 16, 2024

Attack Technique Access Control

Classification Exchange (DEX)

Primary Source View Post-Mortem

Protocol Information

Protocol Type Exploit/Access control

Official Website fixedfloat.com/about

Protocol Twitter/X @FixedFloat

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 Fixed Float'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 Fixed Float, these are the critical security checks that could have prevented this incident (February 2024).

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.

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Post-Incident Timeline

2024-04-02

Apr 2, 2024 $2.8M was withdrawn from FixedFloat's hot wallet on the $ETH chain. FixedFloat team has announced that "On April 1, we were again attacked by the attackers who were behind the February 16 hack. The attackers did not stop there and continued to use various methods to try to hack our service again."

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://twitter.com/FixedFloat/status/1759216185185288653
02
Web Archive https://archive.is/7ObTi

Threat Assessment

Severity Level

HIGH

Attack Vector Access Control
Root Cause Exchange (DEX)
Year 2024

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