How much was lost in the Silo Finance hack?

The Silo Finance hack resulted in $546K in losses on June 25, 2025.

What attack technique was used in the Silo Finance exploit?

The Silo Finance exploit utilized fillQuote silo.borrow() Exploit. 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.

Silo Finance Hack

TOTAL LOST $546K

Low Jun 25, 2025 fillQuote silo.borrow() Exploit ethereum

Affected Chain ethereum Incident surface

Recovered - No recovery reported

All-Time Rank #979 By amount stolen

Auditors 1 Prior security audit

Incident Overview

SiO2 Finance is the Astar-native lending hub supporting both EVM and WASM.

Incident Report

Protocol / Project Silo Finance

Date of Incident June 25, 2025

Affected Chain(s) ethereum

Attack Technique fillQuote silo.borrow() Exploit

Classification Protocol Logic

Primary Source View Post-Mortem

Protocol Information

Protocol Type Lending

Smart Contract Language Solidity

Official Website www.sio2.finance

Protocol Twitter/X @SiO2_Finance

Market Context at Time of Hack

Token Price at Hack $0.0450

Market Cap at Hack $16.9M

% of Market Cap Stolen 3.22%

Token Categories

Ethereum Ecosystem Arbitrum Ecosystem Sonic Ecosystem

Protocol Links

GitHub Discord Reddit

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 Deep understanding of fillquote silo.borrow() exploit and Solidity and EVM internals

Capital Required Seed capital to cover gas and initial position setup

On-Chain Access Ability to interact with ethereum smart contracts and deploy a custom exploit contract

Protocol Analysis Identification of the exploitable vulnerability in Silo Finance's contract logic - root cause: protocol logic

Execution Speed Precise transaction ordering and timing to exploit the vulnerability within a single atomic block

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 fillQuote silo.borrow() Exploit audit checklist and test coverage

Audited by Audit Report 1 — still lost $546K. Prior audits don't guarantee safety, especially after post-audit code changes.

If you're auditing a protocol with similar architecture to Silo Finance, these are the critical security checks that could have prevented this incident (June 2025).

Verify all logic paths related to fillQuote silo.borrow() Exploit are guarded by proper access controls and input validation
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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Security Audit History

Audit Report 1 Report

Sources & References

01
Source 1 https://x.com/CertiKAlert/status/1937882770216452174

Threat Assessment

Severity Level

LOW

Attack Vector fillQuote silo.borrow() Exploit
Root Cause Protocol Logic
Year 2025

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