How much was lost in the SquidMulticall Approval Exploitation hack?

The SquidMulticall Approval Exploitation hack resulted in $517K in losses on April 07, 2026.

What attack technique was used in the SquidMulticall Approval Exploitation exploit?

The SquidMulticall Approval Exploitation 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.

SquidMulticall Approval Exploitation Hack

TOTAL LOST $517K

Low Apr 07, 2026 Access Control

Affected Chain 2026 Incident surface

Recovered - No recovery reported

All-Time Rank #968 By amount stolen

Protocol Type Exploit/Access control Target category

Incident Overview

Quick Summary

On April 7, 2026, a victim lost $517K across five chains (Arbitrum, BSC, Avalanche, Optimism, Base) when an attacker exploited pre-existing MAX_UINT token approvals to a SquidMulticall contract, using the permissionless run() function to execute transferFrom calls and drain tokens directly from the victim's wallet.

Details of the Exploit

The victim had previously granted unlimited (MAX_UINT) approvals to a SquidMulticall-related contract deployed at the same address across all five chains. The attacker didn't need to phish or trick the victim again. They simply used the permissionless run() entrypoint in the contract to execute crafted multicalls containing transferFrom payloads.

This drained tokens directly from the victim's address across all chains where approvals existed.

Block Data Reference

Victim: 0xaCc0c1f6…f40E98

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

Incident Report

Protocol / Project SquidMulticall Approval Exploitation

Date of Incident April 07, 2026

Attack Technique Access Control

Classification Exchange (DEX)

Primary Source View Post-Mortem

Protocol Information

Protocol Type Exploit/Access control

Official Website www.squidrouter.com/

Protocol Twitter/X @squidrouter

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 SquidMulticall Approval Exploitation'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 SquidMulticall Approval Exploitation, these are the critical security checks that could have prevented this incident (April 2026).

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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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://x.com/Phalcon_xyz/status/2041463211493662942

Threat Assessment

Severity Level

LOW

Attack Vector Access Control
Root Cause Exchange (DEX)
Year 2026

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