#37577 [BC-Insight] `tx.origin` Usage in Group Management Contract Allows Phishing Attack for Unauthorized Actions

Submitted on Dec 9th 2024 at 16:37:44 UTC by @cheems for Attackathon | Ethereum Protocol

• Report ID: #37577

• Report Type: Blockchain/DLT

• Report severity: Insight

• Target: https://github.com/hyperledger/besu

• Impacts:

  • Direct loss of funds

Description

Brief/Intro

A critical vulnerability exists in the on-chain group management contract, introduced in PR #1288, where tx.origin was used to verify the contract owner. This allows a malicious contract to impersonate the owner and bypass ownership checks, enabling unauthorized users to lock/unlock the contract or modify group membership. The issue arises from the addition of tx.origin as a check for ownership, which was initially introduced as part of removing the enclave key and ensuring only the creator could update the contract.

Vulnerability Details

In this PR (https://github.com/hyperledger/besu/pull/1288), the intention was to ensure that only the creator's account could add/remove members and update the management contract. However, using tx.origin to validate ownership exposes the contract to phishing attacks, where a malicious contract can call the vulnerable contract on behalf of the attacker. Since tx.origin refers to the original transaction sender, the attacker only needs to initiate the call (not execute the exploit directly), allowing them to bypass the ownership checks.

Impact Details

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References

Add any relevant links to documentation or code

Link to Proof of Concept

https://gist.github.com/SamruddhiNavale/100b48157a7101d53bee9056b2a7dbb7

Proof of Concept

Proof of Concept

pragma solidity ^0.8.0;

interface IVulnerableContract {
    function lock() external;
    function unlock() external;
}

contract MaliciousContract {
    IVulnerableContract public vulnerableContract;

    constructor(address _vulnerableContract) {
        vulnerableContract = IVulnerableContract(_vulnerableContract);
    }

    function attackLock() public {
        vulnerableContract.lock(); // Attack via tx.origin impersonation
    }

    function attackUnlock() public {
        vulnerableContract.unlock(); // Attack via tx.origin impersonation
    }
}

Steps to Reproduce:

1. Deploy the Vulnerable Contract on a local test network.

2. Deploy the Malicious Contract, passing the vulnerable contract address.

3. Call attackLock() or attackUnlock() from the malicious contract.

4. Verify the contract state is locked/unlocked by the attacker.

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Expected Result:

The contract should only allow the actual owner to lock/unlock or modify its state.

Actual Result:

The malicious contract can lock/unlock or modify the contract state due to the tx.origin vulnerability.

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Impact:

This vulnerability allows attackers to impersonate the contract owner and perform unauthorized actions, bypassing the intended ownership checks. It can lead to unauthorized updates to the contract and loss of control over group management.

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Mitigation Recommendations:

1. Avoid Using tx.origin for ownership checks.

2. Use msg.sender for proper access control.

3. Implement proper access control mechanisms like onlyOwner.

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Conclusion:

This vulnerability, introduced in PR #1288, exposes the contract to phishing attacks by using tx.origin. The malicious contract only needs to initiate the call, not execute the exploit directly, to bypass ownership checks.