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[Source](https://pixabay.com/photos/woman-businesswoman-business-3441011/)
Introduction
In the realm of smart contracts on blockchain networks, especially Ethereum, one can find a delegate call attack which is a security vulnerability. When a contract uses the delegatecall in order to implement code in its own context as it does in the other contract that is expensive, that’s when this type of attack occurs. Though the primary aim of any delegatecall is to improve modularity and encourage code reusability, abused entities may be available for attackers to exploit.
The major reason as to why a delegated call attack is catastrophic is because it can alter the included contract’s state. When an attacker is able to attack the contract being invoked or the parameter being passed-in, then the attacker is able to target the state of the initial called contract which can radiate wealth losses or other catastrophes. Because of the high consequences mostly these attacks bring, not only bear developers but also users of these systems how such attacks happen is very important.
In the blockchain space, delegate call based attacks are rather notorious as they can completely bypass normal security restrictions and readily access the state of a smart contract. Hence it becomes necessary to ensure that code security is embedded in normal procedures and eliminate too much dependence on other people’s contracts when creating new ones.
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Manipulating External Contracts: One technique in delegate call attacks involves external contracts. If a smart contract uses delegate call to communicate with an external contract, it sends its own context to the called contract. If the address of the external contract is known and has become compromised, an attacker can use that external contract to change the state variables of the first contract, including ownership or fund-transfer mechanisms.
Usually, just knowing the external contract's address isn't sufficient for this kind of attack. The attacker must have already injected code into this particular (and externally-facing) version of an object likely to be reused by multiple contracts. Given that delegate call assumes the calling context, you gain access to relevant arbitrary state information that may allow unauthorized operations like changing ownership or transferring funds.
To prevent this, developers should make sure that the external contracts they call via delegatecall are trusted and have been properly audited. Avoiding calls to third-party contract or limiting them to trusted ones can help with mitigating this risk.
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Malicious Code Injection Another method is to insert malicious code into the delegate call itself. The delegate call function executes the code of the called contract, but uses the storage and execution context of the original contract. If malicious code is inserted into a delegate call function it can modify the state of the original contract without permission.
[Source](https://pixabay.com/photos/internet-cyber-network-finger-3629639/)
For instance, if a vulnerable contract delegates calls to another malicious contract, an attacker can manipulate function logic or variables in storage. This may allow an attacker to access sensitive data such as account balances, control over funds or even destroy your contract if there’s a suicide function exposed. A famous example was the Parity Wallet incident.
The best way to mitigate this kind of attack is to make sure that only trusted and well audited contracts are ever invoked via delegatecall. Also, by validating input parameters in a careful way and by minimizing the use of delegate calls it is possible to avoid also these kind of injected attacks.
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Passing Malicious Parameters: The delegate call technique too involves passing relevant parameters with malicious intent which is simply another risk exploitation technique. In this case, the called contract uses the delegatecall of the calling contract itself to perform some actions on the external contracts by passing the arguments. If the external contract makes any assumptions on the input parameters and does not validate them thoroughly, then it could perform actions that are not meant to be executed.
For example, a malicious user can design a valid action that causes the delegate call to be performed in an unexpected way by providing such inputs which are not intended. This is dangerous because in decentralized finance (DeFi) applications where there are series of complex financial transactions that require correct inputs and state.
In this case, it is critical that developers implement input limitations not only in the original contract but also in the called contract. It is very important where such functions which receive parameters in delegatecall format should be protected from improper inputs so as to protect the security of the contract.
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Reentrancy Vulnerability Exploitation: A delegate call attack can exploit reentrancy vulnerabilities to drain funds or modify contract states. Reentrancy happens when a contract temporarily hands over control to another contract (through delegatecall), allowing the called contract to re-enter the original contract before the first transaction is finished. This enables attackers to execute the same function multiple times before the state is updated.
In a delegate call attack, the attacker takes advantage of the delegatecall to repeatedly invoke functions that interact with the original contract’s state, enabling them to perform transactions over and over. This leads to multiple unintended changes, such as transferring funds or modifying state variables.
To mitigate reentrancy, developers can use secure coding practices, like the “checks-effects-interactions” pattern, which ensures that state changes are made before any external calls. Additionally, implementing safeguards such as reentrancy guards can help prevent multiple executions of critical functions.
Conclusion
[Source](https://pixabay.com/photos/cyber-security-cybersecurity-3480163/)
Delegate call attacks represent a serious risk to smart contracts because of how the delegatecall function operates, enabling external contracts to run within the context of the calling contract. By grasping methods such as manipulating external contracts, injecting harmful code, passing malicious parameters, and taking advantage of reentrancy vulnerabilities, developers can enhance the security of their contracts. Adopting robust coding practices, performing thorough audits, and minimizing dependence on delegate calls are essential strategies for reducing these risks.
