An Overview of Integer Overflow Attacks

Good contracts are one of essentially the most outstanding highlights within the blockchain panorama. You may discover how good contracts may leverage well-defined interfaces to work together with one another to conduct monetary transactions. Nevertheless, the trustless setting with none intermediaries can create alternatives for malicious actors. Hackers may exploit vulnerabilities akin to integer overflow assaults to realize monetary income. 

Good contract vulnerabilities have led to losses price greater than $7 billion as of now. Hackers can faucet into good contract vulnerabilities and expose delicate info or steal precious property of customers. Since good contracts are a outstanding facet of web3, it is very important concentrate on issues like integer overflow and comply with the perfect practices for resolving such points. 

Web3 is the subsequent era of the web, which might provide a brand new method to interacting with digital companies. The solutions to ‘What is integer overflow attack?’ are important for planning the roadmap to web3 adoption. Nevertheless, you’ll be able to handle the issues because of integer overflow solely by understanding the vulnerability. Allow us to discover out the basics of integer overflow and how one can keep away from the vulnerability to your good contracts.

What’s Integer Overflow?

The issues with good contract safety current the largest challenges for large-scale adoption of web3 and blockchain. Integer overflow is one of the favored points within the area of good contract safety. One of the best ways to grasp an integer overflow assault instance can be to grasp the illustration of numbers in computer systems. 

Digital transformation is the necessity of the hour, and good contracts serve an important position in automation of the method for executing transactions and agreements. Nevertheless, the vulnerabilities and dangers related to good contracts may result in issues with safety and effectiveness. Integer overflow and underflow are the widespread vulnerabilities related to good contracts. What’s the major purpose for such points?

It is very important word that computer systems retailer information within the type of numbers or textual content. The identical situation is relevant to the Ethereum Digital Machine or EVM, which gives fixed-sized information sorts for specifying integers. The integer overflow good contract vulnerability emerges from the truth that a particular integer variable may solely characterize a particular vary of numbers. 

For instance, a uint8 information sort for an integer may retailer numbers from 0 to 255. In case you retailer an integer higher than 256, then the worth of the uint8 will return 0. With none precautions, malicious actors may exploit variables in Solidity for unchecked inputs. If calculations may generate numbers outdoors the vary of a particular information sort for storing the numbers, then you would encounter integer overflow points.

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Causes for Integer Overflow

Integer overflow shouldn’t be a brand new vulnerability for good contracts. The origins of integer overflow could be traced to the element that majority of pc languages may work with integers solely having a restricted vary. The integer overflow Solidity contracts can exhibit, in sure circumstances, factors on the vary of calculations. 

When the calculations of a end result are past the vary of a particular information sort, then the end result would violate accuracy and customary assumptions. As an illustration, addition of two giant numbers may generate a small quantity. In some circumstances, you might need a multiplication of two constructive values for producing a adverse product. 

Bugs like integer overflow are widespread situations for low-level languages akin to C++ and C. As well as, components like guide reminiscence administration, weak sort security, and lack of vary checking may additionally exacerbate the impression of integer overflow. Such sorts of flaws may current the inspiration for full remote-code execution exploits. The massive downside proper now’s the growth of a vulnerability class from low-level programming in a radically totally different setting.

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Working of Integer Overflow

A very powerful spotlight of integer overflow assaults is the working mechanism of the assaults. Overflow eventualities are widespread in eventualities the place it’s a must to transmit a big batch of values to totally different receivers. Integer overflows are widespread when you’ll be able to evaluate the whole worth of person tokens to the whole quantity of funds in airdrops or whereas giving tokens to a person. Within the occasion of overflow, algorithms have to match the decrease worth of overflowed tokens to the whole token worth. The algorithm would additionally make sure that customers know that they’ve an sufficient quantity of tokens for funding the transaction.       

Allow us to assume that an account has 100 tokens, and also you ship 99 tokens as the associated fee of a purchase order and 1 token because the tip. Subsequently, the whole quantity of the transaction is 100 tokens. The quantity would return to zero in a case when the integer may retailer solely two digits. The integer overflow assault instance may result in points when the assertion couldn’t be managed with safe mathematical strategies for sanitizing the output. 

You may take an instance of a ‘TimeLock’ contract, which lets you deposit Ether. Nevertheless, you would need to await at the least one week earlier than withdrawing the quantity deposited within the contract. You should use a mapping generally known as ‘lockTime’ within the contract to outline the time after which you’ll withdraw the quantity deposited within the contract. 

Upon depositing Ether into the contract, the good contract would implement two duties. First of all, it could replace the stability, after which it could replace the ‘lockTime’ parameter to at least one week. Subsequently, the integer overflow good contract instance would limit depositors from withdrawing Ether from the contract for at the least one week. What would you do on the time of withdrawal? The ‘withdrawal’ perform within the good contract would verify whether or not the person has deposited Ether within the contract. 

The contract would verify the stability mapping of the involved handle and make sure that it’s higher than zero. Subsequently, the contract would verify whether or not the present time has exceeded the ‘lockTime’. If customers try and name the withdrawal perform earlier than one week, then it could fail the important verify for withdrawal. Such sorts of contracts are weak to integer overflow assaults as malicious actors may assign a big quantity to the ‘lockTime’ variable within the contract. How can hackers assault the ‘TimeLock’ contract?

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Steps for Compromising the TimeLock Contract

The next contract instance has been used to show the working mechanism of integer overflow. 

contract TimeLock {

    mapping(handle => uint) public balances;

    mapping(handle => uint) public lockTime;

    perform deposit() exterior payable {

        balances[msg.sender] += msg.worth;

        lockTime[msg.sender] = now + 1 weeks;


    perform increaseLockTime(uint _secondsToIncrease) public {

        lockTime[msg.sender] += _secondsToIncrease;


    perform withdraw() public {

        require(balances[msg.sender] > 0);

        require(now > lockTime[msg.sender]);

        balances[msg.sender] = 0;




The time-locking contract serves as a time vault. It may present an evidence for “What is integer overflow attack?” by showcasing methods for compromising the overflow vulnerability. Assume that one of the customers has handy over their personal key forcefully. In such circumstances, the ‘TimeLock’ contract can make sure that the Ether of their contract shouldn’t be retrievable for at the least one week. However, customers who’ve greater than 100 Ether within the contract and have handy their keys to a hacker might be victims of an integer overflow assault. 

Hackers may discover out the present ‘lockTime’ parameter for the involved handle that they know. First of all, the attacker may name the ‘increaseLockTime’ perform and cross the next quantity for the ‘userLockTime.’ It might result in the overflow and reset the lockTime to zero. Subsequently, the attacker may solely name the withdraw perform to steal their reward.

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What are the Different Situations for Integer Overflow?

You shouldn’t depend on just one instance of the ‘TimeLock’ contract for understanding integer overflow. However, you have to search for one other integer overflow assault instance that helps you establish different eventualities the place you’ll be able to anticipate integer overflow. One of the foremost examples of such eventualities would level to the presence of a perform within the good contract that doesn’t search for integer underflow. As well as, it’s also possible to encounter integer overflow points because of illustration of an array’s size as an unsigned integer. 

One other instance of a state of affairs for increased potentialities of integer overflow factors at a single transaction overflow. Single transaction overflows are the widespread highlights in conditions the place multiplication of two signed integers results in an unsigned integer because the output. In some circumstances, you’ll be able to encounter the integer overflow Solidity contracts can have because of an integer overflow bug. Such sorts of bugs in problematic code for various ERC-20 token contracts may permit a token holder to ship tokens to totally different recipients. 

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What are the Well-liked Examples of Overflow Attacks?

The most important spotlight in a dialogue about an integer overflow assault is the listing of examples for the assault. It is very important find out about “What is integer overflow attack?” by referring to in style examples of overflow assaults. Right here is an overview of some of the favored examples of good contract exploits with overflow assaults. 

The ‘BeautyChain’ contract is a well-liked instance of an overflow assault on a sensible contract when the attacker utilized the vulnerability to beat safety assessments. However, you must also know that the good contract vulnerability led to the loss of an enormous quantity of native tokens. 

The subsequent essential integer overflow assault instance is the Proof of Weak Arms Coin. It’s a sort of Ponzi scheme on Ethereum, programmed in Solidity language. The good contract builders didn’t observe the vulnerabilities for overflow or underflow and misplaced 866 ETH from the contract. 

The instance of Coinstar or CSTR additionally showcases one other outstanding purpose why it is best to keep protected from integer overflow. You should know that the ‘mintToken’ perform of the good contract had an integer overflow vulnerability. The difficulty emerged from the vulnerability that might empower the good contract for establishing the stability of random customers to any worth. 

How Can You Detect Integer Overflow and What are the Challenges?

The foremost problem with EVM is that it doesn’t present any notification for integer overflow. It’s a widespread function in a number of programming languages. It is best to know that overflow occurs because of storage of values after transactions. One of the best ways to establish the chance of overflow is to rerun the transaction. 

Arithmetic operations are additionally one of essentially the most notable causes of integer overflow assaults, as addition or subtraction of two numbers may result in the vulnerability. As well as, multiplication and exponent operations are straight associated to addition, thereby resulting in potentialities of overflow. 

The info sorts for signed and unsigned integers are declared solely in high-level programming languages. Nevertheless, the identical shouldn’t be relevant to byte code stage. Subsequently, you would not discover the Solidity supply code, thereby creating difficulties for guessing the kind of integers. 

Finest Practices for Resolving Overflow Dangers

Good contract builders may resolve the dangers of integer overflow by following totally different strategies, akin to checking the compiler model. You may resolve the integer overflow good contract vulnerability by utilizing the SafeMath library or appropriate information sorts for detecting overflows. The SafeMath library gives insights on preconditions and post-conditions for figuring out the chance of an overflow. Within the occasion of an error, the SafeMath library may end in transaction failure and revert the updates in transaction standing. 

One other trusted greatest observe for avoiding the integer overflow assault is to maintain your code up to date repeatedly with out potential vulnerabilities. Builders must also verify that the Solidity compiler model have to be 0.8 or increased. The upper compiler variations make sure that the preventive code of SafeMath library is built-in into the compiled code.

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Backside Line

The introduction to integer overflow assaults exhibits that good contract safety dangers can emerge from trivial vulnerabilities. Integer overflow is clear in eventualities the place the outcomes of the calculation may exceed the vary of specified information sort. The instance of ‘TimeLock’ contract and the simplicity of implementing the overflow assault present that anybody may exploit good contracts. It is best to perceive the different sorts of eventualities that might result in integer overflow for preventing in opposition to the vulnerability. Be taught extra about different good contract vulnerabilities and the way they have an effect on web3 adoption now.          

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