IOSToken Audit Report.

ETH_IOSToken_report.md

Security Audit Report

1. Summary

IOSToken smart contract security audit report performed by Callisto Security Audit Department

Token desription:

Symbol      : IOST
Name        : IOSToken
Total supply: 21,000,000,000
Decimals    : 18 
Standard    : ERC20

2. In scope

• IOSToken.sol

3. Findings

In total, 4 issues were reported including:

• 1 medium severity issues.

• 3 low severity issues.

3.1. Known vulnerabilities of ERC-20 token

Severity: low

Description

1. It is possible to double withdrawal attack. More details here.

2. Lack of transaction handling mechanism issue. WARNING! This is a very common issue and it already caused millions of dollars losses for lots of token users! More details here.

Recommendation

Add the following code to the transfer(_to address, ...) function:

require( _to != address(this) );

3.2 Non-compliance with ERC-20 Token Standard.

Severity: medium

Description

ERC-20 Token Standard specifies for functions transfer and transferFrom:

The function SHOULD throw if the _from account balance does not have enough tokens to spend. But in this implementation it just returns false. This can lead to serious consequences. Because checking the return value of this function is rare.

Code snippet

https://gist.github.com/yuriy77k/164e096306a2b117b68b4cf9cca9f756#file-iostoken-sol-L60

https://gist.github.com/yuriy77k/164e096306a2b117b68b4cf9cca9f756#file-iostoken-sol-L70

https://gist.github.com/yuriy77k/164e096306a2b117b68b4cf9cca9f756#file-iostoken-sol-L108

3.3. Transfer to address(0)

Severity: low

Description

Transfer to address(0) is allowed when using transfer or transferFrom functions.

Code snippet

https://gist.github.com/yuriy77k/164e096306a2b117b68b4cf9cca9f756#file-iostoken-sol-L60

https://gist.github.com/yuriy77k/164e096306a2b117b68b4cf9cca9f756#file-iostoken-sol-L70

Recommendation

Add zero address checking

require( _to != address(0) );

3.4. Unlimited Allowance

Severity: low

Description

Even if the likelihood of such issue to represent a risk for users is very low, the reimplemented transferFrom with unlimited allowance to an address is not complaint with ERC-20 standard. Users should be aware of it.

Code snippet

https://gist.github.com/yuriy77k/164e096306a2b117b68b4cf9cca9f756#file-iostoken-sol-L108

4. Conclusion

The audited smart contract has some issues with ERC20 Compliance that could cause losing the money in a particular situation. We recommend fixing these issues.

5. Revealing audit reports

https://gist.github.com/yuriy77k/ce4b26e2d0076584717ba0d083095d4e

https://gist.github.com/yuriy77k/9ac93e4cb81d884b85edb355ab7948e1

https://gist.github.com/yuriy77k/78729a1cad92e731b3ab77e884e9deee