Idex Security Audit Report

Here is the report of the Idex Security Audit performed by the Callisto Network security department in May 2019.

About Callisto Network and the security department

Utilizing Callisto Network capabilities, we have established a free-for-all system of smart-contracts auditing, to this end, Callisto Network has founded the Callisto security department and deploys treasury funds to pay security auditors for auditing smart-contracts, to reduce risk/flaw in smart-contracts and improve the adoption of programmable blockchains for the whole crypto industry.

Idex specificities

Source code

Disclosure policy


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Idex Security Audit Report

1. Summary

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

2. In scope

Сommit hash 4a05eb28e570e9820066474ff2adc924ce7a27bd.

3. Findings

In total, 4 issues were reported including:

  • 1 medium severity issues.
  • 3 low severity issues.

3.1. ERC20 Compliance: transfer function returns nothing

Severity: medium


ERC-20 Token Standard specifies for function transfer.
The current convention is for ERC20 tokens to revert if there’s an error and return true if there isn’t, because this is safest should work for everyone.
But in this implementation transfer function returns 0 bytes is violating the ERC20 interface.

The biggest risk is that a smart contract that is compiled with solc ≥ 0.4.22 , which is expecting an ERC20 interface, will not be able to interact with MyTokens. This could mean that tokens which are send to such a contract, will be stuck there forever even if the contract has a function to transfer ERC20 token. There are many different scenarios where contracts, handling ERC20 tokens would run into this bug. One example is, that you would not be able to use decentralized exchanges that compiled its contract with solc ≥ 0.4.22 with this implementation of MyToken.
More details here.

Code snippet

3.2. Known vulnerabilities of ERC-20 token

Severity: low


  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.


Add into a function transfer(address _to, ... ) following code:

require( _to != address(this) );

3.3. ERC20 Compliance

Severity: low


According to ERC20 standard, when initializing a token contract if any token value is set to any given address a transfer event should be emitted.

Code snippet

3.4. Check for an empty input value

Severity: low


There is no check for an empty input value.

Code snippet

3.5. Deprecated method

Severity: minor observation


The function () { throw; } was a pattern used to prevent implicit acceptance of ether in Solidity versions older than 0.4.0, but today this is unneeded.

Code snippet

4. Conclusion

The audited smart contract must not be deployed. Reported issues must be fixed prior to the usage of this contract.

5. Revealing audit reports