Pundi X

Pundi X (NPXS) Security Audit Report

Here is the report of the Pundi X (NPXS) Security Audit performed by the Callisto Network security department in June 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.

Pundi X (NPXS) specificities

Source code


Disclosure policy




Number of lines


Pundi X (NPXS) Security Audit Report

1. Summary

Pundi X (NPXS) Token smart contract security audit report performed by Callisto Security Audit Department

2. In scope

  1. NPXSToken.sol

3. Findings

In total, 9 issues were reported including:

  • 5 low severity issues.
  • 1 notes.
  • 3 owner privileges (the ability of an owner to manipulate contract, may be risky for investors).

No critical security issues were found.

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

require( _to != address(this) );

3.2. Owner Privileges

Severity: owner privileges


  1. The owner receives funds immediately after the purchase of tokens. It should be available after the end of crowdsale. Otherwise, the owner has the opportunity to buy tokens for the same money. (line 149). RefundVault and WithdrawVault contracts is managed manually by the owner and are not integrated with the Crowdsale contract which is not good for investors. (lines 200 and 446)
  2. The contract owner allowed to pause transfer functions (transfer, transferFrom). (lines 541-545)
  3. The owner can finish minting whenever he wants. Related with issue #4. (line 401)

3.3. ERC20 Compliance: event missing

Severity: low


According to ERC20 standard when burning coins a transfer event should be emitted. In this case the Burn event is emitted, it is better to additionally use emit Transfer(msg.sender, address(0), value);

Code snippet

3.4. stopReceive is not implemented for transferFrom

Severity: low


stopReceive mechanism is used for transfer function but not implemented for transferFrom function. It is possibler to approve funds to yourself and send through transferForm without any restrictions.

Code snippet

3.5. ERC223 Compliance, transferAndCall issues

Severity: note


  1. Judging by the call of the tokenFallback function, this token should support the ERC223 standard. But in this case it should be called in the transfer function also. It should check whether the recipient is a contract. And function transfer(address, uint, bytes) should be implemented. Please, read this
  2. Judging by transferAndCall function this token should support the ERC677 standard. But in this case it should call contractFallback not tokenFallback function. And should check whether the recipient is a contract. Please, read this
  3. transferAndCall function does not use whenNotPaused modifier and tokens may be transferred even if the contract is paused.

Code snippet

3.6. Zero address checking

Severity: low


There are no zero address checking in functions deposit at line 212, mint at line 389, deposit at line 465

3.7. Allowance Approval

Severity: low


Following ERC-20 final description:

“NOTE: To prevent attack vectors like the one described here and discussed here, clients SHOULD make sure to create user interfaces in such a way that they set the allowance first to 0 before setting it to another value for the same spender. THOUGH The contract itself shouldn’t enforce it, to allow backwards compatibility with contracts deployed before.

Do not throw in case if the following condition is true require((value == 0) || (_allowances[msg.sender][spender] == 0)) and return false, users might not notice that the changes didn’t occur, and external contract calls to this function will highlight many other issues.

Code snippet

function approve(address _spender, uint256 _value) returns (bool) {

    require((_value == 0) || (allowed[msg.sender][_spender] == 0));

    allowed[msg.sender][_spender] = _value;
    Approval(msg.sender, _spender, _value);
    return true;

4. Conclusion

The audited smart contract can be deployed. Only low severity issues were found during the audit.

5. Revealing audit reports