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@yuriy77k
Created Mar 20, 2019
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Binance token (BNB) Audit Report.

Security Audit Report

1. Summary

Binance token (BNB) smart contract security audit report performed by Callisto Security Audit Department

2. In scope

bnb.sol

3. Findings

In total, 5 issues were reported including:

  • 5 low severity issues.

No critical security issues were found.

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. ERC20 Compliance — event missing

Severity: low

Description

  1. According to ERC20 standard when coins are minted a Transfer event should be emitted.

  2. There is no Approval event call at approve function. And EIP20 says:

MUST trigger on any successful call to approve(address _spender, uint256 _value).

  1. The burn function also should emit the Transfer event.

Code snippet

  1. initial supply
  2. Approval event
  3. burn function and Transfer event

3.3. ERC20 Compliance — zero-value transfers rejecting

Severity: low

Description

EIP20 says that:

Transfers of 0 values MUST be treated as normal transfers and fire the Transfer event. But in this contract, function transfer has a condition:

if (_value <= 0) throw;

Code snippet

3.4. ERC20 Compliance — approve issues

Severity: low

Code snippet

Description

  1. There is no way to reset approved value to 0, because approve function contains:
if (_value <= 0) throw; 
  1. Also it breaks the EIP20 security recommendation:

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

3.5. Fallback Function

Severity: low

Description

Any ether sent directly to the contract through the fallback function will not result in an automatic buy of tokens but instead is directly sent to the contract balance.

Code snippet

https://gist.github.com/yuriy77k/7612e9b1f915f169542e711dd6a29166#file-bnb-sol-L144

4. Conclusion

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

5. Revealing audit reports

https://gist.github.com/yuriy77k/b228e8df2aa47aef84e91423dd340894

https://gist.github.com/yuriy77k/ee463004023c4caee3b36bea30deb32f

https://gist.github.com/yuriy77k/b15d652f64211b51711f0648cdab6000

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