Possible reentrancy vulnerabilities. Avoid state changes after transfer SOLHINT-W1051

Possible reentrancy vulnerabilities. Avoid state changes after transfer.

Bad Practice

1. Vulnerable Contract 1

   pragma solidity 0.4.4;
    
   
    
   
     contract A {
    
   
               mapping(address => uint) private shares;
    
   
               function b() external {
                   uint amount = shares[msg.sender];
                   bool a = msg.sender.send(amount);
                   if (a) { shares[msg.sender] = 0; }
               }
    
   
     }
     

2. Vulnerable Contract 2

   pragma solidity 0.4.4;
    
   
    
   
     contract A {
    
   
               mapping(address => uint) private shares;
    
   
               function b() external {
                   uint amount = shares[msg.sender];
                   msg.sender.transfer(amount);
                   shares[msg.sender] = 0;
               }
    
   
     }
     

Recommended

1. Invulnerable Contract 1

   pragma solidity 0.4.4;
    
   
    
   
     contract A {
    
   
               mapping(address => uint) private shares;
    
   
               function b() external {
                   uint amount = shares[msg.sender];
                   shares[msg.sender] = 0;
                   msg.sender.transfer(amount);
               }
    
   
     }
     

2. Invulnerable Contract 2

   pragma solidity 0.4.4;
    
   
    
   
     contract A {
    
   
               mapping(address => uint) private shares;
    
   
               function b() external {
                   uint amount = shares[msg.sender];
                   user.test(amount);
                   shares[msg.sender] = 0;
               }
    
   
     }
     

3. Invulnerable Contract 3

   pragma solidity 0.4.4;
    
   
    
   
     contract A {
    
   
       function b() public {
    
   
               uint[] shares;
               uint amount = shares[msg.sender];
               msg.sender.transfer(amount);
               shares[msg.sender] = 0;
    
   
       }
    
   
     }
     

Learn more

reentrancy on Solhint's documentation.