Skip to content
medium Token Standards SWC-114 CWE-362

ERC-20 Approval Race Condition

SAFE-0050 Token Standards Checked automatically by the scanner
1

What goes wrong

Changing an existing non-zero allowance with approve() lets a spender front-run the change and spend both the old and new allowance.

2

How to fix it

the pattern that is safe
token.safeIncreaseAllowance(spender, delta);
// or: approve(spender,0); approve(spender,newValue);
◆
Known ERC-20 approve race. Use increase/decreaseAllowance.
3

Related vulnerabilities in Token Standards

SAFE-0053Unsafe / Unprotected Minting critical · Token Standards SAFE-0051Missing SafeERC20 / Non-Standard Token Handling high · Token Standards SAFE-0052Fee-on-Transfer / Rebasing Token Accounting Mismatch high · Token Standards SAFE-0055Burn Authorization / Burn-From Missing Checks high · Token Standards SAFE-0107Fee-on-Transfer / Rebasing Token Mis-Accounting high · Token Standards SAFE-0208Non-Standard ERC20 Return Value Not Handled high · Token Standards SAFE-0054ERC-721/1155 Missing Receiver Validation (Safe Transfer) medium · Token Standards SAFE-0056EIP-2612 Permit Misuse / Front-Running medium · Token Standards
← PreviousMerkle Proof Validation Error
Check your own contract for this

The SaferICO scanner runs 201 detectors over your Solidity source, SAFE-0050 among them. Paste an address or the source itself — a small per-scan fee, shown before you sign, or unlimited on any plan.

Run the scanner See how it is attacked Read the docs