SPL Token Authority Confusion Remediation

Overview

Related Detector: SPL Token Authority Confusion

Authority confusion occurs when a program checks the wrong authority for a token operation – for example, validating owner but performing a close that requires close_authority, or using Transfer instead of TransferChecked. The fix requires matching each operation to its correct authority and using checked instruction variants.

Recommended Fix

Before (Vulnerable)

// Uses Transfer (no decimal check) and doesn't verify authority
let ix = spl_token::instruction::transfer(
    &spl_token::id(), source.key, dest.key, authority.key, &[], amount,
)?;
invoke(&ix, accounts)?;

After (Fixed)

// Verify authority signed
if !authority.is_signer {
    return Err(ProgramError::MissingRequiredSignature);
}

// Use TransferChecked for decimal validation
let ix = spl_token::instruction::transfer_checked(
    &spl_token::id(), source.key, mint.key, dest.key,
    authority.key, &[], amount, expected_decimals,
)?;
invoke(&ix, &[source.clone(), mint.clone(), dest.clone(), authority.clone()])?;

Alternative Mitigations

1. Anchor typed accounts

#[derive(Accounts)]
pub struct Transfer<'info> {
    #[account(mut, token::authority = authority)]
    pub source: Account<'info, TokenAccount>,
    #[account(mut)]
    pub destination: Account<'info, TokenAccount>,
    pub authority: Signer<'info>,
    pub token_program: Program<'info, Token>,
}

the account-validation framework’s token::authority constraint validates the correct authority at deserialization.

2. Explicit authority type matching

For operations that can use either owner or delegate, explicitly check which authority type is provided:

let token_data = Account::unpack(&token_account.data.borrow())?;
if *authority.key == token_data.owner {
    // Owner transfer -- full balance available
} else if token_data.delegate == COption::Some(*authority.key) {
    // Delegated transfer -- limited to delegated_amount
    require!(amount <= token_data.delegated_amount, InsufficientDelegation);
} else {
    return Err(ProgramError::InvalidAccountData);
}

Common Mistakes

Mistake 1: Using Transfer instead of TransferChecked

// WRONG: Transfer does not validate decimals
spl_token::instruction::transfer(...)?;
// CORRECT: TransferChecked validates decimal precision
spl_token::instruction::transfer_checked(..., amount, decimals)?;

Mistake 2: Confusing mint_authority with freeze_authority

// WRONG: using freeze_authority to mint tokens
// mint_authority and freeze_authority are different fields on the Mint account

Mistake 3: Using owner for close when close_authority is set

// WRONG: if close_authority is set, owner cannot close
// Must check: if token_account.close_authority.is_some(), use that authority