# No support for fee on transfer tokens Crit/High · Three Sigma · Private DeFi access · 26th February, 2024 Finding 3S-SG-M04 of the Singularity security review. - Protocol: https://www.thesingularity.network/ - Report: /reports/singularity - Source: https://cdn.sanity.io/files/qoqld077/production/45b8aac56a2b8e3b557df4329ac9bf8220b64012.pdf --- ### Description Fee on transfer tokens are not correctly dealt, as the transferFrom() call is expected to transfer exactly the requested amount. However, this is not the case for tokens that charge a fee on transfer. ### Recommendation To support these tokens, check the balance before calling safeTransferFrom() and compare with the new balance, getting the actual transferred amount. ### Status Acknowledged --- Related findings: - [Fee on transfer tokens transfer less tokens than what is stored in the receipt on deposits](https://0xsimao.com/findings/clip-finance-i-fee-transfer-receipt-deposits): Clip Finance Strategies - [BasicVault is incompatible with fee-on-transfer tokens](https://0xsimao.com/findings/mitosis-basic-incompatible-fee-transfer): Mitosis - [`LenderCommitmentGroup` pools will have incorrect exchange rate when fee-on-transfer tokens are used](https://0xsimao.com/findings/teller-finance-pools-exchange-fee-transfer): Teller Finance - [Halted withdrawals in BatchOut:withdrawFulfill() due to tokens transfer() reverting on 0 transfer amount](https://0xsimao.com/findings/clip-finance-i-halted-withdrawals-withdraw-transfer): Clip Finance Strategies