SENDER == SELF_ADDRESS is externally inducible

On Etherlink, an external party can make a contract observe its immediate caller as its own address on a bare value transfer. A Michelson contract can be made to see SENDER == SELF_ADDRESS, and an EVM contract can be made to see msg.sender == address(this), without any cooperation from the target: by sending tez to the contract's EVM alias, or Michelson alias, respectively.

This is a consequence of the alias forwarding design, not a contract bug. Any authorization that trusts caller-equals-self as an internal only signal must not be relied upon on Etherlink.

What this means for developers

When developing smart contracts, keep in mind the following:

• Do not use SENDER == SELF_ADDRESS in Michelson, or msg.sender == address(this) in Solidity, as a trusted internal only or authorization signal on the default entrypoint or the value receiving fallback.
• A contract correct on Tezos L1 that gates a privileged default entrypoint action on caller-equals-self is silently reachable by any external party on Etherlink. Move such gates to a named entrypoint or to an explicit authorization check on a recorded controller.
• The originator identity is unaffected: SOURCE in Michelson and tx.origin in Solidity still reflect the external party that initiated the transfer, so guards keyed on the originator remain meaningful.