GHSA-m2v9-w374-5hj9

### Summary Prior to v0.3.0, `__default__()` functions did not respect the `@nonreentrancy` decorator and the lock was not emitted. This is a known bug and was already visible in the issue tracker (https://github.com/vyperlang/vyper/issues/2455), but it is being re-issued as an advisory so that tools relying on the advisory publication list can incorporate it into their searches. A contract search was additionally performed and no vulnerable contracts were found in production. ### PoC ```vyper @external @payable @nonreentrant("default") def __default__(): pass ``` after codegen: ``` [seq, [if, [lt, calldatasize, 4], [goto, fallback]], [mstore, 28, [calldataload, 0]], [with, _func_sig, [mload, 0], seq], [seq_unchecked, [label, fallback], [seq, pass, # Line 5 pass, pass, # Line 4 stop]]], ``` ### Impact No vulnerable production contracts were found. Additionally, using a lock on a `default` function is a very sparsely used pattern. As such, the impact is `low`.