Description
Vyper is the Pythonic Programming Language for the Ethereum Virtual Machine. In versions up to and including 0.4.2rc1, the `slice()` builtin can elide side effects when the output length is 0, and the source bytestring is a builtin (`msg.data` or `<address>.code`). The reason is that for these source locations, the check that `length >= 1` is skipped. The result is that a 0-length bytestring constructed with slice can be passed to `make_byte_array_copier`, which elides evaluation of its source argument when the max length is 0. The impact is that side effects in the `start` argument may be elided when the `length` argument is 0, e.g. `slice(msg.data, self.do_side_effect(), 0)`. The fix in pull request 4645 disallows any invocation of `slice()` with length 0, including for the ad hoc locations discussed in this advisory. The fix is expected to be part of version 0.4.2.
Problem types
CWE-691: Insufficient Control Flow Management
Product status
References
github.com/.../vyper/security/advisories/GHSA-3vcg-j39x-cwfm
github.com/vyperlang/vyper/pull/4645
github.com/...74676170b8a6eaa316/vyper/builtins/functions.py
github.com/...312b4674676170b8a6eaa316/vyper/codegen/core.py