{"id":"CVE-2025-47774","aliases":["GHSA-3vcg-j39x-cwfm","PYSEC-2026-2028"],"url":"https://o3.security/vulnerability/CVE-2025-47774","summary":"Vyper's `slice()` may elide side-effects when output length is 0","details":"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.","published":"2025-05-15T17:38:58.487Z","modified":"2026-08-12T03:51:21.552908122Z","cvss":null,"epss":{"score":0.00459,"percentile":0.38927,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"vyper","fixedVersion":null}],"fix":{"url":"https://github.com/vyperlang/vyper/pull/4645","label":"vyperlang/vyper#4645"},"references":[{"type":"WEB","url":"https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/builtins/functions.py#L315-L319"},{"type":"WEB","url":"https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/codegen/core.py#L189-L191"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/47xxx/CVE-2025-47774.json"},{"type":"ADVISORY","url":"https://github.com/vyperlang/vyper/security/advisories/GHSA-3vcg-j39x-cwfm"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-47774"},{"type":"FIX","url":"https://github.com/vyperlang/vyper/pull/4645"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:21.552908122Z"}}