{"cve":"CVE-2025-47285","nvd":{"published":"2025-05-15T18:15:38.177","modified":"2026-06-17T09:27:40.103","status":"Deferred","description":"Vyper is the Pythonic Programming Language for the Ethereum Virtual Machine. In versions up to and including 0.4.2rc1, `concat()` may skip evaluation of side effects when the length of an argument is zero. This is due to a fastpath in the implementation which skips evaluation of argument expressions when their length is zero. In practice, it would be very unusual in user code to construct zero-length bytestrings using an expression with side-effects, since zero-length bytestrings are typically constructed with the empty literal `b\"\"`; the only way to construct an empty bytestring which has side effects would be with the ternary operator introduced in v0.3.8, e.g. `b\"\" if self.do_some_side_effect() else b\"\"`. The fix is available in pull request 4644 and expected to be part of the 0.4.2 release. As a workaround, don't have side effects in expressions which construct zero-length bytestrings.","cvss_v4":{"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P","score":2.9},"cvss_v3":null,"cwes":["CWE-691"],"references":["https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/builtins/functions.py#L560-L562","https://github.com/vyperlang/vyper/pull/4644","https://github.com/vyperlang/vyper/security/advisories/GHSA-qhr6-mgqr-mchm"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:01:57.636215869+00:00"},"epss":{"cve":"CVE-2025-47285","score":0.00464,"percentile":0.40208,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-qhr6-mgqr-mchm","url":"https://osv.dev/vulnerability/GHSA-qhr6-mgqr-mchm","summary":"Vyper's `concat()` builtin may elide side-effects for zero-length arguments","modified":"2026-07-07T17:56:14.307189784Z","packages":[{"ecosystem":"PyPI","name":"vyper","purl":"pkg:pypi/vyper","ranges":["<=0.4.2rc1"],"fixed":[]}]},{"id":"PYSEC-2026-2029","url":"https://osv.dev/vulnerability/PYSEC-2026-2029","summary":"Vyper's `concat()` builtin may elide side-effects for zero-length arguments","modified":"2026-07-07T17:47:20.266877349Z","packages":[{"ecosystem":"PyPI","name":"vyper","purl":"pkg:pypi/vyper","ranges":["<=0.4.2rc1"],"fixed":[]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}