{"id":"CVE-2025-47285","summary":"Vyper's `concat()` builtin may elide side-effects for zero-length arguments","details":"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.","aliases":["GHSA-qhr6-mgqr-mchm"],"modified":"2026-04-10T05:28:46.056163Z","published":"2025-05-15T17:24:03.442Z","database_specific":{"cwe_ids":["CWE-691"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/47xxx/CVE-2025-47285.json","cna_assigner":"GitHub_M"},"references":[{"type":"WEB","url":"https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/builtins/functions.py#L560-L562"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/47xxx/CVE-2025-47285.json"},{"type":"ADVISORY","url":"https://github.com/vyperlang/vyper/security/advisories/GHSA-qhr6-mgqr-mchm"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-47285"},{"type":"FIX","url":"https://github.com/vyperlang/vyper/pull/4644"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/vyperlang/vyper","events":[{"introduced":"0"},{"last_affected":"11522b836bd0d86cf43ec186aa3b2b8e986ca4fe"}],"database_specific":{"versions":[{"introduced":"0"},{"last_affected":"0.4.2rc1"}]}}],"versions":["0.2.1","pre-release","v0.0.4","v0.1.0-beta.1","v0.1.0-beta.10","v0.1.0-beta.11","v0.1.0-beta.12","v0.1.0-beta.13","v0.1.0-beta.14","v0.1.0-beta.15","v0.1.0-beta.16","v0.1.0-beta.17","v0.1.0-beta.2","v0.1.0-beta.3","v0.1.0-beta.5","v0.1.0-beta.6","v0.1.0-beta.7","v0.1.0-beta.8","v0.1.0-beta.9","v0.2.0","v0.2.1","v0.2.10","v0.2.11","v0.2.12","v0.2.13","v0.2.14","v0.2.15","v0.2.16","v0.2.2","v0.2.3","v0.2.4","v0.2.5","v0.2.6","v0.2.7","v0.2.8","v0.2.9","v0.3.0","v0.3.1","v0.3.10","v0.3.10rc1","v0.3.10rc2","v0.3.10rc3","v0.3.10rc4","v0.3.10rc5","v0.3.2","v0.3.3","v0.3.4","v0.3.5","v0.3.6","v0.3.7","v0.3.8","v0.3.9","v0.4.0","v0.4.0b1","v0.4.0b2","v0.4.0b3","v0.4.0b4","v0.4.0b5","v0.4.0b6","v0.4.0rc1","v0.4.0rc2","v0.4.0rc3","v0.4.0rc4","v0.4.0rc5","v0.4.0rc6","v0.4.1","v0.4.1b1","v0.4.1b2","v0.4.1b3","v0.4.1b4","v0.4.1rc1","v0.4.1rc2","v0.4.1rc3","v0.4.2rc1"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-47285.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V4","score":"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"}]}