{"id":"CVE-2025-47285","state":"PUBLISHED","title":"Vyper's `concat()` builtin may elide side-effects for zero-length arguments","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.","publishedAt":"2025-05-15T17:24:03.442Z","updatedAt":"2025-05-15T18:37:33.747Z","severity":{"score":2.9,"label":"Low","version":"4.0","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","source":"GitHub_M"},"assigner":"GitHub_M","products":["vyperlang vyper"],"affected":[{"vendor":"vyperlang","product":"vyper","versions":[{"version":"<= 0.4.2rc1","status":"affected"}]}],"references":["https://github.com/vyperlang/vyper/security/advisories/GHSA-qhr6-mgqr-mchm","https://github.com/vyperlang/vyper/pull/4644","https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/builtins/functions.py#L560-L562"],"weaknesses":["CWE-691"],"ingestedAt":"2026-10-29T20:09:23.771Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2025/47xxx/CVE-2025-47285.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.1","cveMetadata":{"cveId":"CVE-2025-47285","state":"PUBLISHED","datePublished":"2025-05-15T17:24:03.442Z","dateUpdated":"2025-05-15T18:37:33.747Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2025-05-05T16:53:10.374Z"},"containers":{"cna":{"title":"Vyper's `concat()` builtin may elide side-effects for zero-length arguments","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"vyperlang","product":"vyper","versions":[{"version":"<= 0.4.2rc1","status":"affected"}]}],"references":[{"url":"https://github.com/vyperlang/vyper/security/advisories/GHSA-qhr6-mgqr-mchm","name":"https://github.com/vyperlang/vyper/security/advisories/GHSA-qhr6-mgqr-mchm","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/vyperlang/vyper/pull/4644","name":"https://github.com/vyperlang/vyper/pull/4644","tags":["x_refsource_MISC"]},{"url":"https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/builtins/functions.py#L560-L562","name":"https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/builtins/functions.py#L560-L562","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV4_0":{"attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"PRESENT","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"LOW","vulnAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE","baseScore":2.9,"baseSeverity":"LOW","vectorString":"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","version":"4.0"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-691","lang":"en","description":"CWE-691: Insufficient Control Flow Management","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2025-05-15T17:24:03.442Z"},"source":{"advisory":"GHSA-qhr6-mgqr-mchm","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2025-05-15T18:37:27.011947Z","id":"CVE-2025-47285","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2025-05-15T18:37:33.747Z"}}]}}}