{"id":"CVE-2026-19481","aliases":["GHSA-x8mw-p69m-v3mx"],"url":"https://o3.security/vulnerability/CVE-2026-19481","summary":"@fastify/busboy vulnerable to Denial of Service via prototype-named multipart part header","details":"### Impact\n\nVersions of `@fastify/busboy` from 1.0.0 and prior to 3.2.1 are vulnerable to a Denial of Service. The multipart header parser stores part-header names on a plain JavaScript object, so a part header named `__proto__` or `constructor` resolves to an inherited value that is not an array, and the parser throws `TypeError: this.header[h].push is not a function`. Through the documented `req.pipe(busboy)` integration this surfaces as an `error` event, while direct `write()`/`end()` usage throws synchronously and can terminate the Node.js process if uncaught. The parser runs before application middleware, so any unauthenticated client that can submit multipart/form-data is affected.\n\n### Patches\n\nFixed in version 3.2.1.\n\n### Workarounds\n\nAttach an `error` listener to the Busboy stream so the parser failure is handled rather than crashing the process, and wrap direct `write()`/`end()` calls in a try/catch. Upgrading to 3.2.1 removes the failure entirely.","published":"2026-08-13T08:31:25.413Z","modified":"2026-10-21T02:56:18.722852706Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":{"score":0.00278,"percentile":0.20382,"asOf":"2026-09-16"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"@fastify/busboy","fixedVersion":"3.2.1"}],"fix":{"url":"https://github.com/fastify/busboy/commit/957a24b66d5915e6d0a6ac988c9dbcee86373e9b","label":"fastify/busboy@957a24b"},"references":[{"type":"ADVISORY","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/19xxx/CVE-2026-19481.json"},{"type":"ADVISORY","url":"https://github.com/fastify/busboy/security/advisories/GHSA-x8mw-p69m-v3mx"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-19481"},{"type":"WEB","url":"https://github.com/fastify/busboy/commit/957a24b66d5915e6d0a6ac988c9dbcee86373e9b"},{"type":"PACKAGE","url":"https://github.com/fastify/busboy"},{"type":"WEB","url":"https://github.com/fastify/busboy/releases/tag/v3.2.1"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:56:18.722852706Z"}}