{"id":"GHSA-r53p-7pc4-xj5r","summary":"undici vulnerable to downstream response splitting via retry interceptor","details":"### Impact\n\nUndici's `interceptors.retry()` can resume a request after a partial response and append the resumed bytes to an already partially delivered body, while the application still receives the original response's status and headers. When that response carried a `Content-Length`, the application can receive a longer body. Applications that forward Undici's status, headers, and body downstream without recalculating framing, for example proxy or gateway applications, may emit a response whose body exceeds the forwarded `Content-Length`, and the excess bytes can be read as the start of a subsequent HTTP response (downstream response splitting or desynchronization).\n\nFor example, a `404 Not Found` with `Content-Length: 2` that sends one byte then closes can be resumed with an open-ended `Range` request, and the resumed `206 Partial Content` bytes are appended, so the application receives more than two body bytes while still seeing `Content-Length: 2`. The bug requires `interceptors.retry()` enabled, an attacker-controlled or faulty upstream, and a downstream forwarder that does not recalculate `Content-Length`.\n\n### Patches\n\nPatched in undici v6.28.1, v7.29.1, and v8.10.2. Upgrade to one of these or later.\n\n### Workarounds\n\n- Disable `interceptors.retry()` for untrusted upstreams, or set `maxRetries: 0`.\n- Remove or recalculate `Content-Length` before forwarding a response body assembled by Undici.","aliases":["CVE-2026-18540"],"modified":"2026-09-29T18:30:41.154532067Z","published":"2026-09-29T18:22:07Z","database_specific":{"nvd_published_at":"2026-09-04T18:17:50Z","cwe_ids":["CWE-444"],"severity":"LOW","github_reviewed":true,"github_reviewed_at":"2026-09-29T18:22:07Z"},"references":[{"type":"WEB","url":"https://github.com/nodejs/undici/security/advisories/GHSA-r53p-7pc4-xj5r"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-18540"},{"type":"WEB","url":"https://github.com/nodejs/undici/commit/0160a719063fb0a77f4fdf9500b9166b91e14329"},{"type":"WEB","url":"https://github.com/nodejs/undici/commit/cd8af90b38ae33c2838d54a2d629774122effe95"},{"type":"WEB","url":"https://github.com/nodejs/undici/commit/ce31bc824b578008faae5d3350da66c1b5f71548"},{"type":"WEB","url":"https://hackerone.com/reports/3900104"},{"type":"WEB","url":"https://hackerone.com/reports/3900615"},{"type":"WEB","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"PACKAGE","url":"https://github.com/nodejs/undici"},{"type":"WEB","url":"https://github.com/nodejs/undici/releases/tag/v6.28.1"},{"type":"WEB","url":"https://github.com/nodejs/undici/releases/tag/v7.29.1"},{"type":"WEB","url":"https://github.com/nodejs/undici/releases/tag/v8.10.2"}],"affected":[{"package":{"name":"undici","ecosystem":"npm","purl":"pkg:npm/undici"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"6.28.1"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-r53p-7pc4-xj5r/GHSA-r53p-7pc4-xj5r.json"}},{"package":{"name":"undici","ecosystem":"npm","purl":"pkg:npm/undici"},"ranges":[{"type":"SEMVER","events":[{"introduced":"7.0.0"},{"fixed":"7.29.1"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-r53p-7pc4-xj5r/GHSA-r53p-7pc4-xj5r.json"}},{"package":{"name":"undici","ecosystem":"npm","purl":"pkg:npm/undici"},"ranges":[{"type":"SEMVER","events":[{"introduced":"8.0.0"},{"fixed":"8.10.2"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-r53p-7pc4-xj5r/GHSA-r53p-7pc4-xj5r.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N"}]}