Disclosure summary
### Impact Undici'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). For 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`. ### Patches Patched in undici v6.28.1, v7.29.1, and v8.10.2. Upgrade to
Source-specific records & product guidance
Sources retain their own attribution and scoring. Follow the original record to confirm affected versions, fixed releases, and configuration conditions.
GitHub Reviewed Security Advisories · GHSA-r53p-7pc4-xj5r
Open original source · Updated Sep 29, 2026
undici vulnerable to downstream response splitting via retry interceptor
Source severity: LOW / 0
| Ecosystem | Package | Affected range | First patched |
|---|---|---|---|
| npm | undici | < 6.28.1 | 6.28.1 |
| npm | undici | >= 7.0.0, < 7.29.1 | 7.29.1 |
| npm | undici | >= 8.0.0, < 8.10.2 | 8.10.2 |
Original records & references
- NIST NVD record
- CVE Program record
- github.com — Reviewed advisory
PUBLISHED 2026-09-29T14:22:07-04:00
MODIFIED 2026-09-29T14:22:08-04:00
INGESTED 2026-10-06T11:43:08-04:00