GHSA-r53p-7pc4-xj5r undici vulnerable to downstream response splitting via retry interceptor

• npm undici: < 6.28.1 → fixed in 6.28.1 • npm undici: >= 7.0.0, < 7.29.1 → fixed in 7.29.1 • npm undici: >= 8.0.0, < 8.10.2 → fixed in 8.10.2

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 one of these or later. Workarounds • Disable `interceptors.retry()` for untrusted upstreams, or set `maxRetries: 0`. • Remove or recalculate `Content-Length` before forwarding a response body assembled by Undici.