undici vulnerable to downstream response splitting via retry interceptor
### 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.
GHSA-r53p-7pc4-xj5r
Primary source · Revision 1
Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.
Security context
Source reference: osv:GHSA-r53p-7pc4-xj5r
undici
Source reference: /affected/0/package/name
- Affected versions
- Not stated in this record
- Fixed versions
- 6.28.1
Source reference:
/affected/0/ranges - Prerequisites
- Not stated in this record
undici
Source reference: /affected/1/package/name
- Affected versions
- Not stated in this record
- Fixed versions
- 7.29.1
Source reference:
/affected/1/ranges - Prerequisites
- Not stated in this record
undici
Source reference: /affected/2/package/name
- Affected versions
- Not stated in this record
- Fixed versions
- 8.10.2
Source reference:
/affected/2/ranges - Prerequisites
- Not stated in this record
Structured affected-version data
Original package identities and version rules from this source.
[
{
"ranges": [
{
"type": "SEMVER",
"events": [
{
"introduced": "0"
},
{
"fixed": "6.28.1"
}
]
}
],
"package": {
"name": "undici",
"purl": "pkg:npm/undici",
"ecosystem": "npm"
},
"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"
}
},
{
"ranges": [
{
"type": "SEMVER",
"events": [
{
"introduced": "7.0.0"
},
{
"fixed": "7.29.1"
}
]
}
],
"package": {
"name": "undici",
"purl": "pkg:npm/undici",
"ecosystem": "npm"
},
"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"
}
},
{
"ranges": [
{
"type": "SEMVER",
"events": [
{
"introduced": "8.0.0"
},
{
"fixed": "8.10.2"
}
]
}
],
"package": {
"name": "undici",
"purl": "pkg:npm/undici",
"ecosystem": "npm"
},
"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"
}
}
]- Related CVEs
- CVE-2026-18540
Source reference:
/aliases
Publisher severity
low
Source reference: /database_specific/severity
- Event
- #31150 · Revision 1
- Added to Heist Feed
- Publisher date