undici vulnerable to downstream response desynchronization via retry interceptor

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

4.8 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

EPSS

• CVE-2026-16728: 0.29% estimated exploitation activity in the next 30 days; percentile 21.41 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact Undici's interceptors.retry() can deliver a response whose body length does not match the Content-Length header exposed to the application after a retry or resume of a partial response. Applications that use interceptors.retry() and forward upstream response headers and bodies downstream, for example proxy or gateway applications, may emit an invalid HTTP response with a stale Content-Length header. This can lead to downstream response desynchronization, connection hangs, or response corruption in clients or intermediaries that rely on the forwarded framing metadata. A malicious or faulty upstream can respond to a range request with a 206 Partial Content response such as: and then send only 99 bytes before closing the socket. interceptors.retry() can then retry with Range: bytes=99-99, receive the final byte, and deliver a 100-byte body to the application while the response headers still contain Content-Length: 300 from the first response. The bug requires interceptors.retry()…

Published by the source

3 Aug 2026, 19:24 UTC

Last modified by the source

3 Aug 2026, 19:24 UTC

Source last checked

26 Oct 2026, 13:00 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-8xcm-r25x-g524

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# Patch Next advisory brief: CVE-2026-16728

Advisory: undici vulnerable to downstream response desynchronization via retry interceptor
IDs: CVE-2026-16728, GHSA-8xcm-r25x-g524
Record: https://patchnext.com/advisories/cve-2026-16728 (revision 1, source checked 26 Oct 2026, 13:00 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: undici 8.9.0, 7.29.0, 6.28.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm undici: affected < 6.28.0; >= 7.0.0, < 7.29.0; >= 8.0.0, < 8.9.0; fixed in 6.28.0, 8.9.0, 7.29.0

## Suggested inspection (read-only)
- `npm ls undici --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on undici.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-8xcm-r25x-g524 (GitHub-reviewed advisory GHSA-8xcm-r25x-g524 lists affected ranges: npm undici >=0 =7.0.0 =8.0.0 <8.9.0)

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