undici vulnerable to cookie attribute injection via unsanitized domain and unparsed setCookie fields

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-2026-16729: 0.28% estimated exploitation activity in the next 30 days; percentile 20.35 (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 The setCookie function has two attribute injection paths. validateCookieDomain does not reject semicolons (validateCookiePath already does at 0x3B), so a domain value like example.com; SameSite=None lands verbatim as Domain=example.com; SameSite=None. The unparsed array's loop only checks each entry contains = and does not sanitize values, so an entry like X-Custom=val; HttpOnly lands unchanged, injecting HttpOnly without the caller setting cookie.httpOnly = true. Applications that pass user-controlled input to these fields, typically multi-tenant or reverse-proxy servers that scope session cookies to a tenant-supplied domain, can have SameSite CSRF protections bypassed, Secure or HttpOnly forced or stripped, or the intended SameSite tier overridden. Patches Patched in undici v6.28.0, v7.29.0, and v8.9.0. Workarounds - Sanitize domain values against the RFC 1034 letter-digit-hyphen set before passing to setCookie. - Do not pass user-controlled data to the unparsed field.

Published by the source

3 Aug 2026, 19:30 UTC

Last modified by the source

3 Aug 2026, 19:30 UTC

Source last checked

26 Oct 2026, 13:00 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-v3r7-h72x-cjcm

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-16729

Advisory: undici vulnerable to cookie attribute injection via unsanitized domain and unparsed setCookie fields
IDs: CVE-2026-16729, GHSA-v3r7-h72x-cjcm
Record: https://patchnext.com/advisories/cve-2026-16729 (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-v3r7-h72x-cjcm (GitHub-reviewed advisory GHSA-v3r7-h72x-cjcm lists affected ranges: npm undici >=0 =7.0.0 =8.0.0 <8.9.0)

Commands are suggestions: review each one before running it.