MediumGHSA-v3r7-h72x-cjcmCVE-2026-16729

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

Published 3 Aug 2026 · Updated 10 Sept 2026

Affected packages

undicinpm
Affected
<6.28.0
Fixed in
6.28.0
Update to the fixed version for your release line, for example:npm install undici@6.28.0
undicinpm
Affected
>=7.0.0 <7.29.0
Fixed in
7.29.0
Update to the fixed version for your release line, for example:npm install undici@7.29.0
undicinpm
Affected
>=8.0.0 <8.9.0
Fixed in
8.9.0
Update to the fixed version for your release line, for example:npm install undici@8.9.0

Details

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.

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References

Advisory data from OSV.dev (opens OSV.dev in a new tab), refreshed daily.