Vulnerability · Published Jul 29, 2026 · Assigned by openjs
CVE-2026-16729undici vulnerable to cookie attribute injection via unsanitized domain and unparsed setCookie fields
Medium 4.8
In plain English
A medium-severity injection in undici from undici. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 20% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
undici's setCookie function does not fully sanitize cookie attributes. In undici before 6.28.0, from 7.0.0 up to before 7.29.0, and from 8.0.0 up to before 8.9.0, a domain value is not checked for semicolons and entries in the unparsed array are not sanitized, so attacker-influenced input can inject additional cookie attributes. For example, a domain value containing a semicolon can append attributes such as SameSite, and an unparsed entry can inject attributes such as HttpOnly, without the caller setting them. Applications that pass user-controlled input to these fields, such as multi-tenant or reverse-proxy servers that scope session cookies to a tenant-supplied domain, can have SameSite CSRF protections bypassed, or the Secure, HttpOnly, and SameSite attributes forced, stripped, or overridden. The issue is fixed in undici 6.28.0, 7.29.0, and 8.9.0.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | node-undici | no fix listed | DEBIAN-CVE-2026-16729 |
| Debian:13 | node-undici | no fix listed | DEBIAN-CVE-2026-16729 |
| Debian:14 | node-undici | 8.9.0+dfsg+~cs3.2.0-1 | DEBIAN-CVE-2026-16729 |
| Ubuntu:24.04:LTS | node-undici | no fix listed | UBUNTU-CVE-2026-16729 |
| Ubuntu:26.04:LTS | node-undici | no fix listed | UBUNTU-CVE-2026-16729 |
| Ubuntu:26.10 | node-undici | no fix listed | UBUNTU-CVE-2026-16729 |
| npm | undici | 8.9.0 | GHSA-v3r7-h72x-cjcm |
| npm | undici | 7.29.0 | GHSA-v3r7-h72x-cjcm |
| npm | undici | 6.28.0 | GHSA-v3r7-h72x-cjcm |
Affected products (as reported)
Weakness: CWE-74 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N