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GHSA-v3r7-h72x-cjcm CVE-2026-16729

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

Medium npm
Severity
4.8 / 10
Medium · CVSS 3.1
Exploit chance (EPSS)
0.28%
Chance of exploitation in the next 30 days. Higher than 20.32% of scored vulnerabilities.
Known exploited
No
Not in CISA's catalog
Weakness
CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
Fix
6.28.0
Upgrade undici to this version or later

Description

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.

Affected versions

npm

PackageVulnerableFixed in
undici
< 6.28.0
6.28.0
undici
>= 7.0.0, < 7.29.0
7.29.0
undici
>= 8.0.0, < 8.9.0
8.9.0
undici
< 6.28.0
6.28.0
undici
>= 7.0.0, < 7.29.0
7.29.0
undici
>= 8.0.0, < 8.9.0
8.9.0

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

undici npm → 6.28.0

npm
npm install undici@6.28.0
yarn
yarn add undici@6.28.0
pnpm
pnpm add undici@6.28.0

Severity breakdown

CVSS 3.1 4.8

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

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

Weakness

CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')

The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component.

How to prevent it
  • Requirements: Programming languages and supporting technologies might be chosen which are not subject to these issues.
  • Implementation: Utilize an appropriate mix of allowlist and denylist parsing to filter control-plane syntax from all input.

References

Advisories

Fixes and patches

Packages

Other links

Timeline

  1. Published
  2. Last updated by the source
  3. Latest EPSS score
AdvisorySeverityWhy it's related
GHSA-55wc-3pg8-jfw6
undici vulnerable to Denial of Service via unhandled exception in the decompress interceptor
High Also affects undici
GHSA-qrxm-fqhp-jwvm
undici vulnerable to Denial of Service via TLS 1.2 certificate-changing renegotiation
High Also affects undici
GHSA-9fm3-97px-rjf6
undici WebSocket client vulnerable to Denial of Service via unbounded automatic PONG buffering
High Also affects undici
GHSA-4qv8-2p9j-2685
undici vulnerable to Denial of Service via unbounded memory in the EventSource parser
High Also affects undici
GHSA-xjj6-f33q-929c
undici vulnerable to Denial of Service via unhandled error on excessive content-encodings
High Also affects undici
GHSA-f72v-6w45-q472
undici vulnerable to Subresource Integrity bypass via non-lowercase algorithm tokens
High Also affects undici
GHSA-4w7w-5xrc-9h26
undici vulnerable to cache poisoning and cross-user disclosure via cross-origin redirects
Critical Also affects undici
GHSA-2m5v-pch6-74hx
undici vulnerable to TLS certificate validation bypass via dropped tls options in Agent
Critical Also affects undici

Credits: UlisesGascon, Zelys-DFKH, mcollina

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