CVE-2026-11525
Published:June 17, 2026
Updated:June 21, 2026
Impact:
When undici parses a Set-Cookie header, it accepts any SameSite attribute value that contains Strict, Lax, or None as a substring, rather than the case-insensitive exact match specified by RFC 6265. Non-spec values are silently mapped to one of the three standard tokens. For example, SameSite=NoneOfYourBusiness is parsed as None (the most permissive setting), and SameSite=StrictLax is parsed as Lax (a downgrade from Strict).
Affected applications are those that consume Set-Cookie headers from server responses (for example via undici's fetch or proxy code paths) and then forward or rely on the parsed sameSite attribute. A malicious or non-compliant server can coerce the consumer's view of a cookie's SameSite policy to a weaker value, silently degrading the SameSite enforcement the cookie is supposed to provide.
This was introduced in undici 5.15.0 when the cookies feature was added.
Patches:
Upgrade to undici v6.26.0, v7.28.0 or v8.5.0.
Workarounds:
After parsing a Set-Cookie header, validate that the resulting sameSite attribute is one of 'Strict', 'Lax', or 'None' (exact, case-insensitive) before forwarding or relying on it.
Affected Packages
https://github.com/nodejs/undici.git (GITHUB):
Affected version(s) >=v7.0.0 <v7.28.0Fix Suggestion:
Update to version v7.28.0https://github.com/nodejs/undici.git (GITHUB):
Affected version(s) >=v8.0.0 <v8.5.0Fix Suggestion:
Update to version v8.5.0https://github.com/nodejs/undici.git (GITHUB):
Affected version(s) >=v6.0.0 <v6.27.0Fix Suggestion:
Update to version v6.27.0undici (NPM):
Affected version(s) >=8.0.0 <8.5.0Fix Suggestion:
Update to version 8.5.0undici (NPM):
Affected version(s) >=7.0.0 <7.28.0Fix Suggestion:
Update to version 7.28.0undici (NPM):
Affected version(s) >=0.1.0 <6.27.0Fix Suggestion:
Update to version 6.27.0undici (NPM):
Affected version(s) >=6.0.0 <6.27.0Fix Suggestion:
Update to version 6.27.0Related Resources (4)
Do you need more information?
Contact UsCVSS v4
Base Score:
6.3
Attack Vector
NETWORK
Attack Complexity
HIGH
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
LOW
Vulnerable System Availability
NONE
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
3.7
Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
LOW
Availability
NONE
Weakness Type (CWE)
Permissive List of Allowed Inputs
EPSS
Base Score:
0.20