3.7
LOW CVSS 3.1
CVE-2026-11525
undici vulnerable to Set-Cookie SameSite attribute downgrade via permissive substring matching
Description

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.

INFO

Published Date :

June 17, 2026, 5:31 p.m.

Last Modified :

June 17, 2026, 5:31 p.m.

Remotely Exploit :

Yes !

Source :

openjs
Affected Products

The following products are affected by CVE-2026-11525 vulnerability. Even if cvefeed.io is aware of the exact versions of the products that are affected, the information is not represented in the table below.

No affected product recoded yet

CVSS Scores
The Common Vulnerability Scoring System is a standardized framework for assessing the severity of vulnerabilities in software and systems. We collect and displays CVSS scores from various sources for each CVE.
Score Version Severity Vector Exploitability Score Impact Score Source
CVSS 3.1 LOW ce714d77-add3-4f53-aff5-83d477b104bb
CVSS 3.1 LOW MITRE-CVE
Solution
Upgrade undici to a patched version or validate SameSite attribute values after parsing.
  • Upgrade undici to v6.26.0, v7.28.0, or v8.5.0.
  • Validate SameSite attribute values post-parsing.

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