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Low severity3.7NVD Advisory· Published Jun 17, 2026· Updated Jun 25, 2026

CVE-2026-11525

CVE-2026-11525

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.

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Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
undicinpm
< 6.27.06.27.0
undicinpm
>= 7.0.0, < 7.28.07.28.0
undicinpm
>= 8.0.0, < 8.5.08.5.0

Affected products

57

Patches

Vulnerability mechanics

References

4

News mentions

0

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