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.
How to fix
- nodejs undici6.27.0, 7.28.0, 8.5.0 or later
- undici6.27.0, 7.28.0, 8.5.0 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| nodejs undici | v < 6.27.0, 7.0.0 ≤ v < 7.28.0, 8.0.0 ≤ v < 8.5.0 | 6.27.0, 7.28.0, 8.5.0 |
| undicinpm | v < 6.27.0, 7.0.0 ≤ v < 7.28.0, 8.0.0 ≤ v < 8.5.0 | 6.27.0, 7.28.0, 8.5.0 |
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