# CVE-2026-11525

## Summary

- **CVE ID:** CVE-2026-11525
- **Severity:** LOW
- **CVSS Score:** 3.7 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N)
- **CWE:** CWE-183
- **Published:** Jun 17, 2026
- **Last Modified:** Jun 20, 2026

## 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.

## Affected Products

- undici — undici (0)
- undici — undici (6.26.0)
- undici — undici (7.0.0)
- undici — undici (7.28.0)
- undici — undici (8.0.0)
- undici — undici (8.5.0)

## References

- [CNA](https://github.com/nodejs/undici/security/advisories/GHSA-g8m3-5g58-fq7m)
- [CNA](https://cna.openjsf.org/security-advisories.html)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.24%
- **EPSS Percentile:** 14.9

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._