CVE-2026-67336

High

Description

better-auth versions before 1.6.11 contain insecure cryptographic defaults in the oidcProvider and mcp plugins that advertise the none algorithm and accept plain PKCE by default. Attackers can exploit algorithm negotiation to accept unsigned tokens or intercept authorization codes when PKCE plain is used instead of the required S256 method.

SeverityHigh

CVSS8.7

Exploit probability—

ProductBetter-auth

PublishedAug 1, 2026

First seenAug 1, 2026

Weakness typeCWE-327CWE-327

How to fix

Update

better-auth1.6.11 or later

Vendor advisories

github.com/better-auth/better-auth/security/advisories/GHSA-9h47-pqcx-hjr4

Affected products

Product	Affected versions	Fixed in
better-authnpm	v < 1.6.11	1.6.11

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