CVE-2026-67336: better-auth before 1.6.11 Insecure Cryptographic Defaults via oidcProvider

Severity: high (CVSS 8.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-01 · updated 2026-09-08
Weakness: CWE-327

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.

Affected products

better-auth: before 1.6.11 — fixed in 1.6.11

How to fix

Upgrade to a fixed version: better-auth 1.6.11. Check the vendor advisory for mitigations.

References

https://github.com/better-auth/better-auth/security/advisories/GHSA-9h47-pqcx-hjr4
https://www.vulncheck.com/advisories/better-auth-before-insecure-cryptographic-defaults-via-oidcprovider

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