CVE-2026-67336

critical · 9.4

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.

9.4

CVSS

0.2%

EPSS (exploit prob.)

5th

EPSS percentile

2026-08-01

Published

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Weaknesses

CWE-327

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

Query this programmatically:

curl https://evil-db.io/api/v1/cve/CVE-2026-67336