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Vulnerability record · CVE-2026-67336 · published 1 August 2026

CVE-2026-67336: Broken cryptographic algorithm vulnerability

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 4.0 Critical EPSS 0.24% · top 86.8% CWE-327 · Broken cryptographic algorithm Deferred
9.4CVSS 4.0 base score
0.24%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
2References
8 Sep 2026Last modified by NVD

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.

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:

References

LinkTags
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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Source: NIST National Vulnerability Database (record CVE-2026-67336), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.