CVE-2026-67336

Severity CVSS v4.0:

CRITICAL

Type:

CWE-327 Use of a Broken or Risky Cryptographic Algorithm

Publication date:

01/08/2026

Last modified:

03/08/2026

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.

Impact

Vector 4.0

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 CVSS v4.0 Severity and Metrics:

Base Score: 9.40 CRITICAL
Vector: 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

Attack Vector (AV): Network
Attack Complexity (AC): High
Attack Requirements (AT): Present
Privileges Required (PR): None
User Interaction (UI): None
Confidentiality (VC): High
Integrity (VI): High
Availability (VA): None
Confidentiality (SC): High
Integrity (SI): High
Availability (SA): None

Base Score 4.0

9.40

Severity 4.0

CRITICAL

Vector 3.x

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N CVSS v3.1 Severity and Metrics:

Base Score: 8.70 HIGH
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N

Attack Vector (AV): Network
Attack Complexity (AC): High
Privileges Required (PR): None
User Interaction (UI): None
Scope (S): Changed
Confidentiality (C): High
Integrity (I): High
Availability (A): None

Base Score 3.x

8.70

Severity 3.x

HIGH

CVE-2026-67336

Description

Impact

References to Advisories, Solutions, and Tools