CVE-2026-67336
Received Received - Intake

Insecure Cryptographic Defaults in Better-Auth OIDC and MCP Plugins

Publication date: 2026-08-01

Last updated on: 2026-08-01

Assigner: VulnCheck

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.

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Meta Information

Published
2026-08-01
Last Modified
2026-08-01
Generated
2026-08-01
AI Q&A
2026-08-01
EPSS Evaluated
N/A
NVD
CVE-2026-67336
EUVD
EUVD-2026-51816

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
better-auth better-auth to 1.6.11 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-327 The product uses a broken or risky cryptographic algorithm or protocol.

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Executive Summary

better-auth versions before 1.6.11 have insecure cryptographic defaults in the oidcProvider and mcp plugins. These plugins 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.

Detection Guidance

Check if your better-auth version is below 1.6.11. Inspect OIDC provider and MCP plugin configurations for advertised none algorithm support and plain PKCE acceptance. Review token validation logic for unsigned token handling.

Impact Analysis

Attackers could gain unauthorized access to user accounts by exploiting unsigned tokens or intercepting authorization codes. This could lead to data breaches, unauthorized actions, or impersonation of users.

Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating GDPR's data protection requirements and HIPAA's security rules. Non-compliance may result in legal penalties, fines, or reputational damage.

Mitigation Strategies

Upgrade better-auth to version 1.6.11 or later. Disable the none algorithm in OIDC provider and MCP plugins. Enforce S256 PKCE method for authorization codes. Validate all tokens strictly for proper signatures.

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