# CVE-2026-67336: Better Auth insecure cryptographic defaults in oidcProvider

Source: https://junglewise.ai/threats/cve-2026-67336-better-auth-insecure-cryptographic-defaults-in-oidcprovider  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-01. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-67336 · Severity: high · CVSS 8.7 · Published 2026-08-01

Better Auth is an authentication library used to manage login and user identity in web applications. The legacy oidcProvider plugin advertises support for unsigned tokens and allows weak password-protection methods by default, which could allow attackers to forge tokens or intercept authorization codes if users connect through compromised networks or untrusted proxies. Organizations using the affected versions should upgrade immediately or apply workarounds to disable these dangerous defaults.

Technologies: [better-auth (npm)](https://junglewise.ai/threats/technologies/better-auth). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2026-67336 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-67336 being exploited in the wild.

**How severe is CVE-2026-67336?** High severity, with a CVSS score of 8.7, published 1 August 2026.

**Which products and versions are affected?** better-auth (npm) SEMVER:introduced=0,fixed=1.6.11.

**Is there a fix for CVE-2026-67336?** Yes. better-auth (npm): upgrade to 1.6.11 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-67336 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-67336?** Check whether you run better-auth (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- better-auth (npm): upgrade to 1.6.11 or later

  ```sh
  npm install better-auth@1.6.11
  ```


## Technical details

Better Auth's legacy oidcProvider and mcp plugins contain two cryptographic weaknesses: (1) the OIDC discovery document advertises "alg=none" in id_token_signing_alg_values_supported, allowing relying parties that perform algorithm negotiation without pinning to accept unsigned JWT tokens, and (2) plain PKCE (Proof Key for Authorization Code Exchange) is enabled by default instead of the required S256 method, leaving authorization codes unprotected if the authorization URL is exposed via referrer headers, browser history, or proxy logs. The vulnerable code path silently downgrades missing code_challenge_method parameters to "plain" before enforcement checks, contradicting the discovery document which claims only S256 is supported. This violates RFC 9700 (OAuth 2.1) which explicitly forbids plain PKCE. Attackers with network visibility can exploit the algorithm negotiation weakness to forge tokens, or exploit weak PKCE to intercept authorization codes. The replacement @better-auth/oauth-provider is unaffected; the fix (version 1.6.11+) removes "none" from metadata and defaults allowPlainCodeChallengeMethod to false.

## Affected products

- Better Auth better-auth < 1.6.11

## Identifiers

- CVE-2026-67336
- GHSA-9h47-pqcx-hjr4

## Timeline

- 2026-07-07: disclosed: GHSA-9h47-pqcx-hjr4 published; CVE-2026-67336 assigned
- 2026-05-31: patched: Fixed in better-auth 1.6.11

## References

- [https://github.com/better-auth/better-auth/security/advisories/GHSA-9h47-pqcx-hjr4](https://github.com/better-auth/better-auth/security/advisories/GHSA-9h47-pqcx-hjr4)
- [https://github.com/better-auth/better-auth](https://github.com/better-auth/better-auth)

## Related threats

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