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CVE-2026-67336 high CVSS 8.7

Vulnerability in better-auth (CVE-2026-67336)

Summary

Vulnerability in better-auth (CVE-2026-67336). Confidential information can be exposed externally. Exploitable via Referer header. Mitigation: upgrade to 1.6.11 or later.

Original description

The description as published by the source.

Am I affected?

Users are affected if all of the following are true:

  • Their application uses better-auth at a version below the patched release.
  • Their application enables oidcProvider() from better-auth/plugins/oidc-provider or mcp() from better-auth/plugins/mcp (the mcp plugin delegates to oidcProvider and inherits both defaults).
  • For the algorithm-negotiation impact: relying parties of the application's OIDC server use a JWT verification library that performs algorithm negotiation from the discovery document without pinning to a specific signing algorithm.
  • For the PKCE impact: the authorization URL is exposed to any party other than the user agent and the application's OP.

If the application only uses @better-auth/oauth-provider (the canonical replacement) and have not enabled the legacy plugins, it is not affected. The new package's discovery document excludes none and its authorize schema rejects plain at parse time.

Fix:

  1. Upgrade to better-auth@1.6.11 or later.
  2. Migrate from the deprecated oidcProvider and mcp plugins to @better-auth/oauth-provider when feasible.
  3. If developers cannot upgrade their applications, see workarounds below.

Summary

The legacy oidcProvider and mcp plugins exhibit two related defects in their OIDC discovery and authorize surfaces.

The discovery document advertises "none" in id_token_signing_alg_values_supported (and, for mcp, in resource_signing_alg_values_supported on the OAuth p…

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-67336 has been found in better-auth.
Attackers can target a specific entry point like Referer header over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 8.7/10.
What to do: upgrade better-auth to 1.6.11 or later.
If unsure, ask your IT team or search "better-auth CVE-2026-67336" on the vendor's site.

CVE-2026-67336 (better-auth) — CWE-1188 / CVSS v3 8.7
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: Referer header / oidcProvider / none / plain
Patched: 1.6.11 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-1188) exists in better-auth. Attackers reach the vulnerable code path via Referer header without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of better-auth. Attack surface: Referer header / oidcProvider / none / plain.

🔥 Severity

Severity: High (CVSS 8.7/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 1.6.11.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'better-auth' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'better-auth' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で better-auth を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade better-auth to 1.6.11

    ステージング環境で 1.6.11 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

npm better-auth
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"1.6.11"}]}]

References

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