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CVE-2026-67333 high CVSS 7.2

Open Redirect in better-auth (CVE-2026-67333)

Summary

Vulnerability in better-auth (CVE-2026-67333). Confidential information can be exposed externally. Exploitable via POST /oauth2/register. Mitigation: upgrade to 1.7.0-beta.4 or later.

Original description

The description as published by the source.

Am I affected?

Check each condition. Users are affected when all of the first three hold.

  • Their application enables the oidc-provider plugin or the mcp plugin from better-auth/plugins. The mcp plugin wraps the same provider and carries the same defect. Both are on the migration path to @better-auth/oauth-provider, which is not affected.
  • Their application better-auth version is 1.6.12 or earlier on the stable line, or any 1.7.0-beta build on the pre-release line. Both release lines carry the same defect.
  • Their application consent page is a client component that reads redirectURI from the authClient.oauth2.consent(...) response and assigns it to a browser navigation target such as window.location.href, location.assign, or location.replace.

Two conditions raise an application's exposure:

  • It sets allowDynamicClientRegistration: true. Client registration is then unauthenticated, so any visitor can plant the malicious client. The default is false, which limits planting to authenticated users.
  • It exposes the consent page to ordinary end users rather than to a restricted operator audience.

A developer's application is not affected when any of these hold:

  • Their application copied the project's consent-buttons.tsx demo verbatim. That file reads a uri field that this plugin never returns, so its navigation branch never runs and it falls through to an error toast.
  • Their application completse the consent flow with a server-side red…

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-2026-67333 has been found in better-auth.
Attackers can target a specific entry point like POST /oauth2/register over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 7.2/10.
What to do: upgrade better-auth to 1.7.0-beta.4 or later.
If unsure, ask your IT team or search "better-auth CVE-2026-67333" on the vendor's site.

CVE-2026-67333 (better-auth) — CWE-601 / CVSS v3 7.2
Attack vector: remote (network-reachable)
Attack surface: POST /oauth2/register / GET /oauth2/authorize / mcp / redirectURI
Patched: 1.7.0-beta.4 — 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-601) exists in better-auth. Attackers reach the vulnerable code path via POST /oauth2/register.

📍 Affected scope

Check the vendor advisory for the affected versions of better-auth. Attack surface: POST /oauth2/register / GET /oauth2/authorize / mcp / redirectURI.

🔥 Severity

Severity: High (CVSS 7.2/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 1.7.0-beta.4.

🛡️ 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 POST /oauth2/register requests with malformed payloads or SQL meta-characters. 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
    Hunt for indicators of compromise detect 
    grep 'POST /oauth2/register' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'

    アクセスログで POST /oauth2/register への異常なリクエスト (不正な認証ヘッダ・SQLメタ文字)を過去 30〜90日分捜索。WAF/SIEM があれば該当パスのアラート発火履歴を確認。

  3. 3
    Apply patch patch 
    Upgrade better-auth to 1.7.0-beta.4

    ステージング環境で 1.7.0-beta.4 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と、Step 2 で見つけた異常検知の続報チェックを含めること。

  4. 4
    Post-deployment verification verify 
    Replay attack against POST /oauth2/register on staging to confirm patch closes the vector

    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 Step 2 と同じログクエリでアラート再発が無いか継続監視。

Affected packages

npm better-auth
[{"type":"SEMVER","events":[{"introduced":"1.7.0-beta.0"},{"fixed":"1.7.0-beta.4"}]}]

References

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