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CVE-2026-67335 medium CVSS 5.3

Authentication Bypass in better-auth (CVE-2026-67335)

Summary

Authentication bypass in better-auth (CVE-2026-67335). Data can be tampered with by attackers. Exploitable via getToken. Mitigation: upgrade to 1.6.2 or later.

Original description

The description as published by the source.

Am I affected?

Users are affected if all of the following are true:

  • The application uses better-auth at a version below 1.6.2 (or @better-auth/sso paired with such a version).
  • betterAuth({ account: { storeStateStrategy } }) is set to "cookie". The default "database" is not affected.
  • The application wires at least one OAuth provider through genericOAuth({ config }) with pkce: false, or it supplies a custom getToken or tokenUrl that does not require the stored codeVerifier. Stock social providers with PKCE on are not affected.
  • The provider returns arbitrary code values to the configured callback URL.

If users are on better-auth@1.6.2 or later, they are not affected.

Fix:

  1. Upgrade to better-auth@1.6.2 or later (current stable is 1.6.10).
  2. If users cannot upgrade, see workarounds below.

Summary

In parseGenericState, the cookie branch decrypted the oauth_state cookie and validated expiry, but did not compare the incoming OAuth state query parameter to the nonce that generateGenericState issued at sign-in. Any callback to /api/auth/oauth2/callback/ that arrived with a forged state and any code was therefore accepted as long as the browser still held a live oauth_state cookie. With pkce: false (or any getToken path that does not enforce a code-verifier round-trip), an attacker who forced the victim to deliver an attacker-controlled authorization code to the callback would mint a session bound to the attacke…

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-2026-67335 has been found in better-auth.
Attackers can target a specific entry point like getToken over the network to misuse the product.
Data can be tampered with by attackers. CVSS score: 5.3/10.
What to do: upgrade better-auth to 1.6.2 or later.
If unsure, ask your IT team or search "better-auth CVE-2026-67335" on the vendor's site.

CVE-2026-67335 (better-auth) — CWE-287 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: getToken / tokenUrl / codeVerifier / code
Patched: 1.6.2 — 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

Authentication bypass (CWE-287) exists in better-auth. Attackers reach the vulnerable code path via getToken without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of better-auth. Attack surface: getToken / tokenUrl / codeVerifier / code.

🔥 Severity

Severity: Medium (CVSS 5.3/10). Data can be tampered with by attackers.

🔧 How to fix

Update to 1.6.2.

🛡️ 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 1.6.2

    ステージング環境で 1.6.2 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":"1.6.2"}]}]

References

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