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CVE-2025-71401 medium CVSS 5.9

Vulnerability in better-auth (CVE-2025-71401)

Summary

Vulnerability in better-auth (CVE-2025-71401). Risk of unauthorized operations or information disclosure. Exploitable via baseURL. Mitigation: upgrade to 1.4.2 or later.

Original description

The description as published by the source.

Summary

Affected versions of Better Auth allow an external request to configure baseURL when it isn’t defined through any other means. This can be abused to poison the router’s base path, causing all routes to return 404 for all users.

This issue is only exploitable when baseURL is not explicitly configured (e.g., BETTER_AUTH_URL is missing) and the attacker is able to make the very first request to the server after startup. In properly configured environments or typical managed hosting platforms, this fallback behavior cannot be reached.

Details

A combination of X-Forwarded-Host and X-Forwarded-Proto is implicitly trusted. This allows the first request to configure baseURL whenever it is not explicitly configured.

Here's the code that reads the headers:

Here's the call to getBaseURL(), the result is assigned to ctx.baseURL.

Here's the router receiving the poisoned basePath:

X-Forwarded-Host and X-Forwarded-Proto can be used to modify the pathname of a parsed URL object which forms baseURL. basePath is then derived from the pathname of baseURL. Once the router basePath is poisoned it fails to match & route incoming requests.

Repro

Start a better-auth server with no baseURL configuration.

Send the following request as the first request to the server:

curl -i --location 'https://example.com/api/auth/ok' \
--header 'X-Forwarded-Proto: some:' \
--header 'X-Forwarded-Host: junk'

The better-auth API check endpoint retur…

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-2025-71401 has been found in better-auth.
Attackers can target a specific entry point like baseURL over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.9/10.
What to do: upgrade better-auth to 1.4.2 or later.
If unsure, ask your IT team or search "better-auth CVE-2025-71401" on the vendor's site.

CVE-2025-71401 (better-auth) — CWE-770 / CVSS v3 5.9
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: baseURL / BETTER_AUTH_URL / ctx.baseURL / basePath
Patched: 1.4.2 — 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

A vulnerability (CWE-770) exists in better-auth. Attackers reach the vulnerable code path via baseURL without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of better-auth. Attack surface: baseURL / BETTER_AUTH_URL / ctx.baseURL / basePath.

🔥 Severity

Severity: Medium (CVSS 5.9/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 1.4.2.

🛡️ 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 1.4.2

    ステージング環境で 1.4.2 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":"1.4.2"}]}]

References

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