Laravel Passport Authentication Bypass Vulnerability (CVE-2026-39976)

hello@craftedsignal.io — Thu, 09 Apr 2026 17:16:31 +0000

Laravel Passport, an OAuth2 server implementation for Laravel, is vulnerable to an authentication bypass (CVE-2026-39976) in versions 13.0.0 up to, but not including, 13.7.1. The vulnerability stems from the league/oauth2-server library, where the JWT sub claim is set to the client identifier for client_credentials tokens, as there is no associated user. Subsequently, the token guard uses this client identifier to retrieve user information via retrieveById() without proper validation, potentially resolving and authenticating an unrelated, real user. This means any machine-to-machine token can inadvertently authenticate as an actual user within the Laravel application. The vulnerability is resolved in Laravel Passport version 13.7.1. This allows attackers to perform actions with the privileges of the authenticated user.

Attack Chain

Attacker obtains a valid client_credentials token issued by Laravel Passport (versions 13.0.0 - 13.7.0). This could be a token intended for machine-to-machine communication.
The attacker sends a request to a protected endpoint of the Laravel application, including the client_credentials token in the Authorization header.
The Laravel Passport token guard extracts the JWT sub claim from the token. In vulnerable versions, this sub claim contains the client identifier.
The token guard calls retrieveById() using the client identifier from the sub claim as the user ID.
Due to the lack of validation, retrieveById() queries the user database, potentially finding a user whose ID matches the client identifier.
If a user with the matching ID is found, the application authenticates the request as that user, granting the attacker their privileges.
The attacker can then access resources and perform actions as the authenticated user.
The attacker exploits the user’s privileges to compromise data or perform unauthorized actions within the application.

Impact

Successful exploitation of CVE-2026-39976 allows attackers to bypass authentication and gain unauthorized access to user accounts in Laravel applications using affected versions of Laravel Passport. This can lead to data breaches, privilege escalation, and other malicious activities, depending on the privileges of the compromised user accounts. The severity of the impact depends on the application’s functionality and the sensitivity of the data it handles. Potentially all applications using Laravel Passport for authentication are vulnerable.

Recommendation

Upgrade Laravel Passport to version 13.7.1 or later to patch CVE-2026-39976.
Implement additional validation within the application’s authentication logic to verify that the user ID extracted from the JWT sub claim corresponds to a valid user, especially when using client_credentials tokens.
Monitor application logs for unexpected authentication events or API requests originating from machine-to-machine tokens that are being authenticated as users. The webserver log source can be used for this monitoring.
Deploy the Sigma rule provided to detect requests to protected endpoints with client_credentials tokens that are incorrectly authenticated as users.

XenForo OAuth2 Unauthorized Scope Request Vulnerability

hello@craftedsignal.io — Wed, 01 Apr 2026 01:16:40 +0000

XenForo, a popular forum software, has a security vulnerability (CVE-2025-71278) affecting versions prior to 2.3.5. Specifically, the vulnerability lies in the OAuth2 client application authorization process. OAuth2 clients can request scopes beyond those they are authorized to access. This vulnerability impacts any XenForo 2.3 installation utilizing OAuth2 clients prior to upgrading to version 2.3.5. Successful exploitation could allow malicious or compromised OAuth2 client applications to escalate privileges and access sensitive data or functionality within the XenForo forum.

Attack Chain

Attacker registers a malicious OAuth2 client application within the vulnerable XenForo instance.
The attacker crafts an OAuth2 authorization request, including scopes that the client should not be permitted to access according to XenForo’s intended authorization model.
The vulnerable XenForo instance fails to properly validate the requested scopes against the client’s authorized permissions.
The XenForo server grants access tokens with the requested, unauthorized scopes.
The malicious OAuth2 client application uses the access token with the expanded privileges to interact with the XenForo API.
The attacker performs actions they are not intended to be authorized for, such as accessing private user data, modifying forum settings, or performing administrative tasks depending on the scopes gained.

Impact

Successful exploitation of CVE-2025-71278 can lead to unauthorized data access, privilege escalation, and potential compromise of the XenForo forum. This can impact all users of the forum, leading to data breaches, defacement, or disruption of service. The severity depends on the unauthorized scopes obtained, but could range from accessing private messages to complete administrative control over the forum.

Recommendation

Upgrade XenForo installations to version 2.3.5 or later to remediate CVE-2025-71278 (reference: XenForo advisory in references).
Implement rate limiting on OAuth2 authorization requests to identify and mitigate potential abuse (reference: generic security best practice).

Oauth2 — CraftedSignal Threat Feed

Laravel Passport Authentication Bypass Vulnerability (CVE-2026-39976)

Attack Chain

Impact

Recommendation

XenForo OAuth2 Unauthorized Scope Request Vulnerability

Attack Chain

Impact

Recommendation