CVE-2021-39138

Parse Server is an open source backend that can be deployed to any infrastructure that can run Node.js. Developers can use the REST API to signup users and also allow users to login anonymously. Prior to version 4.5.1, when an anonymous user is first signed up using REST, the server creates session incorrectly. Particularly, the authProvider field in _Session class under createdWith shows the user logged in creating a password. If a developer later depends on the createdWith field to provide a different level of access between a password user and anonymous user, the server incorrectly classified the session type as being created with a password. The server does not currently use createdWith to make decisions about internal functions, so if a developer is not using createdWith directly, they are not affected. The vulnerability only affects users who depend on createdWith by using it directly. The issue is patched in Parse Server version 4.5.1. As a workaround, do not use the createdWith Session field to make decisions if one allows anonymous login.

Weakness

The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. This allows attackers to bypass intended access restrictions.

Affected Software

Extended Description

Assuming a user with a given identity, authorization is the process of determining whether that user can access a given resource, based on the user’s privileges and any permissions or other access-control specifications that apply to the resource. When access control checks are incorrectly applied, users are able to access data or perform actions that they should not be allowed to perform. This can lead to a wide range of problems, including information exposures, denial of service, and arbitrary code execution.

Potential Mitigations

• Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) [REF-229] to enforce the roles at the appropriate boundaries.
• Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
• Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
• For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
• For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page.
• One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.

References

• https://github.com/parse-community/parse-server/commit/147bd9a3dc43391e92c36e05d5db860b04ca27db
• https://github.com/parse-community/parse-server/releases/tag/4.5.1
• https://github.com/parse-community/parse-server/security/advisories/GHSA-23r4-5mxp-c7g5