CVE-2017-18883

Vulnerability

Overview

When Mattermost Server is configured as an OAuth 2.0 Service Provider, the authorization data generated for OAuth flows has low entropy. This means the tokens or authorization codes are not sufficiently random, making them predictable to an attacker. The issue affects Mattermost Server versions prior to 4.3.0, 4.2.1, and 4.1.2 [1].

Exploitation and

Attack Surface

The vulnerability is present in the OAuth 2.0 provider functionality of Mattermost. An attacker who can obtain or predict the low-entropy authorization data could gain unauthorized access. No authentication is required to initiate an OAuth flow, but the attacker must be able to interact with the Mattermost OAuth endpoints. The low entropy reduces the difficulty of brute-force or prediction attacks on authorization codes or tokens [1].

Impact

Successful exploitation could allow an attacker to impersonate a legitimate user or application in the OAuth flow, potentially gaining access to resources that should be protected. The exact impact depends on the OAuth scope and permissions granted, but it could lead to unauthorized data access or privilege escalation within the Mattermost system [1].

Mitigation

The vulnerability is fixed in Mattermost Server versions 4.3.0, 4.2.1, and 4.1.2. Users should upgrade to one of these releases or later to ensure adequate entropy in OAuth authorization data. The Mattermost project provides security updates and encourages users to subscribe to security bulletins for timely notifications [2][3].