CVE-2017-18871

Vulnerability

Overview CVE-2017-18871 is a denial of service vulnerability affecting Mattermost Server versions before 4.5.0, 4.4.5, 4.3.4, and 4.2.2. The root cause is the improper handling of an @ character placed before a JavaScript field name, which leads to an application crash when processed.

Exploitation

An attacker can exploit this vulnerability by crafting a request that includes an @ character immediately before a JavaScript field name. The issue can be triggered without any special authentication or elevated privileges, as it typically involves sending a crafted message or API request that is parsed by the server. No user interaction is required beyond delivering the payload to the server.

Impact

Successful exploitation results in a denial of service by crashing the Mattermost Server, making the platform unavailable to all users. This can disrupt team communication and workflows until the server is restarted or patched. The vulnerability is rated with a CVSS v3 base score of 7.5 (High) under the NVD assessment, indicating high availability impact [1].

Mitigation

Mattermost released fixes in versions 4.5.0, 4.4.5, 4.3.4, and 4.2.2 [1]. Administrators should update to one of these patched versions or later. As of the publication date (2020-06-19), the vulnerability had not been listed in CISA's Known Exploited Vulnerabilities catalog, but immediate patching is recommended. The Mattermost security updates page [3] provides guidance for subscribing to future security bulletins.