Unexpected input to Update Channel Subscription endpoint causes DoS in Mattermost Confluence Plugin

Overview

The Mattermost Confluence Plugin versions before 1.5.0 fails to properly validate the request body when processing updates to channel subscriptions. This vulnerability, identified as CVE-2025-52931, allows an unauthenticated attacker to repeatedly send malformed requests to the update channel subscription endpoint, causing the plugin to crash [1].

Exploitation

An attacker does not need prior authentication to exploit this flaw. By sending a continuous stream of requests with an unexpected or invalid body to the endpoint responsible for updating channel subscriptions, the plugin enters an unhandled state that leads to a crash. The attack can be performed remotely over the network, and the only requirement is network access to the Mattermost instance with the vulnerable plugin enabled [1].

Impact

Successful exploitation results in a denial of service (DoS) condition for the plugin, making it unavailable for legitimate users. This prevents Confluence notifications from being delivered to Mattermost channels, disrupting workflows that rely on real-time updates [1]. The plugin must be restarted to restore functionality.

Mitigation

The vulnerability is fixed in Mattermost Confluence Plugin version 1.5.0. Users should upgrade to this version or later to prevent the attack [1]. No workaround is described in the source material. The vulnerability is not currently listed on CISA's Known Exploited Vulnerabilities (KEV) catalog.