Unexpected Input to Server Webhook endpoint Causes DoS in Mattermost Confluence Plugin

CVE-2025-53514 is a denial-of-service (DoS) vulnerability in the Mattermost Confluence Plugin, affecting versions earlier than 1.5.0. The plugin fails to properly validate or reject unexpected request bodies when handling incoming webhooks from Confluence [1]. This lack of input validation allows malformed payloads to trigger an unhandled error within the plugin's request processing code.

An attacker can exploit this flaw by repeatedly sending crafted, invalid HTTP request bodies to the Confluence plugin's webhook endpoint. No authentication or special network position is required if the webhook endpoint is publicly accessible [1]. Each malformed request forces the plugin to attempt parsing the unexpected data, leading to a crash. By continuously hitting the endpoint, the attacker can keep the plugin in a crashed state, effectively blocking legitimate Confluence notifications and integrations.

The impact is a reliable denial of service against the Confluence plugin, disrupting the flow of Confluence event notifications (e.g., page updates, comments) into Mattermost channels [2]. This can hinder team collaboration and automation workflows that depend on the integration. No data exfiltration or code execution is described in the available sources.

Mattermost patched the vulnerability in Confluence Plugin version 1.5.0 [1]. Users running earlier versions should upgrade to at least 1.5.0 to prevent the DoS attack. As of the publication date, no workarounds have been publicly documented; restricting network access to the webhook endpoint may be a partial mitigation until patching.