CVE-2026-12284 in Desktop App
Summary
by MITRE • 09/17/2026
Mattermost Desktop App versions <=6.2 6.2.2.0 fails to validate the IPC sender in the leaveCall handler which allows a malicious or compromised Mattermost server (or a user with script access to a connected server view) to disconnect an active call belonging to a different connected server via the desktopAPI.leaveCall IPC message. Mattermost Advisory ID: MMSA-2026-00699
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified in Mattermost Desktop App versions 6.2 and earlier, specifically up to version 6.2.2.0, represents a critical failure in inter-process communication security within the application's desktop client architecture. This flaw is rooted in an insufficient validation of the sender identity for IPC messages, particularly affecting the leaveCall handler function. In modern desktop applications built on frameworks like Electron or similar hybrid technologies, internal components communicate via Inter-Process Communication channels to coordinate actions between the main process and renderer processes. The security model relies heavily on strict origin checks and sender verification to ensure that only trusted sources can trigger sensitive operations such as terminating active communication sessions.
The technical core of this vulnerability lies in the absence of rigorous authentication or authorization checks when processing IPC messages directed at the leaveCall endpoint. When a user initiates an audio or video call, the application maintains state regarding which server and session are currently active. The desktop API exposes methods to manage these calls, including disconnecting them. However, because the sender validation is missing or flawed, any entity capable of injecting JavaScript into the renderer process can invoke this method without restriction. This architectural oversight effectively bypasses the intended isolation boundaries between different Mattermost servers that a user might be logged into simultaneously within the same desktop instance.
The operational impact of this flaw allows for significant disruption to ongoing communications. A malicious or compromised Mattermost server, or an attacker who has achieved script execution capabilities through cross-site scripting vulnerabilities on a connected server view, can exploit this weakness to forcibly disconnect active calls belonging to users associated with different servers within the same desktop environment. This means that if a user is logged into multiple workspaces and one of those workspaces is compromised, the attacker does not need direct access to the victim's other sessions to cause harm; they simply need to trigger an IPC message from their controlled context. The result is a denial of service for active voice or video conferences, potentially disrupting critical business communications, meetings, or collaborative efforts that rely on uninterrupted connectivity.
From a classification perspective, this vulnerability aligns with CWE-284 Improper Access Control and CWE-749 Exposed Dangerous Method in the Common Weakness Enumeration framework. The failure to validate the IPC sender constitutes an access control bypass where untrusted input is allowed to perform privileged operations. In terms of offensive security tactics, this behavior corresponds to MITRE ATT&CK technique T1053 Scheduled Task/Job or more specifically lateral movement and command execution via local system APIs, although in this context it manifests as unauthorized state manipulation within the application layer rather than OS-level control. The attack vector leverages the trust relationship between different renderer contexts that share the same underlying process space but are logically separated by server boundaries.
Mitigation strategies must focus on immediate patching and architectural hardening of IPC handlers. Users running Mattermost Desktop App versions 6.2 or earlier, including version 6.2.2.0, should upgrade to a patched release immediately where this validation logic has been corrected. For organizations deploying the application via enterprise management tools, ensuring that update policies enforce the latest secure version is essential. From a development standpoint, all IPC handlers must implement strict sender verification using origin checks or token-based authentication mechanisms provided by the underlying framework. Developers should also adopt a principle of least privilege for IPC messages, ensuring that only specific, whitelisted contexts can invoke sensitive functions like call termination. Additionally, implementing Content Security Policy directives to restrict script execution from untrusted origins on server views will reduce the attack surface available to potential exploiters seeking to inject malicious code into the renderer process.