CVE-2026-75025 in Desktop App
Summary
by MITRE • 09/16/2026
Mattermost Desktop App versions <=6.2 6.2.2.0 Fixed an issue where Mattermost Desktop did not sufficiently restrict server-rendered content from accessing local or private network resources. Thanks to game0v3r for contributing to this improvement under the Mattermost responsible disclosure policy. Mattermost Advisory ID: MMSA-2026-00698
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Analysis
by VulDB Data Team • 09/16/2026
The vulnerability identified in Mattermost Desktop App versions 6.2 and earlier, specifically up to version 6.2.2.0, represents a critical security flaw related to the improper handling of server-rendered content within the application's user interface layer. This issue stems from insufficient restrictions placed on web views or embedded browsers that render HTML content fetched from Mattermost servers. In modern desktop applications built using frameworks like Electron, there is often an inherent risk if the environment allows rendered web pages to interact with local file systems or internal network services without adequate sandboxing. The flaw essentially permitted maliciously crafted server-side responses to execute code or perform actions that bypassed standard security boundaries, thereby granting unauthorized access to resources that should have remained isolated from the application's rendering engine.
From a technical perspective, this vulnerability aligns closely with CWE-79, which describes Cross-Site Scripting (XSS), and more specifically relates to issues where XSS leads to Local File Access or Server-Side Request Forgery due to improper configuration of web view security settings. When the application failed to sufficiently restrict server-rendered content, it allowed potential attackers who could inject malicious scripts into channels, direct messages, or other user-controllable fields within Mattermost to exploit these permissions. By leveraging this weakness, an attacker could potentially read local files on the victim's machine if appropriate file system APIs were exposed through the web view context. Furthermore, the vulnerability enabled access to private network resources, meaning that internal services such as database interfaces, administrative panels, or other intranet applications running on localhost or within the corporate LAN became reachable from the compromised application environment.
The operational impact of this flaw is significant for organizations relying on Mattermost Desktop for secure communication. An adversary with the ability to trick a user into viewing malicious content could exfiltrate sensitive data stored locally on the endpoint, such as configuration files, cached credentials, or proprietary documents. Additionally, by accessing private network resources, the attacker could pivot further into the internal network infrastructure. This capability transforms what might otherwise be an isolated client-side issue into a potential gateway for lateral movement and deeper penetration of corporate networks. The risk is exacerbated in enterprise environments where sensitive data resides on local drives or where critical services are hosted internally without additional perimeter defenses against requests originating from trusted desktop applications.
This incident was responsibly disclosed by the security researcher known as game0v3r under Mattermost's responsible disclosure policy, highlighting the importance of coordinated vulnerability management practices. The remediation involved updating the application to version 6.2.2.0 or later, where strict sandboxing and context isolation were implemented to prevent server-rendered content from accessing local file systems or internal network endpoints. To mitigate similar risks in existing deployments prior to upgrading, administrators should enforce Content Security Policy (CSP) headers strictly on their Mattermost servers to limit script execution sources and disable unnecessary features within the desktop app that expose web view APIs. Organizations are advised to immediately patch all instances of Mattermost Desktop to version 6.2.2.0 or higher to close this attack vector. Continuous monitoring for unusual network traffic originating from client endpoints can also help detect potential exploitation attempts in environments where immediate patching is not feasible.