CVE-2025-58084 Overview
CVE-2025-58084 affects Mattermost Desktop App versions 5.13.0 and earlier. The application fails to validate URLs pointing to destinations external to configured Mattermost servers. An attacker on a server the user has joined can send a malformed URL that crashes the desktop client when processed. The flaw maps to CWE-1287: Improper Validation of Specified Type of Input and results in a denial of service against the client application. Exploitation requires user interaction with the malicious URL and does not expose confidentiality or integrity of user data.
Critical Impact
A remote attacker with access to a shared Mattermost server can crash any connected desktop client by delivering a crafted URL through normal messaging channels.
Affected Products
- Mattermost Desktop App versions <= 5.13.0
- Windows, macOS, and Linux desktop builds derived from the affected codebase
- Deployments where users connect to multiple or untrusted Mattermost servers
Discovery Timeline
- 2025-10-13 - CVE-2025-58084 published to the National Vulnerability Database
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-58084
Vulnerability Analysis
The Mattermost Desktop App embeds URL handling logic that processes links shared within channels and direct messages. The client trusts URLs originating from configured servers and does not enforce strict parsing on external URL references. When the parser receives a malformed URL structure, the application enters an unrecoverable state and terminates. The result is a client-side denial of service that disrupts availability for the targeted user.
The attack requires the victim to have joined a server controlled by, or accessible to, the attacker. Once the malicious URL is delivered, rendering or interacting with the message triggers the crash. Because the desktop client is the affected component, server-side content moderation does not mitigate the issue by default.
Root Cause
The root cause is improper validation of URL input external to the configured Mattermost server list. The URL handler accepts input that violates expected structural constraints and does not fail safely. Instead of rejecting the malformed input or catching the parsing exception, the client propagates the error into the main process and terminates.
Attack Vector
The vector is network-based and requires user interaction. An attacker with an account on a server the victim has configured posts or sends a message containing the crafted URL. When the client processes the message, the malformed URL triggers the crash. Repeated delivery allows persistent denial of service against the target account each time it reconnects.
No verified proof-of-concept code is publicly available. Refer to the Mattermost Security Updates advisory for vendor-supplied technical detail.
Detection Methods for CVE-2025-58084
Indicators of Compromise
- Repeated unexpected terminations of the Mattermost Desktop App process on user endpoints
- Crash reports or minidumps referencing URL parsing routines in the Mattermost client binary
- Inbound messages containing malformed URL schemes or oversized URL payloads from unfamiliar server peers
Detection Strategies
- Monitor endpoint telemetry for abnormal exit codes and repeated relaunches of the Mattermost Desktop process
- Correlate client crash events with recent message activity from specific senders or servers to identify targeted delivery
- Inspect Mattermost server audit logs for outbound messages containing anomalous URL structures
Monitoring Recommendations
- Enable application crash reporting and centralize collection for security review
- Track Mattermost Desktop client versions across the environment to identify hosts still running <= 5.13.0
- Alert on users repeatedly reconnecting after client termination within short time windows
How to Mitigate CVE-2025-58084
Immediate Actions Required
- Upgrade the Mattermost Desktop App to a version released after 5.13.0 that addresses CVE-2025-58084
- Inventory all endpoints running the desktop client and prioritize hosts that connect to third-party or community-operated servers
- Advise users to avoid interacting with unexpected URLs from untrusted server peers until patching is complete
Patch Information
Mattermost has published fixed builds through its security update channel. Consult the Mattermost Security Updates page for the specific fixed version and release notes covering CVE-2025-58084. Apply the patched client across all supported operating systems and verify the version string after upgrade.
Workarounds
- Restrict user configurations to trusted internal Mattermost servers only, reducing exposure to attacker-controlled peers
- Use the Mattermost web client in a hardened browser as a temporary alternative where feasible
- Enforce endpoint management policies that block installation of desktop client versions <= 5.13.0
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
