CVE-2024-39613: Mattermost Desktop App RCE Vulnerability

CVE-2024-39613 Overview

CVE-2024-39613 affects Mattermost Desktop App versions <=5.8.0 on Windows. The application fails to specify an absolute path when searching for the cmd.exe executable. A local attacker who places a malicious cmd.exe binary in the user's Downloads folder can trigger execution of that file when the application invokes the command shell. Successful exploitation results in local code execution under the context of the logged-in user. The weakness is categorized as [CWE-427] Uncontrolled Search Path Element.

Critical Impact
A malicious cmd.exe planted in the Downloads folder executes with the privileges of the Mattermost Desktop user, delivering full confidentiality, integrity, and availability impact.

Affected Products

Mattermost Desktop App versions <=5.8.0
Windows installations of the Mattermost Desktop client
Deployments where users have write access to the Downloads folder

Discovery Timeline

2024-09-16 - CVE-2024-39613 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2024-39613

Vulnerability Analysis

The flaw stems from an uncontrolled search path element in the Mattermost Desktop App. When the application spawns a child process using cmd.exe, it references the executable by name rather than by an absolute path. Windows resolves the binary using the standard search order, which includes the current working directory before system directories in certain contexts.

If the application's working directory is the user's Downloads folder, a planted cmd.exe in that folder is resolved and executed before the legitimate C:\Windows\System32\cmd.exe. Exploitation requires local access and user interaction, but no prior privileges are needed to stage the malicious file.

Root Cause

The root cause is failure to fully qualify the path to system utilities when creating child processes. Invoking cmd.exe without specifying C:\Windows\System32\cmd.exe allows Windows path resolution to prefer attacker-controlled locations under specific working-directory conditions.

Attack Vector

An attacker with local access, or one who tricks a user into saving a file named cmd.exe into the Downloads folder, primes the exploit. When the Mattermost Desktop App later invokes the shell while operating in that directory, the malicious binary runs. The attack chain relies on a benign-looking download combined with the application's insecure process invocation.

The vulnerability mechanism is documented in the Mattermost Security Updates advisory. No public proof-of-concept code is available at this time.

Detection Methods for CVE-2024-39613

Indicators of Compromise

Presence of an unexpected cmd.exe file inside a user's Downloads folder or other non-system directories
Process creation events where cmd.exe is launched from a path other than C:\Windows\System32\ or C:\Windows\SysWOW64\
Mattermost Desktop process (Mattermost.exe) spawning cmd.exe from a user-writable directory

Detection Strategies

Hunt for process-creation telemetry where the parent process is Mattermost.exe and the child image path for cmd.exe does not resolve to a system directory
Alert on file-write events that create binaries named cmd.exe in non-standard locations such as %USERPROFILE%\Downloads
Correlate download activity in browsers with subsequent execution of executables sharing names of Windows system utilities

Monitoring Recommendations

Enable Windows command-line and process-creation auditing (Event ID 4688) with full command-line logging
Ingest endpoint process telemetry into a centralized data lake to enable retroactive hunting for planted binaries
Baseline expected child processes of Mattermost Desktop to detect deviations from normal behavior

How to Mitigate CVE-2024-39613

Immediate Actions Required

Upgrade Mattermost Desktop App to a version later than 5.8.0 as published in the Mattermost Security Updates
Inventory endpoints running vulnerable Mattermost Desktop versions and prioritize patching
Inspect user Downloads folders for existing cmd.exe files and remove any unauthorized copies

Patch Information

Mattermost has issued fixed builds addressed through their security advisory channel. Refer to the Mattermost Security Updates page for the specific patched release and upgrade guidance.

Workarounds

Restrict user write access to directories where the Mattermost Desktop App may set its working directory
Apply application allowlisting to block execution of binaries from user-writable locations such as %USERPROFILE%\Downloads
Educate users to avoid downloading or saving files named after Windows system utilities like cmd.exe

bash

# Example: WDAC/AppLocker-style rule concept to deny execution of cmd.exe outside System32
# Deny: %USERPROFILE%\Downloads\cmd.exe
# Allow: C:\Windows\System32\cmd.exe