CVE-2025-22859: Fortinet FortiClientEMS Path Traversal Flaw

CVE-2025-22859 Overview

CVE-2025-22859 is a Relative Path Traversal vulnerability [CWE-23] affecting Fortinet FortiClient Enterprise Management Server (EMS) versions 7.4.0 through 7.4.1 and FortiClientEMS Cloud versions 7.4.0 through 7.4.1. The flaw allows a remote unauthenticated attacker to perform limited arbitrary file writes on the system through crafted upload requests. Fortinet published the advisory FG-IR-24-552 on May 13, 2025, addressing the issue in updated releases. The vulnerability targets the file upload handler, where insufficient path sanitization enables directory traversal sequences to escape the intended upload directory.

Critical Impact
Unauthenticated remote attackers can write files to arbitrary locations on the FortiClientEMS host, potentially enabling file tampering, configuration modification, or supporting follow-on attacks against management infrastructure.

Affected Products

Fortinet FortiClientEMS versions 7.4.0 through 7.4.1
Fortinet FortiClientEMS Cloud versions 7.4.0 through 7.4.1
Managed endpoints and downstream systems dependent on the EMS host

Discovery Timeline

2025-05-13 - CVE-2025-22859 published to NVD alongside Fortinet advisory FG-IR-24-552
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-22859

Vulnerability Analysis

The vulnerability resides in the file upload handling logic of FortiClientEMS. The upload endpoint accepts a file path or filename parameter that is not properly normalized before being joined with a base directory. An attacker can supply relative path sequences such as ../ to redirect the write operation to a location outside the intended upload directory. Because the endpoint does not require authentication, any network-reachable attacker can invoke it. The impact is characterized as a limited arbitrary file write, meaning attackers can create or overwrite files but with constraints imposed by the upload workflow and target process privileges.

Root Cause

The root cause is improper limitation of a pathname to a restricted directory, mapped to [CWE-23]. FortiClientEMS constructs the destination file path by concatenating user-supplied input with a fixed base directory without canonicalizing the result or rejecting parent-directory traversal sequences. This class of flaw typically stems from missing input validation, absent path canonicalization, and reliance on client-side controls to constrain destination paths.

Attack Vector

Exploitation requires network access to the FortiClientEMS management interface and does not require credentials or user interaction. An attacker sends an HTTP upload request containing traversal sequences in the target path parameter. The server processes the request, resolves the manipulated path, and writes attacker-controlled content to the resulting location on disk. Depending on the writable location, this can be used to modify EMS resources, plant files in scheduled task or web-accessible directories, or corrupt integrity-sensitive files. See the Fortinet Security Advisory FG-IR-24-552 for vendor-confirmed details.

Detection Methods for CVE-2025-22859

Indicators of Compromise

HTTP upload requests to FortiClientEMS endpoints containing ../, ..\, or URL-encoded traversal sequences such as %2e%2e%2f
Unexpected new files appearing outside the standard FortiClientEMS upload directory
Modified timestamps on FortiClientEMS configuration, script, or web resource files without corresponding administrative activity
Requests from unauthenticated sources that succeed against upload endpoints normally restricted to managed clients

Detection Strategies

Inspect web server and application logs for upload requests containing traversal patterns or absolute path characters in filename parameters
Deploy file integrity monitoring on FortiClientEMS installation directories, web roots, and any location writable by the EMS service account
Correlate upload request source IPs against expected management network ranges and flag external or unauthenticated origins
Alert on anomalous file creation events by the FortiClientEMS process outside its normal working directories

Monitoring Recommendations

Enable verbose HTTP logging on the FortiClientEMS management interface and forward logs to a centralized analytics platform
Baseline normal upload volume and destination paths, then alert on deviations
Monitor for post-write execution attempts such as new scheduled tasks, service modifications, or child process creation by the EMS service

How to Mitigate CVE-2025-22859

Immediate Actions Required

Upgrade FortiClientEMS and FortiClientEMS Cloud to a fixed version as specified in Fortinet advisory FG-IR-24-552
Restrict network access to the FortiClientEMS management interface to trusted administrative networks only
Audit the EMS host for unexpected files or modifications introduced since the vulnerable versions were deployed
Review web server and application logs for prior exploitation attempts using traversal sequences

Patch Information

Fortinet released fixed builds for FortiClientEMS 7.4.x and FortiClientEMS Cloud 7.4.x. Consult the Fortinet Security Advisory FG-IR-24-552 for the exact fixed versions and upgrade guidance. Apply updates during the next available maintenance window and validate service functionality after upgrade.

Workarounds

Place the FortiClientEMS management interface behind a VPN or firewall rule set that blocks untrusted networks
Deploy a reverse proxy or web application firewall configured to reject requests containing path traversal sequences in upload parameters
Enforce least privilege on the FortiClientEMS service account to limit the scope of any successful file write

bash

# Example WAF rule concept to block traversal in upload parameters
# Deny requests where the filename parameter contains ../ or encoded variants
SecRule ARGS:filename "@rx (\.\./|\.\.\\|%2e%2e[/\\%])" \
    "id:1002259,phase:2,deny,status:400,log,msg:'FortiClientEMS path traversal attempt CVE-2025-22859'"