CVE-2025-53951 Overview
CVE-2025-53951 is a path traversal vulnerability [CWE-22] affecting the Fortinet FortiDLP Agent Outlookproxy plugin on Windows. The flaw allows an authenticated local attacker to escalate privileges to LocalService by sending a crafted request to a local listening port used by the plugin.
Fortinet published advisory FG-IR-25-628 covering this issue. The vulnerability affects multiple FortiDLP Agent branches spanning versions 10.3.1 through 11.5.1.
Critical Impact
An authenticated attacker on an affected Windows endpoint can escalate to the LocalService account, gaining elevated code execution and access to protected local resources.
Affected Products
- Fortinet FortiDLP Agent 11.5.1, 11.4.2 through 11.4.6, 11.3.2 through 11.3.4, 11.2.0 through 11.2.3, 11.1.1 through 11.1.2, 11.0.1
- Fortinet FortiDLP Agent 10.5.1, 10.4.0, 10.3.1
- Microsoft Windows (FortiDLP Agent Outlookproxy plugin deployments)
Discovery Timeline
- 2025-10-16 - CVE-2025-53951 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-53951
Vulnerability Analysis
The FortiDLP Agent Outlookproxy plugin exposes a local listening port on Windows hosts to service inter-process communication with Outlook and other local components. The plugin fails to properly normalize and validate pathname inputs before using them in filesystem operations executed under the LocalService account.
Because the plugin runs privileged operations on behalf of local requesters, a low-privileged authenticated user on the host can craft requests containing traversal sequences to reach files and code outside the intended directory scope. Successful exploitation yields confidentiality, integrity, and availability impact on the target endpoint. Exploitation requires local access and low privileges, with no user interaction.
Root Cause
The root cause is Improper Limitation of a Pathname to a Restricted Directory [CWE-22]. The Outlookproxy plugin accepts path parameters through its local IPC channel without canonicalizing them or enforcing a directory allowlist. Traversal sequences such as ..\ can escape the intended working directory and reference attacker-controlled locations that the privileged plugin process then reads or writes.
Attack Vector
An attacker with an authenticated session on the Windows endpoint connects to the local port exposed by the Outlookproxy plugin. The attacker submits a crafted request containing a manipulated pathname. The plugin, running as LocalService, performs the requested filesystem operation on the traversal target, allowing the attacker to place, replace, or read files that lead to privilege escalation to LocalService.
No verified public exploit code is available. Refer to the Fortinet Security Advisory FG-IR-25-628 for vendor-supplied technical details.
Detection Methods for CVE-2025-53951
Indicators of Compromise
- Unexpected child processes or file writes originating from the FortiDLP Agent Outlookproxy process running under the LocalService account.
- Files created or modified under FortiDLP directories that contain path traversal sequences (..\) in log entries or request captures.
- Local TCP connections from non-Outlook user-mode processes to the Outlookproxy plugin's listening port.
Detection Strategies
- Monitor for anomalous filesystem writes by the FortiDLP Agent process tree to paths outside its installation directory.
- Alert on process launches under NT AUTHORITY\LocalService that were spawned by the Outlookproxy plugin and execute non-standard binaries.
- Correlate local loopback connections to FortiDLP listening ports with the identity of the connecting user process.
Monitoring Recommendations
- Enable Windows Sysmon Event IDs 1 (process create), 11 (file create), and 3 (network connect) with rules scoped to FortiDLP components.
- Baseline the expected callers of the Outlookproxy local port and flag deviations.
- Ingest endpoint telemetry into a centralized data lake to hunt for traversal patterns across the fleet.
How to Mitigate CVE-2025-53951
Immediate Actions Required
- Inventory all Windows endpoints running FortiDLP Agent and identify installations matching the affected version list.
- Upgrade FortiDLP Agent to a fixed release as documented in FG-IR-25-628.
- Restrict interactive and remote logon rights on endpoints where the agent is deployed to reduce the population of potential local attackers.
Patch Information
Fortinet has published remediation guidance in the Fortinet Security Advisory FG-IR-25-628. Administrators should consult the advisory for the specific fixed build for each affected branch and deploy through their standard endpoint management tooling.
Workarounds
- If immediate patching is not feasible, disable the Outlookproxy plugin on managed endpoints per vendor guidance.
- Apply host-based firewall rules restricting access to the plugin's local listening port to trusted processes only.
- Enforce least-privilege on Windows endpoints to limit which accounts can authenticate locally and reach the vulnerable IPC channel.
# Configuration example
# Query installed FortiDLP Agent version on a Windows host via PowerShell
Get-CimInstance -ClassName Win32_Product | Where-Object { $_.Name -like '*FortiDLP*' } | Select-Object Name, Version
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
