CVE-2025-40738: Siemens Sinec NMS Path Traversal Flaw

CVE-2025-40738 Overview

CVE-2025-40738 is a path traversal vulnerability in Siemens SINEC NMS (Network Management System) affecting all versions before V4.0. The application fails to validate file paths during ZIP archive extraction, enabling attackers to write files outside the intended extraction directory. Successful exploitation allows arbitrary file write to restricted locations and can lead to code execution with elevated privileges. The flaw is tracked as ZDI-CAN-26572 and falls under [CWE-22] Improper Limitation of a Pathname to a Restricted Directory. Authenticated network-adjacent attackers can trigger the issue by uploading a crafted ZIP file to the affected component.

Critical Impact
Authenticated attackers can write arbitrary files to restricted directories on the SINEC NMS host and execute code with elevated privileges, compromising industrial network management infrastructure.

Affected Products

Siemens SINEC NMS — all versions prior to V4.0
Siemens industrial network monitoring deployments using SINEC NMS
Operational Technology (OT) environments managed via SINEC NMS

Discovery Timeline

2025-07-08 - CVE-2025-40738 published to NVD
2025-08-21 - Last updated in NVD database

Technical Details for CVE-2025-40738

Vulnerability Analysis

The vulnerability resides in the ZIP archive extraction logic of SINEC NMS. The application processes uploaded archives without verifying that entry file paths remain within the designated extraction directory. An attacker crafts a ZIP archive containing entries with traversal sequences such as ../ in their filenames. When SINEC NMS extracts the archive, the application writes those entries to attacker-controlled locations on the file system.

This class of flaw is commonly referred to as a Zip Slip vulnerability. Because SINEC NMS runs with elevated privileges to manage network devices, files written through this primitive can overwrite binaries, configuration files, scheduled task definitions, or web application content. Replacing one of these targets converts the file write into code execution under the service account context.

The attack vector is network-based and requires low-privileged authentication. No user interaction is required to trigger the extraction once an archive is uploaded through the supported workflow. EPSS data places exploitation probability at 1.72% with an 82.7 percentile ranking, indicating elevated exploitation likelihood compared to the broader CVE population.

Root Cause

The root cause is missing canonicalization and validation of ZIP entry paths before file system writes. The extraction routine concatenates the target directory with the archive entry name without resolving relative path components or comparing the resulting path against the intended base directory.

Attack Vector

An authenticated attacker uploads a malicious ZIP archive to the SINEC NMS application through a supported upload endpoint. The archive contains entries with names such as ..\..\Windows\System32\config\target.dll or paths targeting service binaries. During extraction, SINEC NMS writes the entries to attacker-chosen locations, enabling arbitrary file write and privileged code execution.

No public proof-of-concept exploit is available at the time of publication. Refer to the Siemens Security Advisory SSA-078892 for vendor-provided technical context.

Detection Methods for CVE-2025-40738

Indicators of Compromise

Unexpected files appearing in SINEC NMS installation directories, service binary paths, or system folders following ZIP upload activity
ZIP archives stored or processed by SINEC NMS containing entries with ..\ or ../ path traversal sequences
New or modified scheduled tasks, services, or startup entries created by the SINEC NMS service account
Anomalous child processes spawned by the SINEC NMS process tree following an archive upload

Detection Strategies

Inspect file system audit logs for write operations by the SINEC NMS service account outside its designated data directories
Parse stored ZIP archives processed by SINEC NMS and flag entries whose canonicalized paths escape the intended extraction root
Monitor SINEC NMS application logs for upload events correlated with file creation in privileged paths
Apply behavioral identification on the host to flag the SINEC NMS process writing executable content or modifying system directories

Monitoring Recommendations

Forward SINEC NMS application and Windows Security event logs to a centralized SIEM for correlation of upload and file-write events
Establish baselines for legitimate file activity by the SINEC NMS service account and alert on deviations
Track authentication events to SINEC NMS and correlate low-privileged sessions with subsequent file system changes

How to Mitigate CVE-2025-40738

Immediate Actions Required

Upgrade SINEC NMS to version V4.0 or later as directed in Siemens Security Advisory SSA-078892
Restrict network access to SINEC NMS management interfaces to trusted administrative networks only
Review and rotate credentials for any SINEC NMS accounts that may have been exposed to untrusted users
Audit the SINEC NMS host for unauthorized files written outside expected data directories

Patch Information

Siemens has released SINEC NMS V4.0, which remediates the path traversal flaw during ZIP extraction. Customers running any version below V4.0 should plan an upgrade window. The vendor advisory SSA-078892 lists the fixed release and provides upgrade instructions.

Workarounds

Limit access to the SINEC NMS upload functionality to a minimal set of trusted administrators until patching is complete
Place SINEC NMS behind network segmentation controls that block exposure to general corporate or OT user networks
Enforce least-privilege configuration for SINEC NMS service accounts where supported by the deployment
Apply Siemens operational guidelines for securing industrial environments, including defense-in-depth network architecture

bash

# No vendor-supplied configuration mitigation is available;
# the supported remediation is upgrading SINEC NMS to V4.0 or later.
# Reference: https://cert-portal.siemens.com/productcert/html/ssa-078892.html