CVE-2026-25655: Siemens SINEC NMS RCE Vulnerability

CVE-2026-25655 Overview

A vulnerability has been identified in Siemens SINEC NMS (All versions < V4.0 SP2) that permits improper modification of a configuration file by a low-privileged user. This security flaw could allow an attacker to load malicious DLLs, potentially leading to arbitrary code execution with administrative privileges. The vulnerability is tracked under ZDI-CAN-28107 and represents a significant privilege escalation risk in affected network management system deployments.

Critical Impact

Low-privileged attackers can achieve arbitrary code execution with administrative privileges through DLL hijacking, potentially compromising the entire network management infrastructure.

Affected Products

• Siemens SINEC NMS (All versions prior to V4.0 SP2)
• Siemens SINEC NMS V4.0
• Siemens SINEC NMS V4.0 SP1

Discovery Timeline

• 2026-02-10 - CVE-2026-25655 published to NVD
• 2026-02-12 - Last updated in NVD database

Technical Details for CVE-2026-25655

Vulnerability Analysis

This vulnerability falls under CWE-427 (Uncontrolled Search Path Element), commonly known as DLL hijacking or DLL search order hijacking. The affected SINEC NMS application fails to properly restrict modifications to configuration files that control how dynamic link libraries are loaded. A user with low-level privileges on the system can manipulate these configuration settings to specify malicious DLL paths, causing the application to load attacker-controlled code.

The local attack vector indicates that an attacker must already have some level of access to the target system. However, the low privilege requirement significantly lowers the barrier to exploitation—standard user accounts without administrative rights can exploit this vulnerability. Once exploited, the attacker gains code execution in the context of the SINEC NMS application, which typically runs with elevated administrative privileges to perform network management functions.

Root Cause

The root cause of this vulnerability lies in insecure file permissions and inadequate access controls on configuration files used by SINEC NMS. The application trusts configuration data that can be modified by low-privileged users, allowing attackers to inject references to malicious DLL files. When the application subsequently loads these DLLs, the malicious code executes with the application's elevated privileges, resulting in a privilege escalation attack.

Attack Vector

The attack requires local access to a system running a vulnerable version of SINEC NMS. An attacker with low-privilege access can:

1. Identify the vulnerable configuration file that controls DLL loading behavior
2. Modify the configuration to point to a malicious DLL placed in an attacker-controlled location
3. Trigger the application to reload its configuration or wait for a service restart
4. The malicious DLL is loaded and executed with administrative privileges

The attack does not require user interaction and has low complexity, making it relatively straightforward to exploit once an attacker has established a foothold on the target system. For detailed technical information, refer to the Siemens Security Advisory.

Detection Methods for CVE-2026-25655

Indicators of Compromise

• Unexpected modifications to SINEC NMS configuration files, particularly those controlling library paths or DLL loading behavior
• Presence of unsigned or suspicious DLL files in non-standard directories accessible to the SINEC NMS application
• Process execution anomalies where SINEC NMS spawns unexpected child processes or loads unusual modules
• File system access patterns showing low-privileged users modifying application configuration files

Detection Strategies

• Implement file integrity monitoring (FIM) on SINEC NMS configuration directories to detect unauthorized modifications
• Monitor Windows Event Logs for DLL loading events associated with the SINEC NMS process, particularly from unusual paths
• Deploy endpoint detection and response (EDR) solutions configured to alert on privilege escalation patterns and DLL sideloading techniques
• Audit user access to SINEC NMS installation directories and configuration files

Monitoring Recommendations

• Enable detailed audit logging for file access and modification events on the SINEC NMS installation directory
• Configure SIEM rules to correlate low-privileged user activity with subsequent SINEC NMS configuration changes
• Monitor for unsigned DLL loads by the SINEC NMS process using application whitelisting or code signing validation tools
• Establish baseline behavior for SINEC NMS DLL loading patterns to detect anomalous library loads

How to Mitigate CVE-2026-25655

Immediate Actions Required

• Upgrade Siemens SINEC NMS to version V4.0 SP2 or later immediately
• Review and restrict file system permissions on SINEC NMS configuration files to prevent modification by low-privileged users
• Audit systems for signs of exploitation, including unexpected DLL files or configuration changes
• Implement network segmentation to limit access to systems running SINEC NMS

Patch Information

Siemens has released SINEC NMS V4.0 SP2 which addresses this vulnerability. Organizations should obtain the patch through official Siemens channels and apply it following their change management procedures. Detailed patch information and download links are available in the Siemens Security Advisory SSA-311973.

Workarounds

• Restrict file system permissions on SINEC NMS configuration directories to prevent write access by non-administrative users
• Implement application whitelisting to prevent unauthorized DLLs from being loaded by the SINEC NMS process
• Use Windows Security features such as Protected Process Light (PPL) or Code Integrity policies where applicable
• Limit local access to systems running SINEC NMS to only essential personnel with legitimate business needs

# Example: Restrict configuration file permissions (Windows)
# Run as Administrator - adjust path as needed for your installation
icacls "C:\Program Files\Siemens\SINEC NMS\config" /inheritance:r /grant:r "SYSTEM:(OI)(CI)F" /grant:r "Administrators:(OI)(CI)F"