As of January 10, 2023, CISA will no longer be updating ICS security advisories for Siemens product vulnerabilities beyond the initial advisory. For the most up-to-date information on vulnerabilities in this advisory, please see Siemens’ ProductCERT Security Advisories (CERT Services | Services | Siemens Global).
1. EXECUTIVE SUMMARY
- CVSS v4 8.7
- ATTENTION: Exploitable from adjacent network/low attack complexity
- Vendor: Siemens
- Equipment: SINUMERIK
- Vulnerability: Authentication Bypass Using an Alternate Path or Channel
2. RISK EVALUATION
Successful exploitation of this vulnerability could allow an attacker to gain unauthorized remote access and potentially compromise system confidentiality, integrity, or availability.
3. TECHNICAL DETAILS
3.1 AFFECTED PRODUCTS
Siemens reports that the following products are affected:
- SINUMERIK 828D PPU.4: Versions prior to V4.95 SP5
- SINUMERIK 828D PPU.5: Versions prior to V5.25 SP1
- SINUMERIK 840D sl: Versions prior to V4.95 SP5
- SINUMERIK MC: Versions prior to V1.25 SP1
- SINUMERIK MC V1.15: Versions prior to V1.15 SP5
- SINUMERIK ONE: Versions prior to V6.25 SP1
- SINUMERIK ONE V6.15: Versions prior to V6.15 SP5
3.2 VULNERABILITY OVERVIEW
3.2.1 AUTHENTICATION BYPASS USING AN ALTERNATE PATH OR CHANNEL CWE-288
The affected application improperly validates authentication for its VNC access service, allowing access with insufficient password verification. This could allow an attacker to gain unauthorized remote access and potentially compromise system confidentiality, integrity, or availability.
CVE-2025-40743 has been assigned to this vulnerability. A CVSS v3.1 base score of 8.3 has been calculated; the CVSS vector string is (CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L).
A CVSS v4 score has also been calculated for CVE-2025-40743. A base score of 8.7 has been calculated; the CVSS vector string is (CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N).
3.3 BACKGROUND
- CRITICAL INFRASTRUCTURE SECTORS: Critical Manufacturing
- COUNTRIES/AREAS DEPLOYED: Worldwide
- COMPANY HEADQUARTERS LOCATION: Germany
3.4 RESEARCHER
Siemens reported this vulnerability to CISA.
4. MITIGATIONS
Siemens has identified the following specific workarounds and mitigations users can apply to reduce risk:
- Apply Defense-in-Depth.
- Close VNC port on X130 via HMI setting.
- Set VNC Password on X120 and X130.
- Change TCU.ini setting to “ExternalViewerReqTimeoutMode=0”.
- SINUMERIK MC V1.15: Update to V1.15 SP5 or later version.
- SINUMERIK MC: Update to V1.25 SP1 or later version.
- SINUMERIK 840D sl: Update to V4.95 SP5 or later version.
- SINUMERIK 828D PPU.4: Update to V4.95 SP5 or later version.
- SINUMERIK 828D PPU.5: Update to V5.25 SP1 or later version.
- SINUMERIK ONE V6.15: Update to V6.15 SP5 or later version.
- SINUMERIK ONE: Update to V6.25 SP1 or later version.
- Updated software version can be obtained from Siemens customer support or a local partner.
As a general security measure, Siemens recommends protecting network access to devices with appropriate mechanisms. To operate the devices in a protected IT environment, Siemens recommends configuring the environment according to Siemens’ operational guidelines for industrial security and following recommendations in the product manuals.
Additional information on industrial security by Siemens can be found on the Siemens industrial security webpage.
For more information see the associated Siemens security advisory SSA-177847 in HTML and CSAF.
CISA recommends users take defensive measures to minimize the risk of exploitation of this vulnerability, such as:
- Minimize network exposure for all control system devices and/or systems, ensuring they are not accessible from the internet.
- Locate control system networks and remote devices behind firewalls and isolating them from business networks.
- When remote access is required, use more secure methods, such as Virtual Private Networks (VPNs). Recognize VPNs may have vulnerabilities, should be updated to the most recent version available, and are only as secure as the connected devices.
CISA reminds organizations to perform proper impact analysis and risk assessment prior to deploying defensive measures.
CISA also provides a section for control systems security recommended practices on the ICS webpage on cisa.gov. Several CISA products detailing cyber defense best practices are available for reading and download, including Improving Industrial Control Systems Cybersecurity with Defense-in-Depth Strategies.
CISA encourages organizations to implement recommended cybersecurity strategies for proactive defense of ICS assets.
Additional mitigation guidance and recommended practices are publicly available on the ICS webpage at cisa.gov in the technical information paper, ICS-TIP-12-146-01B–Targeted Cyber Intrusion Detection and Mitigation Strategies.
Organizations observing suspected malicious activity should follow established internal procedures and report findings to CISA for tracking and correlation against other incidents.
CISA also recommends users take the following measures to protect themselves from social engineering attacks:
- Do not click web links or open attachments in unsolicited email messages.
- Refer to Recognizing and Avoiding Email Scams for more information on avoiding email scams.
- Refer to Avoiding Social Engineering and Phishing Attacks for more information on social engineering attacks.
No known public exploitation specifically targeting this vulnerability has been reported to CISA at this time. This vulnerability is not exploitable remotely.
5. UPDATE HISTORY
- August 14, 2025: Initial Republication of Siemens SSA-177847