---
title: "Critical Siemens IP-Stack Flaw Exposes Industrial Systems to DoS Attacks"
short_title: "Siemens IP-Stack vulnerability threatens industrial systems"
description: "Siemens warns of a high-severity flaw (CVE-2025-40820) in its Interniche IP-Stack, enabling remote DoS attacks on industrial products. Patch now."
author: "Vitus"
date: 2025-01-24
categories: [Cybersecurity, Vulnerabilities]
tags: [siemens, cve-2025-40820, industrial-security, dos, tcp-ip]
score: 0.85
cve_ids: [CVE-2025-40820]
---
TL;DR
Siemens has disclosed a high-severity vulnerability (CVE-2025-40820) in its Interniche IP-Stack, affecting over 100 industrial products. The flaw allows unauthenticated remote attackers to disrupt TCP-based services, potentially causing denial-of-service (DoS) conditions. Siemens has released patches for some products and recommends mitigation steps for unpatched systems.
---
Main Content
Critical Siemens IP-Stack Vulnerability Threatens Industrial Operations
A newly discovered vulnerability in Siemens’ Interniche IP-Stack exposes a wide range of industrial products to remote denial-of-service (DoS) attacks. Tracked as CVE-2025-40820, the flaw stems from improper TCP sequence number validation, enabling attackers to interfere with connection setups if they can inject spoofed IP packets at precise moments. With a CVSS score of 7.5, this issue poses a significant risk to critical manufacturing infrastructure worldwide.
---
Key Points
- Vulnerability: CVE-2025-40820 affects Siemens’ Interniche IP-Stack, allowing unauthenticated remote attackers to disrupt TCP-based services.
- Impact: Successful exploitation could lead to DoS conditions, affecting industrial operations reliant on Siemens products.
- Affected Systems: Over 100 Siemens products, including SIMATIC PLCs, SIDOOR access control systems, and SINUMERIK CNC controllers.
- Mitigation: Siemens has released patches for some products and recommends disabling Ethernet ports or limiting TCP accessibility to trusted IPs where fixes are unavailable.
- Severity: Rated 7.5 (High) on the CVSS scale, highlighting its potential for widespread disruption.
---
Technical Details
The vulnerability arises from improper validation of TCP sequence numbers in Siemens’ Interniche IP-Stack. Under specific conditions, the stack accepts a broad range of sequence values, allowing attackers to spoof IP packets and interfere with connection setups. This flaw exclusively affects TCP-based services, meaning systems relying on UDP or other protocols remain unaffected.
Exploitation Requirements:
- Attackers must inject spoofed IP packets into the network.
- Timing is critical—packets must be sent at precise moments during connection setup.
- Only TCP-based services are vulnerable, limiting the attack surface but not eliminating the risk.
---
Impact Assessment
The flaw’s high severity stems from its potential to disrupt industrial operations in critical sectors such as manufacturing. Siemens products are widely deployed in automation, energy, and transportation, making this vulnerability a prime target for threat actors seeking to cause operational downtime.
While the attack requires specific conditions (e.g., spoofed packets and precise timing), the widespread use of Siemens products amplifies the risk. Organizations unable to patch immediately should isolate affected systems and restrict network access to mitigate exposure.
---
Mitigation Steps
Siemens has released patches for several affected products and is preparing additional fixes. For systems where updates are not yet available, the following measures are recommended:
1. Disable Ethernet Ports: Use communication modules (e.g., CP) instead of CPU Ethernet ports for network connectivity.
2. Restrict TCP Access: Limit TCP accessibility to trusted IP addresses only.
3. Network Segmentation: Isolate industrial control systems (ICS) from business networks using firewalls.
4. Monitor for Exploitation: Deploy intrusion detection systems (IDS) to detect unusual TCP traffic patterns.
For a full list of affected products and patch availability, refer to Siemens’ [official advisory](https://github.com/cisagov/CSAF/blob/develop/csaf_files/OT/white/2025/icsa-25-352-05.json).
---
Affected Systems
The vulnerability impacts a broad range of Siemens industrial products, including:
- SIMATIC PLCs (S7-1200, S7-1500, S7-300, S7-400 series)
- SIDOOR access control systems (ATD430W, ATE530G, ATE530S)
- SINUMERIK CNC controllers (840D sl)
- ET 200 distributed I/O systems (ET 200AL, ET 200SP, ET 200pro)
- SIWAREX weighing systems (WP231, WP241, WP251, WP521, WP522)
- SIPLUS ruggedized variants of the above products
A complete list of affected products is available in the [CSAF advisory](https://github.com/cisagov/CSAF/blob/develop/csaf_files/OT/white/2025/icsa-25-352-05.json).
---
Conclusion
CVE-2025-40820 underscores the critical importance of securing industrial networks against TCP-based attacks. While Siemens has taken steps to address the flaw, organizations must act swiftly to apply patches or implement mitigations to prevent potential disruptions. Given the widespread deployment of affected products, this vulnerability could have far-reaching consequences if left unaddressed.
For further guidance, consult Siemens’ [Industrial Security Guidelines](https://www.siemens.com/cert/operational-guidelines-industrial-security) or contact the [Siemens ProductCERT](https://www.siemens.com/cert/advisories).
---
References
[^1]: Siemens ProductCERT. "[ICSA-25-352-05: Siemens Interniche IP-Stack Vulnerability](https://github.com/cisagov/CSAF/blob/develop/csaf_files/OT/white/2025/icsa-25-352-05.json)". Retrieved 2025-01-24.
[^2]: CISA. "[ICS Advisory ICSA-25-352-05](https://www.cisa.gov/news-events/ics-advisories/icsa-25-352-05)". Retrieved 2025-01-24.
[^3]: NIST. "[CVE-2025-40820 Detail](https://nvd.nist.gov/vuln/detail/CVE-2025-40820)". Retrieved 2025-01-24.
[^4]: MITRE. "[CWE-940: Improper Verification of Source of a Communication Channel](https://cwe.mitre.org/data/definitions/940.html)". Retrieved 2025-01-24.