Multiple Siemens industrial products are affected by CVE-2025-40820, a vulnerability in the InterNiche IP-Stack that allows unauthenticated remote attackers to interfere with TCP connection setup, potentially causing denial of service. The vulnerability affects TCP sequence number validation and impacts over 140 different Siemens products including SIMATIC S7 series, ET 200 series, and other industrial automation systems. Attacks require precise timing and spoofed IP packets. Siemens has released fixes for some products and recommends specific countermeasures for others.