CVE-2026-22925: SIMATIC CN 4100 DoS Vulnerability

CVE-2026-22925 Overview

CVE-2026-22925 is a resource exhaustion vulnerability affecting Siemens SIMATIC CN 4100 devices running firmware versions prior to V5.0. The flaw allows an unauthenticated remote attacker to send a high volume of TCP SYN packets, overwhelming system resources and triggering denial-of-service conditions. The vulnerability is tracked under CWE-770: Allocation of Resources Without Limits or Throttling.

Successful exploitation renders the affected industrial communication node unavailable, disrupting connectivity to managed assets. Siemens disclosed the issue in advisory SSA-032379 and released firmware V5.0 as the corrective update.

Critical Impact

Unauthenticated attackers can remotely disable SIMATIC CN 4100 devices through TCP SYN flooding, interrupting industrial network communications.

Affected Products

• Siemens SIMATIC CN 4100 (all versions prior to V5.0)

Discovery Timeline

• 2026-05-12 - CVE-2026-22925 published to NVD
• 2026-05-12 - Last updated in NVD database

Technical Details for CVE-2026-22925

Vulnerability Analysis

The SIMATIC CN 4100 is an industrial communication node used in operational technology (OT) environments to manage connectivity between control systems. The affected firmware fails to enforce limits on the resources consumed when processing inbound TCP SYN packets. An attacker who can reach the device over the network can saturate the TCP connection backlog or memory allocator by transmitting SYN packets faster than the device can complete or expire half-open connections.

The weakness is classified as CWE-770: Allocation of Resources Without Limits or Throttling. The TCP stack on the device does not apply adequate rate limiting, SYN cookies, or backlog reaping under load.

Root Cause

The root cause is missing throttling on TCP connection establishment. When a SYN packet arrives, the device allocates state for the half-open connection. Without a hard ceiling or eviction policy, sustained SYN traffic exhausts the connection table and any associated memory pools. Legitimate sessions cannot be established once the resource pool is depleted.

Attack Vector

Exploitation requires only network reachability to a TCP port on the device. The attacker does not need credentials, user interaction, or prior access. A standard SYN flood tool generates the traffic pattern needed to trigger the condition. Because OT networks frequently expose management or communication ports across flat VLANs, attackers with a foothold elsewhere in the environment can reach the device. The vulnerability does not permit code execution or data disclosure. Impact is limited to availability of the affected service.

No public proof-of-concept code or exploit has been linked to this CVE. The technique itself, however, relies on well-documented SYN flooding methodology that requires no novel tooling. See the Siemens Security Advisory SSA-032379 for vendor-supplied technical detail.

Detection Methods for CVE-2026-22925

Indicators of Compromise

• Sustained high volumes of inbound TCP SYN packets directed at SIMATIC CN 4100 device IPs without corresponding ACK completion.
• Loss of communication or heartbeat alarms from SIMATIC CN 4100 nodes coinciding with elevated network traffic.
• SNMP or syslog entries from network switches showing port saturation toward the affected device.

Detection Strategies

• Deploy network IDS signatures that flag SYN flood patterns, such as a high SYN-to-SYN/ACK ratio per source or per destination over short intervals.
• Baseline normal TCP session establishment rates for OT segments and alert on deviations directed at SIMATIC CN 4100 assets.
• Correlate device availability telemetry with upstream network flow records to identify denial-of-service events.

Monitoring Recommendations

• Forward NetFlow, IPFIX, or sFlow data from OT-adjacent switches into a SIEM for continuous flow analysis.
• Monitor ICS asset inventory tools for offline events on SIMATIC CN 4100 devices and trigger investigation playbooks.
• Track ARP and TCP state-table utilization on perimeter firewalls protecting the OT segment.

How to Mitigate CVE-2026-22925

Immediate Actions Required

• Inventory all SIMATIC CN 4100 devices and identify firmware versions below V5.0.
• Update affected devices to firmware V5.0 or later as published by Siemens.
• Restrict network access to the device to engineering workstations and authorized peers only.
• Place SIMATIC CN 4100 assets behind a stateful firewall that performs SYN flood protection or SYN cookies.

Patch Information

Siemens has released firmware V5.0 for the SIMATIC CN 4100. Operators should apply the update following standard OT change-control procedures. Full remediation guidance is provided in the Siemens Security Advisory SSA-032379.

Workarounds

• Segment SIMATIC CN 4100 devices into a dedicated VLAN with strict access control lists permitting only required source addresses and ports.
• Enable SYN flood mitigation features on upstream firewalls, including connection rate limiting and SYN proxying.
• Apply Siemens operational security guidelines for SIMATIC environments, including defense-in-depth and cell protection concepts.

# Example upstream firewall rate-limit rule (iptables syntax)
iptables -A FORWARD -p tcp --syn -d <SIMATIC_CN4100_IP> \
  -m connlimit --connlimit-above 50 --connlimit-mask 32 -j DROP
iptables -A FORWARD -p tcp --syn -d <SIMATIC_CN4100_IP> \
  -m limit --limit 25/s --limit-burst 50 -j ACCEPT