Siemens SIMATIC CN 4100 Critical Vulnerabilities (CVSS 9.6) — Detection and Mitigation

Siemens has released a critical advisory for SIMATIC CN 4100 devices, flagging multiple high-severity vulnerabilities that impact the Confidentiality, Integrity, and Availability (CIA) of these industrial controllers. With a CVSS v3 score of 9.6, these flaws—including memory corruption issues like Stack-based Buffer Overflow and Use-After-Free—pose a significant risk to operational technology (OT) environments.

For defenders, this is not a theoretical exercise. Successful exploitation of these vulnerabilities could allow an attacker to crash the controller (Denial of Service) or potentially execute arbitrary code, disrupting industrial processes. If your environment utilizes SIMATIC CN 4100 versions prior to 5.0, this bulletin requires immediate action to validate your asset inventory and apply the necessary updates.

Technical Analysis

Affected Product:

• Siemens SIMATIC CN 4100

Affected Versions:

• All versions prior to 5.0 (vers:intdot/<5.0)

Vulnerability Types: The advisory identifies a constellation of memory safety and logic flaws, including:

• Stack-based Buffer Overflow: Allows overwriting the execution stack, potentially leading to Remote Code Execution (RCE).
• Use After Free: Dereferencing memory after it has been freed, leading to crashes or code execution.
• Out-of-bounds Read/Write: Reading or writing memory past the intended buffer boundaries.
• Allocation of Resources Without Limits: Vulnerable to resource exhaustion attacks (DoS).
• Integer Overflow or Wraparound: Logic errors that can bypass security checks.

Exploitation Risks: While specific public proof-of-concept (PoC) code is not detailed in the immediate release, the nature of these vulnerabilities (memory corruption) suggests that reliable exploitation is feasible for sophisticated actors. In ICS environments, the primary attack vector typically involves crafted packets sent to the controller's network interfaces (often S7Comm or Profinet related ports).

CVSS Score: 9.6 (Critical)

Detection & Response

Detecting exploitation attempts against ICS devices requires a layered approach. Since we cannot deploy endpoint agents directly on the PLC, we focus on network anomalies and the Engineering Workstations (EWs) that manage them.

SIGMA Rules

The following Sigma rules focus on detecting suspicious network interactions with SIMATIC devices and anomalies on the engineering workstations that might indicate a successful compromise or an active exploitation attempt.

---
title: Potential Exploit Activity - Siemens S7Comm Port Access
id: 8f4a2b1c-6d9e-4a3f-9c1d-2e4f5a6b7c8d
status: experimental
description: Detects inbound network connections to Siemens S7Comm ports (TCP 102) from non-standard engineering workstations. Exploits against SIMATIC controllers often target these ports.
references:
  - https://www.cisa.gov/news-events/ics-advisories/icsa-26-134-10
author: Security Arsenal
date: 2026/05/15
tags:
  - attack.initial_access
  - attack.t1190
  - ics
logsource:
  category: network_connection
  product: windows
detection:
  selection:
    DestinationPort: 102
    Initiated: false
  filter:
    SourceIp|startswith:
      - '192.168.' # Internal Engineering Subnet - adjust to your environment
      - '10.0.'
  condition: selection and not filter
falsepositives:
  - Legitimate traffic from new engineering workstations
level: high
---
title: Siemens Engineering Workstation - Suspicious Process Spawn
id: 9e5c3d2a-7e0f-5b4g-0d2e-3f5g6h7i8j9k
status: experimental
description: Detects suspicious processes (cmd, powershell) spawned by the Siemens automation service (s7oiehsx.exe). This may indicate a successful exploit or lateral movement from the engineering station.
references:
  - https://www.cisa.gov/news-events/ics-advisories/icsa-26-134-10
author: Security Arsenal
date: 2026/05/15
tags:
  - attack.execution
  - attack.t1059.001
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    ParentImage|endswith: '\s7oiehsx.exe'
    Image|endswith:
      - '\cmd.exe'
      - '\powershell.exe'
      - '\pwsh.exe'
falsepositives:
  - Legitimate administrative scripts run by engineers
level: high

KQL (Microsoft Sentinel)

This KQL query hunts for unusual network traffic volumes to the specific IP ranges where SIMATIC CN 4100 devices are hosted, which could indicate resource exhaustion attacks or scanning attempts.

let SiemensPLC_IP_Ranges = dynamic(["192.168.10.0/24", "10.20.30.0/24"]); // Define your OT subnets
DeviceNetworkEvents
| where ipv4_is_in_range(DeviceAddress, SiemensPLC_IP_Ranges)
| where RemotePort in (102, 80, 443) // Common S7/Web management ports
| summarize Count = count(), BytesSent = sum(SentBytes), BytesReceived = sum(ReceivedBytes) by DeviceAddress, RemoteIP, RemotePort, bin(Timestamp, 5m)
| where Count > 100 // Threshold for high-frequency connection attempts indicating scanning or flooding
| project Timestamp, DeviceAddress, RemoteIP, RemotePort, Count, BytesSent, BytesReceived
| order by Timestamp desc

Velociraptor VQL

This artifact hunts for established network connections on the Engineering Workstation that are communicating with the PLC ports, useful for identifying active sessions during an incident response.

-- Hunt for active connections to Siemens S7Comm ports
SELECT Fd.Address, Fd.Port, Pid, Name, Username, Started
FROM listen()
WHERE Port = 102
   OR Port = 161 // SNMP often used for management

Remediation Script (PowerShell)

Use this PowerShell script on Windows-based Engineering Workstations or Jump Servers to enforce network segmentation as an immediate mitigation if patching is delayed. It creates a firewall rule to block inbound S7Comm traffic from unauthorized subnets.

# Remediation: Restrict S7Comm Access on Management Station
# Usage: Run with Administrator privileges

$RuleName = "Block-Unauthorized-S7Comm-Inbound"
$AuthorizedSubnets = @("192.168.10.0/24", "10.0.0.0/8") # Define trusted subnets

# Check if rule exists
$existingRule = Get-NetFirewallRule -DisplayName $RuleName -ErrorAction SilentlyContinue

if (-not $existingRule) {
    Write-Host "Creating Firewall Rule: $RuleName"
    New-NetFirewallRule -DisplayName $RuleName `
                       -Direction Inbound `
                       -Protocol TCP `
                       -LocalPort 102 `
                       -Action Block `
                       -Profile Any `
                       -Description "Block unauthorized S7Comm traffic. Authorized subnets are handled by specific allow rules."
    Write-Host "Base block rule created."
} else {
    Write-Host "Rule '$RuleName' already exists."
}

# Ensure Allow rules for authorized subnets exist (Implementation depends on environment)
# This script ensures the default is BLOCK unless explicitly allowed.

Remediation

To effectively mitigate these vulnerabilities, Security Arsenal recommends the following actions:

1. Patch Immediately: Update SIMATIC CN 4100 devices to the latest firmware version. The vendor states that versions prior to 5.0 are affected. Ensure updates are tested in a non-production environment first to validate process compatibility.
2. Network Segmentation: Ensure SIMATIC CN 4100 devices are placed in a dedicated VLAN (OT Zone) with strict access control lists (ACLs) limiting traffic to only known Engineering Workstations and HMIs. Block access to TCP/102 and TCP/80/443 from the IT network and Internet.
3. Review Configuration: Check if "Allocation of Resources Without Limits" can be mitigated by configuring device-level limits for connections or sessions, if supported by the firmware.
4. Monitor for Anomalies: Deploy the detection rules provided above to your SIEM to identify scanning or exploitation attempts immediately.

Official Vendor Advisory: Siemens Security Advisory

Related Resources

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