CVE-2024-32740: Siemens SIMATIC CN 4100 Auth Bypass Flaw

CVE-2024-32740 Overview

CVE-2024-32740 affects Siemens SIMATIC CN 4100 industrial communication devices running firmware versions prior to V3.0. The device ships with undocumented user accounts and embedded credentials [CWE-798]. An attacker who learns these credentials can authenticate locally or across the network and gain control of the device. Siemens disclosed the issue in advisory SSA-273900. The vulnerability falls into the Hardcoded Credentials category and impacts confidentiality, integrity, and availability of affected industrial systems.

Critical Impact
Network-reachable attackers can authenticate using undocumented built-in credentials and fully compromise SIMATIC CN 4100 devices without user interaction.

Affected Products

Siemens SIMATIC CN 4100 (hardware appliance)
Siemens SIMATIC CN 4100 firmware, all versions prior to V3.0
Operational technology environments running these devices on plant or enterprise networks

Discovery Timeline

2024-05-14 - CVE-2024-32740 published to NVD and Siemens advisory SSA-273900 released
2025-08-20 - Last updated in NVD database

Technical Details for CVE-2024-32740

Vulnerability Analysis

The SIMATIC CN 4100 firmware contains undocumented user accounts whose credentials are embedded in the shipped image. These accounts are not described in product documentation and cannot be removed or rotated by end users through normal administrative interfaces. Because the credentials are static across deployments, knowledge of a single set permits authentication against any unpatched device in the field.

The attack requires no privileges and no user interaction. The exposure is network-accessible, so any service the device exposes for management or remote control becomes a valid entry point. Successful authentication yields full read, write, and operational control of the device, including its role in industrial communication paths.

Root Cause

The root cause is the inclusion of undocumented accounts with embedded credentials in the firmware build, classified under [CWE-798] Use of Hard-coded Credentials. Vendors often introduce such accounts for manufacturing, support, or recovery workflows and fail to disable or rotate them before release. Once the firmware ships, the credentials become a shared secret across the installed base.

Attack Vector

An attacker reaches the device over any exposed management interface, supplies the undocumented credentials, and gains an authenticated session. From there the attacker can modify configuration, intercept or alter communication handled by the SIMATIC CN 4100, deploy persistent changes, or pivot deeper into the operational technology network. No verified public proof-of-concept exploit is listed in Exploit-DB, and the vulnerability is not present in the CISA Known Exploited Vulnerabilities catalog. Technical specifics on the accounts themselves are intentionally withheld in the Siemens Security Advisory SSA-273900.

Detection Methods for CVE-2024-32740

Indicators of Compromise

Successful logins to SIMATIC CN 4100 management services using account names that are not part of the documented user list
Configuration changes, firmware operations, or session activity occurring outside approved maintenance windows
Unexpected outbound connections initiated by the device to hosts outside the OT enclave

Detection Strategies

Inventory all SIMATIC CN 4100 units and confirm the running firmware version against the V3.0 patch baseline
Capture and review authentication logs from each device, flagging any usernames not provisioned by the operator
Correlate device telemetry with network flow records to identify management sessions originating from unauthorized subnets
Use a unified data lake such as Singularity Data Lake to centralize OT authentication and network logs for cross-source correlation

Monitoring Recommendations

Forward device syslog and authentication events to a SIEM and alert on logins outside expected administrator accounts
Monitor north-south and east-west traffic to the management interfaces of SIMATIC CN 4100 devices for new source addresses
Establish a behavioral baseline for the device and alert on deviations such as configuration writes, reboots, or new service bindings

How to Mitigate CVE-2024-32740

Immediate Actions Required

Upgrade SIMATIC CN 4100 firmware to V3.0 or later as directed in Siemens advisory SSA-273900
Restrict management interface access to a dedicated, isolated administrative VLAN with strict allowlists
Audit recent authentication and configuration logs on each device for signs of prior misuse
Block direct internet exposure of any SIMATIC CN 4100 management service at the perimeter firewall

Patch Information

Siemens has published fixed firmware in version V3.0 and later. Refer to the Siemens Security Advisory SSA-273900 for download instructions, signature verification, and upgrade procedures specific to the SIMATIC CN 4100 platform.

Workarounds

Place affected devices behind a firewall that permits only required protocols from defined engineering workstations
Apply Siemens' general operational guidelines for industrial security, including network segmentation and zone-and-conduit design per IEC 62443
Disable any unused management services on the device to reduce the attack surface until firmware can be updated
Use jump hosts with strong authentication and session recording for all administrative access to the device

bash

# Configuration example: restrict management access at the network boundary
# Replace placeholders with the addresses used in your environment

# Allow only the engineering workstation subnet to reach the device
iptables -A FORWARD -s 10.20.30.0/24 -d 10.50.0.10 -p tcp --dport 443 -j ACCEPT
iptables -A FORWARD -d 10.50.0.10 -j DROP

# Log any attempted access from unauthorized sources
iptables -A FORWARD -d 10.50.0.10 -j LOG --log-prefix "SIMATIC-CN4100-DENY: "