CVE-2024-31853 Overview
CVE-2024-31853 affects Siemens SICAM TOOLBOX II in all versions prior to V07.11. The application establishes HTTPS connections to managed device TLS servers without validating the Extended Key Usage (EKU) attribute on the presented certificate. This certificate validation gap [CWE-295] allows an on-path attacker to impersonate managed devices and intercept communications between the engineering tool and the substation equipment it manages.
Critical Impact
An attacker positioned between SICAM TOOLBOX II and a managed device can execute a machine-in-the-middle (MitM) attack, compromising the confidentiality and integrity of engineering communications with energy automation hardware.
Affected Products
- Siemens SICAM TOOLBOX II — all versions prior to V07.11
- Engineering workstations running vulnerable SICAM TOOLBOX II builds
- Substation automation environments managed via the affected toolbox
Discovery Timeline
- 2025-07-08 - CVE-2024-31853 published to the National Vulnerability Database
- 2025-08-20 - Last updated in NVD database
- Vendor advisory - Siemens Security Advisory SSA-183963
Technical Details for CVE-2024-31853
Vulnerability Analysis
The flaw resides in the TLS client logic of SICAM TOOLBOX II. When the application opens an HTTPS session with a managed device, it validates the certificate chain but skips inspection of the Extended Key Usage extension. The EKU extension constrains what purposes a certificate may be used for, such as serverAuth or clientAuth. Without this check, any certificate trusted by the application — including certificates issued for unrelated purposes — can be presented by an impostor server.
An attacker on the network path between the engineering workstation and the managed device can terminate the TLS session using such a certificate. The toolbox accepts the connection and proceeds to exchange engineering data, configuration commands, and credentials with the attacker-controlled endpoint. This category of weakness is tracked as Improper Certificate Validation [CWE-295].
Root Cause
The TLS validation routine in SICAM TOOLBOX II does not enforce that the device certificate carries an EKU value appropriate for TLS server authentication. The vendor introduced enforcement of this check in version V07.11.
Attack Vector
Exploitation requires network adjacency and user interaction. The attacker must be positioned on the path between the toolbox and the target device, for example through ARP spoofing, rogue gateway placement, or a compromised network device in the substation LAN. The operator must then initiate an HTTPS session to the managed device. No authentication is required on the attacker side because the toolbox itself accepts the malicious certificate.
The vulnerability mechanism is described in the Siemens Security Advisory SSA-183963. No public proof-of-concept exploit is currently available, and the EPSS score sits at 0.173%.
Detection Methods for CVE-2024-31853
Indicators of Compromise
- Unexpected TLS certificates presented by managed devices, particularly certificates lacking a serverAuth EKU or carrying unrelated EKU values.
- TLS sessions from SICAM TOOLBOX II hosts terminating at IP addresses that do not match the inventoried management plane of the substation.
- ARP table anomalies, duplicate MAC addresses, or gateway changes on the engineering VLAN preceding toolbox sessions.
Detection Strategies
- Capture and inspect TLS handshakes from engineering workstations and alert on certificates missing a valid id-kp-serverAuth EKU.
- Maintain a baseline inventory of legitimate device certificates and flag deviations in issuer, subject, or fingerprint during toolbox sessions.
- Correlate Layer 2 anomalies on the OT network with HTTPS session initiation from SICAM TOOLBOX II hosts.
Monitoring Recommendations
- Forward engineering workstation network telemetry and TLS metadata into a centralized analytics platform for retention and review.
- Monitor SICAM TOOLBOX II host versions across the fleet and alert when versions below V07.11 are observed.
- Track outbound connections from engineering hosts to ensure they terminate only at sanctioned device IP ranges.
How to Mitigate CVE-2024-31853
Immediate Actions Required
- Upgrade SICAM TOOLBOX II to version V07.11 or later on every engineering workstation that connects to managed devices.
- Restrict the engineering network so that only authorized workstations can reach the management interfaces of SICAM devices.
- Audit certificates installed on managed devices and reissue any that lack a proper serverAuth EKU value.
Patch Information
Siemens addressed the issue in SICAM TOOLBOX II V07.11. Refer to Siemens Security Advisory SSA-183963 for the official fix bulletin and download instructions.
Workarounds
- Segment the OT engineering network using dedicated VLANs and firewall rules to reduce the opportunity for on-path positioning.
- Enforce static ARP entries or use network access control on the engineering VLAN to limit ARP spoofing risk.
- Perform engineering sessions only from trusted, hardened workstations connected directly to known-good management segments.
# Configuration example - verify installed SICAM TOOLBOX II version on Windows
wmic product where "Name like 'SICAM TOOLBOX II%%'" get Name,Version
# Inspect a managed device certificate and confirm Extended Key Usage
openssl s_client -connect <device_ip>:443 -showcerts </dev/null \
| openssl x509 -noout -text \
| grep -A1 "Extended Key Usage"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
