Full Report
Affected models of the S7-1500 CPU product family do not contain an Immutable Root of Trust in Hardware. With this the integrity of the code executed on the device can not be validated during load-time. An attacker with physical access to the device could use this to replace the boot image of the device and execute arbitrary code. As exploiting this vulnerability requires physical tampering with the product, Siemens recommends to assess the risk of physical access to the device in the target deployment and to implement measures to make sure that only trusted personnel have access to the physical hardware. The vulnerability is related to the hardware of the product. Siemens has released new hardware versions for several CPU types of the S7-1500 product family in which this vulnerability is fixed and is working on new hardware versions for remaining PLC types to address this vulnerability completely. See the chapter “Additional Information” below for more details. For more information please also refer to the related product support article: https://support.industry.siemens.com/cs/ww/en/view/109816536/.
Analysis Summary
# Vulnerability: Missing Immutable Root of Trust in Siemens S7-1500 CPUs
## CVE Details
- **CVE ID:** CVE-2022-38773 (Assigned to this specific hardware flaw in the S7-1500 family)
- **CVSS Score:** 6.8 (Medium)
- **CWE:** CWE-1327: Binding to Non-Bindable Entities; CWE-453: Damage to System Isolation (related to lack of hardware-enforced integrity)
## Affected Systems
- **Products:** Siemens SIMATIC S7-1500 CPU product family.
- **Versions:** All hardware versions (generations) preceding the latest hardware release (specifically those without the updated secure boot architecture).
- **Configurations:** Devices deployed in environments where physical access to the PLC hardware is possible.
## Vulnerability Description
Affected S7-1500 CPUs lack an **Immutable Root of Trust** within the hardware. This architectural deficiency prevents the system from performing a secure boot process that validates the digital signature and integrity of the firmware/code during load-time. Consequently, the hardware cannot verify if the boot image has been altered by an unauthorized party.
## Exploitation
- **Status:** Not currently reported as exploited in the wild; however, the architectural flaw is well-documented in industrial security research.
- **Complexity:** High (Requires physical disassembly and specialized equipment to flash/replace the boot image).
- **Attack Vector:** Physical (The attacker must have hands-on access to the device).
## Impact
- **Confidentiality:** High (Potential to extract sensitive data or credentials from the device memory).
- **Integrity:** High (Attacker can execute arbitrary code and modify PLC logic/operating system).
- **Availability:** High (Attacker can render the device inoperable or alter industrial processes).
## Remediation
### Patches
- **Hardware Upgrade:** Because the flaw is rooted in the physical hardware architecture, it cannot be fixed via a software or firmware update.
- **New Hardware Versions:** Siemens has released **new hardware versions** for several CPU types within the S7-1500 family that include a hardware-based Root of Trust. Users must replace existing physical units with the new hardware versions to fully remediate the risk.
### Workarounds
- **Physical Security:** Implement strict access controls to the cabinets and areas where PLCs are housed. Use locks, tamper-evident seals, and surveillance.
- **Personnel Vetting:** Ensure only trusted and authorized personnel have physical access to the hardware.
- **Defense in Depth:** Utilize environmental monitoring to detect unauthorized access to control rooms or electrical enclosures.
## Detection
- **Indicators of Compromise:** Unexpected reboots, modified checksums (if detectable via external auditing tools), or deviations in PLC cycle times.
- **Detection methods and tools:** Regular physical inspections for signs of hardware tampering or unauthorized serial connections. Use of industrial IDS (Intrusion Detection Systems) to monitor for anomalous network behavior that might indicate compromised firmware is communicating externally.
## References
- **Siemens Security Advisory:** hXXps://cert-portal.siemens.com/productcert/pdf/ssa-482748.pdf
- **Siemens Product Support Article:** hXXps://support.industry.siemens.com/cs/ww/en/view/109816536/