Missing Immutable Root of Trust in S7-1500 CPU devices
Monitor4.6SSA-482757Jan 10, 2023
Attack VectorPhysical
Auth RequiredNone
ComplexityLow
User InteractionNone needed
Summary
The S7-1500 CPU product family lacks an immutable root of trust in hardware, meaning the integrity of boot code cannot be cryptographically verified during startup. An attacker with physical access to the device could replace the boot image and execute arbitrary code. The vulnerability is a hardware design limitation affecting all versions of SIMATIC Drive Controller CPU models and S7-1500 CPUs (including ET 200pro and SIPLUS variants). Siemens states that new hardware versions with the vulnerability fixed are available for some CPU types, with additional versions in development. Exploitation requires direct physical tampering with the device and is not remotely exploitable.
What this means
What could happen
An attacker with physical access to an S7-1500 CPU could replace the boot image and execute arbitrary code on the controller, potentially altering process logic or stopping production. Since no hardware fix is available for existing devices, this vulnerability is permanent unless the hardware is physically replaced with newer versions.
Who's at risk
Manufacturing and transportation facilities operating Siemens S7-1500 PLC CPU controllers (all models and firmware versions) are affected. This includes process automation, motion control, and safety-related applications running on SIMATIC Drive Controllers and S7-1500 CPUs in distributed I/O configurations (ET 200pro, ET 200SP) and rail-mounted variants. Any organization with physical control systems relying on these devices should assess their physical security posture.
How it could be exploited
An attacker with physical access to the CPU hardware would exploit the missing immutable root of trust by directly tampering with the device's boot image before startup. The attacker replaces the legitimate boot code with malicious code, which the CPU then executes without validation since it cannot cryptographically verify the integrity of the boot image at load time.
Prerequisites
- Physical access to the S7-1500 CPU device
- Ability to remove or modify the device's boot/firmware storage
- No physical tamper-evident seals or access controls in place
No patch availableRequires physical access to deviceAffects all S7-1500 CPU variants (hardware-level issue)No vendor fix planned for existing hardwareLow complexity exploitation once physical access is gained
Exploitability
Low exploit probability (EPSS 0.1%)
Affected products (71)
71 pending
ProductAffected VersionsFix Status
SIMATIC Drive Controller CPU 1504D TFAll versionsNo fix yet
SIMATIC Drive Controller CPU 1507D TFAll versionsNo fix yet
SIMATIC S7-1500 CPU 1510SP F-1 PNAll versionsNo fix yet
SIMATIC S7-1500 CPU 1510SP-1 PNAll versionsNo fix yet
SIMATIC S7-1500 CPU 1511-1 PNAll versionsNo fix yet
Remediation & Mitigation
0/4
Do now
0/2HARDENINGImplement physical access controls to the CPU: restrict entry to equipment rooms, use locked enclosures, and limit access to authorized maintenance personnel only
HARDENINGDeploy tamper-evident seals or tamper-detection mechanisms on CPU devices to alert if physical access has been attempted
Schedule — requires maintenance window
0/1Patching may require device reboot — plan for process interruption
HARDENINGEstablish a procedure for verifying CPU integrity after any maintenance or unplanned downtime
Long-term hardening
0/1HOTFIXPlan hardware replacement with new S7-1500 CPU versions that include immutable root of trust once available from Siemens
CVEs (1)
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