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Siemens SIMATIC S7-400 CPU (Update A)

Monitor7.5ICS-CERT ICSA-18-137-03May 15, 2018
Attack VectorNetwork
Auth RequiredNone
ComplexityLow
User InteractionNone needed
Summary

SIMATIC S7-400 CPU devices fail to properly validate incoming network packets (CWE-20), allowing an unauthenticated remote attacker to cause a denial of service by crashing or hanging the PLC. The vulnerability affects all versions of the standard S7-400 and S7-400H CPU hardware. For older hardware (v4.0 and earlier), Siemens has not released a firmware patch and requires a hardware upgrade to v5.0 or newer for S7-400, or v6.0 or newer for S7-400H. For S7-400 hardware v5.0, a firmware update to v5.2 or later is available. Users unable to upgrade should implement network segmentation, VPN protection for inter-cell communication, and firewall-based access controls to reduce exposure.

What this means
What could happen
An attacker with network access to a SIMATIC S7-400 CPU can trigger a denial of service condition, causing the PLC to stop responding and interrupting industrial processes until the device is manually restarted.
Who's at risk
Water authorities and electric utilities operating SIMATIC S7-400 PLCs for process automation, pump control, turbine management, and critical infrastructure operations. The affected hardware spans older v4.0 and v5.0 systems as well as redundant S7-400H units used in high-availability deployments.
How it could be exploited
An attacker sends specially crafted network packets to the S7-400 CPU. The device fails to properly validate the input, leading to a crash or hang that stops the PLC from processing control logic. No special credentials or complex setup is required—the attack works over the network if the CPU is reachable.
Prerequisites
  • Network access to the SIMATIC S7-400 CPU port (S7 protocol, typically port 102)
  • No authentication credentials required
  • Device must be directly reachable from attacker's network (Internet exposure increases risk significantly)
remotely exploitableno authentication requiredlow complexityaffects critical control logic executionolder hardware lacks vendor fix (end-of-life)
Exploitability
Low exploit probability (EPSS 0.5%)
Affected products (3)
3 pending
ProductAffected VersionsFix Status
SIMATIC S7-400 CPU hardwareAll versionsNo fix yet
SIMATIC S7-400 CPU hardware<firmware V5.2No fix yet
SIMATIC S7-400 H CPU hardwareAll versionsNo fix yet
Remediation & Mitigation
0/6
Do now
0/1
HARDENINGApply Defense-in-Depth strategy: place S7-400 CPU behind firewalls, restrict network access to authorized engineering stations only, and isolate from business network.
Schedule — requires maintenance window
0/3

Patching may require device reboot — plan for process interruption

HOTFIXSIMATIC S7-400 (standard or F variant) with hardware versions v4.0 or older: Upgrade to hardware v5.0 or newer.
HOTFIXSIMATIC S7-400 (standard or F variant) with hardware v5.0: Update firmware to v5.2 or newer.
HOTFIXSIMATIC S7-400H CPU with hardware versions prior to v4.5: Upgrade to hardware v6.0 or newer.
Long-term hardening
0/2
HARDENINGImplement cell protection concept: segment the PLC network into isolated cells with restricted data flow between them.
HARDENINGUse VPN to encrypt and protect network communication between network cells and remote access points.
View full CISA ICS-CERT advisory
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Siemens SIMATIC S7-400 CPU (Update A) | CVSS 7.5 - OTPulse