Critical Fortinet Vulnerabilities Expose Siemens RUGGEDCOM Devices to Remote Takeover

In the complex world of Operational Technology (OT), the convergence of IT and industrial hardware creates unique security challenges. A recent advisory highlights a perfect storm of these risks: critical vulnerabilities in Siemens RUGGEDCOM APE1808 devices stemming from underlying flaws in Fortinet’s FortiOS. For organizations managing Critical Infrastructure—specifically in Energy, Transportation, and Manufacturing—this is not just a software bug; it is a potential gateway for attackers to manipulate physical environments.

At Security Arsenal, we are tracking this situation closely because of the severity of the involved CVEs, particularly one allowing unauthenticated remote code execution. Here is our deep dive into the threat landscape and how you can defend your industrial control systems (ICS).

The Threat Landscape: When Hardware Inherits Software Flaws

The Siemens RUGGEDCOM APE1808 is a robust device designed for harsh environments, commonly found in substations and transportation networks. However, these devices rely on Fortinet FortiOS to handle networking and security functions. This advisory reveals that four distinct vulnerabilities in FortIOS affect the RUGGEDCOM APE1808, creating a multi-vector attack surface.

The Vulnerabilities

Siemens has confirmed that all versions of the RUGGEDCOM APE1808 are currently affected. The vulnerabilities range from Medium to Critical severity:

CVE-2026-24858 (CVSS 9.8 - CRITICAL): This is the most alarming flaw. It is an Authentication Bypass using an Alternate Path or Channel (CWE-288). If FortiCloud SSO is enabled, an attacker with a valid FortiCloud account and a registered device could potentially log into other devices registered to different accounts. In an ICS environment, this effectively obliterates the perimeter, allowing unauthorized access to sensitive management interfaces.
CVE-2025-55018 (CVSS 5.8 - MEDIUM): This vulnerability involves HTTP Request Smuggling (CWE-444). An attacker can send a specially crafted header to smuggle an unlogged HTTP request through firewall policies. This is particularly insidious for security monitoring, as it allows malicious traffic to bypass logging and detection mechanisms.
CVE-2025-64157 (CVSS 6.7 - MEDIUM): A Use of Externally-Controlled Format String vulnerability (CWE-134) that allows an authenticated admin to execute unauthorized code or commands via a crafted configuration. While it requires authentication, the combination with the auth bypass (CVE-2026-24858) makes this highly exploitable.
CVE-2025-62439 (CVSS 4.2 - MEDIUM): Involves Improper Verification of the Source of a Communication Channel (CWE-940).

Impact on Critical Infrastructure

The RUGGEDCOM series is a staple in environments where uptime is non-negotiable. A Critical severity score of 9.8 implies that these vulnerabilities are remotely exploitable, require low complexity to attack, and need no privileges. If an attacker leverages the authentication bypass, they could gain administrative control over devices that bridge the gap between corporate IT and operational OT networks.

Detection and Threat Hunting

Identifying exploitation of these vulnerabilities requires a two-pronged approach: verifying patch compliance and hunting for suspicious network activity.

1. Hunt for HTTP Request Smuggling (CVE-2025-55018)

Detecting HTTP smuggling often requires analyzing raw request logs. Attackers manipulate headers like Content-Length and Transfer-Encoding. Use the following KQL query in Microsoft Sentinel or Defender to flag potential smuggling attempts where both headers are present or mismatched significantly.

Script / Code

DeviceNetworkEvents
| where ActionType has "HttpRequest"
| where isnotempty(RequestHeader) and isnotempty(AdditionalFields)
| parse RequestHeader with * 'Content-Length:' ContentLength:string * 'Transfer-Encoding:' TransferEncoding:string *
| where isnotempty(ContentLength) and isnotempty(TransferEncoding)
| project Timestamp, DeviceName, SourceIP, DestinationIP, RequestHeader, ContentLength, TransferEncoding
| extend SmugglingScore = iff(toint(ContentLength) > 0 and TransferEncoding contains "chunked", "High", "Medium")
| sort by Timestamp desc

2. Asset Verification

Security teams should immediately scan their environments for affected Siemens hardware. While standard IP scanners are useful, querying the device management interface via SNMP can provide specific version information if the community string is known or discovered internally.

Script / Code

#!/bin/bash
# Simple SNMP check for RUGGEDCOM APE1808 devices
# Requires snmpwalk and the specific OID for sysDescr or product version

TARGET_IP=$1
COMMUNITY="public"

if [ -z "$TARGET_IP" ]; then
  echo "Usage: $0 <target_ip>"
  exit 1
fi

echo "Scanning $TARGET_IP for Siemens RUGGEDCOM info..."

# Query system description to identify device model
snmpwalk -v 2c -c $COMMUNITY $TARGET_IP sysDescr.0

# Note: Confirm exact OIDs for firmware version in Siemens MIBs for accurate patching status.

Mitigation Strategy

Siemens has released a new version specifically to address these issues. Given the Critical rating of CVE-2026-24858, patching should be treated as an emergency.

1. Immediate Firmware Updates Siemens advises updating to the latest version of the RUGGEDCOM APE1808 firmware immediately. Since the underlying issue is FortiOS-based, ensure that the update includes the fixes for FortiOS v7.4.10/7.4.11 or later, depending on the specific component (FortiGate NGFW or FortiManager).

2. Review FortiCloud SSO Configuration Until patches are fully deployed, review if FortiCloud SSO is strictly necessary. If it can be disabled, it temporarily removes the attack vector for the authentication bypass.

3. Network Segmentation and Isolation As per CISA recommendations:

Minimize network exposure for all control system devices. Ensure they are not accessible from the internet.
Locate control system networks and remote devices behind firewalls and isolate them from the business network.

4. Deep Packet Inspection Ensure your perimeter firewalls are inspecting HTTP traffic strictly to identify malformed headers indicative of smuggling attempts.

Conclusion

The reliance on common operating systems like FortiOS in specialized industrial hardware creates a supply chain risk that requires constant vigilance. For Security Arsenal clients, we recommend prioritizing this patch cycle above standard IT updates due to the Critical Infrastructure impact.

Related Resources

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