CVE-2025-39844: Multiple Memory Corruption Flaws in Siemens SIMATIC CN 4100 Threaten Communication Node Availability

Executive Summary

CVE-2025-39844 bundles multiple memory corruption defects in the Siemens SIMATIC CN 4100 communication node, including NULL pointer dereference, reachable assertion, use-after-free, and out-of-bounds write conditions that an attacker can trigger to degrade or crash the device. Because the CN 4100 sits in the communication path between control segments and higher-level networks, a successful trigger can sever process visibility and disrupt the data flows that operators depend on for safe control.

Technical Exposure Breakdown

The SIMATIC CN 4100 is a communication node designed to bridge industrial network segments, and the vulnerability class described here is memory corruption in the device firmware. The vendor advisory carries a v3 base score of 9.6 in the equipment context, while the tracked score for this specific identifier sits at 7.5. That gap matters. The 9.6 reflects the worst-case chaining of the full defect set, and OT engineers should plan against the higher number rather than the lower.

The four defect types have different exploitation profiles. A NULL pointer dereference and a reachable assertion typically resolve to a denial-of-service outcome, meaning the device faults or halts when it processes malformed input. A use-after-free and an out-of-bounds write are more serious. Both can, under the right conditions, allow an attacker to corrupt device memory in a controlled manner, which opens the door to code execution and therefore to integrity and confidentiality loss rather than just availability loss.

The attack vector is the network interface. Any host that can reach the CN 4100 management or data plane over the affected protocol path can attempt to deliver crafted packets. In practice this means the exposure is bounded by your network segmentation. A CN 4100 reachable only from a tightly controlled control segment is a materially different risk than one reachable from a shared plant network or an engineering VLAN with loose access.

OT Impact and Compliance Risk

The physical consequence is loss of communication continuity. If the CN 4100 crashes, the segments it bridges lose their path to each other. That can blind SCADA and HMI systems to live process state, delay or drop control commands, and force operators into manual fallback if the affected node carries safety-relevant or supervisory traffic. A memory corruption that escalates to code execution is worse still, because it converts a communication device into an attacker foothold inside the OT trust boundary.

For IEC 62443 environments, this defect undermines zone and conduit assumptions if the CN 4100 is a conduit device. A compromised conduit breaks the segmentation model that many risk assessments rely on. NERC CIP registered entities should treat the node as a candidate BES Cyber Asset or Protected Cyber Asset depending on its role and document the exposure under CIP-007 patch management and CIP-010 configuration baselines. Pipeline operators under TSA SD-02C should map this against their required network segmentation and access control measures, since the flaw directly targets a segmentation-relevant device. Water and wastewater utilities under AWIA 2018 should fold it into their risk and resilience assessment where SIMATIC communication nodes carry process data.

Compensating Controls

Do not rely on active scanning to confirm exposure. Probing a memory-corruption-prone communication node with unvalidated traffic can trigger the exact fault you are trying to prevent, and active scanning has bricked industrial components before. Confirm asset presence through passive traffic analysis and configuration inventory instead.

Immediate compensating controls should focus on reachability. Restrict the CN 4100 management and data plane to a defined allowlist of engineering hosts using firewall or ACL enforcement at the conduit boundary. Where the node bridges segments, verify that no path exists from IT or shared infrastructure to the device without traversing a controlled chokepoint.

A virtual patch approach fits well here because the trigger is malformed network input. Deploy an IDS or IPS inline or in monitor mode at the conduit and build a Suricata rule concept that alerts on anomalous packet sizes and malformed field structures directed at the CN 4100 ports, treating oversized or truncated payloads to the device as high-priority events. Pair this with alerting on unexpected source addresses talking to the node, since a legitimate CN 4100 conversation set is small and predictable. Schedule the vendor firmware update to version 5.0 or later during a planned maintenance window once you have validated it in a staging environment.

BreachSpider Intel Footer

BreachSpider tracks CVE-2025-39844 and the wider SIMATIC exposure surface across our database of 25,000+ ICS CVEs and 175,000+ OT products for continuous monitoring of your asset base.