CVE-2014-2256 in SIMATIC S7 Cpu-1211c
Summary
by MITRE
Siemens SIMATIC S7-1200 CPU PLC devices with firmware before 4.0 allow remote attackers to cause a denial of service (defect-mode transition) via crafted ISO-TSAP packets, a different vulnerability than CVE-2014-2257.
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Analysis
by VulDB Data Team • 05/08/2026
The vulnerability identified as CVE-2014-2256 affects Siemens SIMATIC S7-1200 CPU programmable logic controllers where firmware versions prior to 4.0 are susceptible to remote denial of service attacks through the manipulation of ISO-TSAP packets. This flaw represents a critical security weakness in industrial control systems that can lead to operational disruption and potential safety hazards in manufacturing environments. The vulnerability specifically targets the communication protocols used in industrial automation systems, where reliable operation is paramount for continuous production processes. The affected devices operate within the broader context of industrial control systems that are increasingly connected to corporate networks, creating expanded attack surfaces that require careful security consideration.
The technical implementation of this vulnerability stems from insufficient validation of ISO-TSAP (ISO Transport Service Access Point) packets received by the S7-1200 CPU devices. ISO-TSAP is a standard protocol layer that provides connection-oriented communication services in the OSI model, and when improperly handled, can lead to unexpected device behavior. Attackers can craft malicious packets that exploit weaknesses in the packet processing logic, causing the PLC to enter an unintended defect mode. This defect mode transition represents a state where the device becomes unresponsive or enters a non-operational state, effectively rendering the industrial process controlled by that device unavailable. The vulnerability is classified under CWE-248, which addresses exposure of an uninitialized variable, though the specific manifestation in this case involves improper packet handling rather than simple variable initialization issues.
The operational impact of CVE-2014-2256 extends beyond simple service disruption, as industrial control systems depend on continuous operation for safety and production purposes. When a PLC enters defect mode, it can cause cascading failures throughout the manufacturing process, potentially leading to equipment damage, production downtime, and safety risks. The remote nature of the attack means that threat actors can exploit this vulnerability from outside the operational technology network, making traditional perimeter-based security measures insufficient. This vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks targeting industrial control systems, and demonstrates how attackers can leverage protocol weaknesses to compromise operational integrity. The affected environment typically includes process control systems where the S7-1200 PLCs are deployed as part of larger automation networks that may also contain other Siemens devices and potentially legacy systems.
Mitigation strategies for this vulnerability primarily involve firmware updates to version 4.0 or later, which contain patches addressing the packet validation issues. Organizations should also implement network segmentation to isolate critical industrial control systems from general corporate networks, reducing the attack surface available to remote threat actors. Network monitoring and intrusion detection systems should be configured to identify anomalous ISO-TSAP traffic patterns that may indicate exploitation attempts. Additionally, implementing proper access controls and authentication mechanisms for PLC communication can help prevent unauthorized access to these critical devices. The remediation process requires careful planning to avoid disrupting ongoing production processes, and should include thorough testing of updated firmware in controlled environments before deployment to production systems. Security teams should also consider the broader context of industrial cybersecurity frameworks such as NIST SP 800-82 and IEC 62443 standards, which provide guidance for protecting industrial control systems from similar vulnerabilities.