CVE-2011-20001 in SIMATIC S7-1200 CPU V1 family
Summary
by MITRE • 10/14/2025
A vulnerability has been identified in SIMATIC S7-1200 CPU V1 family (incl. SIPLUS variants) (All versions < V2.0.3), SIMATIC S7-1200 CPU V2 family (incl. SIPLUS variants) (All versions < V2.0.3). The web server interface of affected devices improperly processes incoming malformed HTTP traffic at high rate. This could allow an unauthenticated remote attacker to force the device entering the stop/defect state, thus creating a denial of service condition.
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Analysis
by VulDB Data Team • 10/14/2025
The vulnerability CVE-2011-20001 affects Siemens SIMATIC S7-1200 programmable logic controllers across multiple CPU families including SIPLUS variants, specifically impacting all versions prior to V2.0.3. This issue resides within the web server interface component of these industrial control devices, representing a critical security flaw that undermines the operational integrity of industrial automation systems. The vulnerability demonstrates characteristics consistent with a denial of service attack vector that can be exploited remotely without authentication requirements, making it particularly dangerous in industrial environments where continuous operation is paramount. The affected devices operate within critical infrastructure sectors including manufacturing, process control, and industrial automation where device availability directly impacts production continuity and safety protocols.
The technical flaw manifests through improper handling of malformed HTTP traffic when processed at high rates by the web server interface component. This processing error occurs at the application layer of the network stack, specifically within the HTTP protocol handling mechanisms of the embedded web server. The vulnerability stems from inadequate input validation and error handling procedures that fail to properly sanitize or reject malformed HTTP requests. When subjected to rapid succession of malformed HTTP traffic, the device's web server component becomes overwhelmed and enters a stop or defect state, effectively rendering the controller inoperable. This behavior aligns with CWE-129 Input Validation and Output Encoding, specifically addressing improper validation of input data that leads to system instability. The flaw represents a classic example of resource exhaustion or state corruption vulnerability that can be amplified through rate-based attacks.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise industrial control processes that depend on continuous PLC operation. When affected controllers enter a stop/defect state, production lines may halt unexpectedly, leading to significant financial losses and potential safety hazards in process control environments. The remote nature of the attack means that adversaries can exploit this vulnerability from external networks without requiring physical access to the industrial facility, making it particularly concerning for operational technology environments. This vulnerability can be classified under the MITRE ATT&CK framework as a Denial of Service technique, specifically targeting the availability aspect of the CIA triad. The attack can be executed through network-based means, potentially leveraging tools or automated scripts to flood the device with malformed HTTP requests, causing the system to become unresponsive and requiring manual intervention or power cycling to restore normal operation.
Mitigation strategies for CVE-2011-20001 should focus on immediate firmware upgrades to versions V2.0.3 or later, which contain patches addressing the HTTP processing flaws. Network segmentation and access control measures should be implemented to restrict unauthorized access to the web interfaces of these devices, particularly through the use of firewalls and network access control lists that limit exposure to only authorized personnel. Additional protective measures include implementing network monitoring to detect unusual HTTP traffic patterns that may indicate exploitation attempts, and establishing robust change management procedures to ensure timely deployment of security updates. Organizations should also consider disabling unnecessary web server interfaces on industrial controllers when not required for operational purposes, reducing the attack surface. The vulnerability highlights the importance of maintaining up-to-date industrial control system firmware and implementing proper security practices for operational technology environments, as these systems often operate in isolated networks where security updates may be delayed or overlooked. Regular vulnerability assessments and penetration testing of industrial control systems should be conducted to identify similar weaknesses in other components of the operational technology infrastructure.