CVE-2021-31337 in SINAMICS SL150
Summary
by MITRE • 06/28/2021
The Telnet service of the SIMATIC HMI Comfort Panels system component in affected products does not require authentication, which may allow a remote attacker to gain access to the device if the service is enabled. Telnet is disabled by default on the SINAMICS Medium Voltage Products (SINAMICS SL150: All versions, SINAMICS SM150: All versions, SINAMICS SM150i: All versions).
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Analysis
by VulDB Data Team • 07/03/2021
The vulnerability identified as CVE-2021-31337 affects the SIMATIC HMI Comfort Panels system component within Siemens industrial automation products, specifically targeting the Telnet service implementation. This security weakness represents a critical authentication bypass flaw that exposes affected devices to unauthorized remote access attempts. The vulnerability is particularly concerning within industrial control systems where operational technology environments require robust security measures to prevent unauthorized access to critical infrastructure components. The affected products include various SIMATIC HMI Comfort Panels that utilize the Telnet protocol for administrative access, creating a potential attack vector for malicious actors targeting industrial control systems.
The technical flaw stems from the Telnet service implementation that fails to enforce proper authentication mechanisms, allowing any remote attacker to establish connections without valid credentials. This design deficiency violates fundamental security principles and creates an inherently insecure access point within the industrial control environment. The vulnerability exists because the Telnet service operates without requiring authentication, meaning that any network-connected attacker who can reach the device can potentially gain administrative access. This authentication bypass directly maps to CWE-287, which addresses improper authentication issues in software systems. The flaw demonstrates poor security architecture where the service should have implemented proper authentication controls but instead provides open access to system functions.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it can lead to complete system compromise within industrial environments. Remote attackers can exploit this weakness to execute arbitrary commands, modify system configurations, access sensitive operational data, and potentially disrupt critical manufacturing processes. The attack surface is particularly dangerous in industrial settings where HMI panels serve as primary interfaces for operator interaction and system monitoring. This vulnerability enables attackers to gain persistent access to industrial control systems, potentially leading to production disruptions, data manipulation, or even physical safety risks in critical infrastructure environments. The risk is amplified by the fact that Telnet is often enabled in production environments for administrative purposes, making the attack vector readily available to threat actors.
Organizations should implement immediate mitigations to address this vulnerability, including disabling the Telnet service on affected devices and replacing it with secure alternatives such as SSH protocols. The recommended approach involves configuring the affected SIMATIC HMI Comfort Panels to disable Telnet access entirely and enforce secure remote access methods. Security administrators should also implement network segmentation to isolate industrial control systems from general network access, reducing the attack surface for potential exploitation attempts. Additional protective measures include deploying network access controls, implementing intrusion detection systems, and establishing regular security assessments to identify and remediate similar vulnerabilities. The mitigation strategy aligns with ATT&CK technique T1021.004 for remote service access and emphasizes the importance of proper access control implementation. Organizations should also consider implementing zero-trust network architectures that enforce strict authentication requirements for all system access attempts, particularly in industrial environments where operational technology security is paramount.