CVE-2021-31894 in SIMATIC PCS 7
Summary
by MITRE • 07/13/2021
A vulnerability has been identified in SIMATIC PCS 7 V8.2 and earlier (All versions), SIMATIC PCS 7 V9.X (All versions), SIMATIC PDM (All versions), SIMATIC STEP 7 V5.X (All versions < V5.7), SINAMICS STARTER (containing STEP 7 OEM version) (All versions). A directory containing metafiles relevant to devices' configurations has write permissions. An attacker could leverage this vulnerability by changing the content of certain metafiles and subsequently manipulate parameters or behavior of devices that would be later configured by the affected software.
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Analysis
by VulDB Data Team • 07/16/2021
This vulnerability resides within several Siemens industrial automation products including SIMATIC PCS 7, SIMATIC PDM, and SIMATIC STEP 7 software suites. The core issue involves improper access control mechanisms where directory structures containing device configuration metafiles are configured with write permissions that should be restricted. This represents a classic privilege escalation flaw that aligns with CWE-276, specifically concerning incorrect permissions for critical resources. The vulnerability affects multiple generations of Siemens automation software spanning from PCS 7 V8.2 and earlier through various versions of PDM and STEP 7, creating a widespread impact across industrial control systems. The flaw manifests when metafiles that store device configuration parameters are stored in directories accessible to unauthorized users or processes with insufficient privileges.
The technical exploitation of this vulnerability enables an attacker to modify critical configuration metafiles that influence how industrial devices operate during subsequent configuration processes. When affected software reads these altered metafiles during device setup or parameter configuration, it processes the malicious content, potentially leading to unauthorized device behavior modification. This represents a sophisticated attack vector that leverages the principle of least privilege violation, where the system trusts configuration data without proper validation or access control enforcement. The vulnerability operates at the configuration management layer, making it particularly dangerous as it can affect device behavior during normal operations rather than just during specific configuration phases. This type of attack pattern corresponds to ATT&CK technique T1546.001, which involves modifying system level files to achieve persistence or execute malicious code.
The operational impact of this vulnerability extends beyond simple configuration manipulation to potentially compromise entire industrial control processes. When an attacker successfully modifies device parameters through these metafiles, they can alter process control behaviors, modify safety parameters, or even cause operational disruptions that affect production quality and safety. The vulnerability creates a persistent threat since once the metafiles are modified, the malicious configuration remains active until manually corrected. This risk is particularly severe in industrial environments where configuration changes can directly impact physical processes, equipment operation, and overall plant safety. The attack surface includes not only direct system access but also potential supply chain compromise scenarios where third-party tools or network access could provide attackers with the necessary privileges to modify these directories.
Mitigation strategies must focus on implementing proper access control measures including restricting write permissions on configuration directories and metafile locations. Organizations should enforce principle of least privilege principles across all industrial automation systems, ensuring that only authorized personnel with appropriate clearance can modify critical configuration files. Network segmentation and access control lists should be implemented to prevent unauthorized network access to these systems. Regular security assessments should include verification of file permissions and directory access controls as part of configuration management reviews. System administrators should implement file integrity monitoring solutions that can detect unauthorized modifications to critical configuration files. The vulnerability also highlights the importance of secure configuration management practices, including regular audits of access controls and proper change management procedures. Additionally, organizations should consider implementing application whitelisting controls to prevent unauthorized execution of configuration tools that might be used to exploit this vulnerability. The remediation approach should include both immediate access control fixes and long-term security hardening of industrial control system environments to prevent similar privilege escalation scenarios.