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Independent researchers Gleb Gritsai, Alexander Zaitsev, Sergey Scherbel, Yuri Goltsev, Dmitry Serebryannikov, Sergey Bobrov, Denis Baranov, Andrey Medov from Positive Technologies have identified multiple vulnerabilities in the Siemens WinCC application. In evaluating these reported vulnerabilities, Siemens identified an additional vulnerability that is included in this advisory. Siemens has produced an update that resolves all vulnerabilities except the buffer overflow in DiagAgent. DiagAgent is no longer supported, and this vulnerability can be mitigated by disabling the service. ICS-CERT has not tested this update. These vulnerabilities may be remotely exploited.
Siemens WinCC 7.0 SP3 web server and web applications are affected.
These vulnerabilities may allow an attacker to gain unauthorized access, read from, or write to files and settings on the target system.
Impact to individual organizations depends on many factors that are unique to each organization. ICS-CERT recommends that organizations evaluate the impact of these vulnerabilities based on their operational environment, architecture, and product implementation.
Siemens SIMATIC HMI is a software package used as an interface between the operator and the programmable logic controllers (PLCs) controlling the process. SIMATIC HMI performs the following tasks: process visualization, operator control of the process, alarm display, process value and alarm archiving, and machine parameter management. This software is used in many industries, including food and beverage, water and wastewater, oil and gas, and chemical.
WinCC web applications are susceptible to reflected cross-site scripting because they do not filter out characters when parsing URL parameters. Exploitation of this vulnerability may give an attacker authenticated access to WinCC web applications.
XML (XPATH Injection)2
Web applications do not filter out special characters when parsing URL parameters. An attacker may exploit this vulnerability to read or write settings on the system.
Web applications do not sanitize URL parameters. An authenticated attacker can read arbitrary files on the system.
The DiagAgent Web server is used for remote diagnostic purposes and is disabled by default. If the service is enabled, it does not sanitize user input correctly. Specially crafted input can crash the DiagAgent, disabling the remote diagnostic service.
A Web application accepts a parameter in a HTTP GET request and interprets it as a URL. The victim’s browser is then redirected to that URL.
If a victim clicks on a link that was prepared by an attacker, the victim’s browser could be redirected to a malicious Web site instead of the WinCC system.
These vulnerabilities can be remotely exploited.
Existence of Exploit
No known public exploits specifically target these vulnerabilities.
An attacker with a low skill would be able to exploit these vulnerabilities.
Siemens has released a security advisory.
Siemens has produced an update that resolves all vulnerabilities except the buffer overflow in DiagAgent. The buffer overflow was not fixed, because the vulnerable DiagAgent is turned off by default and is no longer distributed or supported. The update is available in Update 2 for WinCC V7.0 SP3. Siemens recommends applying this patch as soon as possible.
The Buffer Overflow vulnerability can only be exploited if the user starts the DiagAgent Web server manually. Siemens recommends that users check to ensure that the DiagAgent Web server is disabled and cautions users to only enable this option if and when it is needed.
ICS-CERT encourages asset owners to take additional defensive measures to protect against this and other cybersecurity risks.
- Minimize network exposure for all control system devices. Critical devices should not directly face the Internet.
- Locate control system networks and remote devices behind firewalls, and isolate them from the business network.
- When remote access is required, use secure methods, such as Virtual Private Networks (VPNs), recognizing that VPN is only as secure as the connected devices.
The Control Systems Security Program (CSSP) also provides a section for control systems security recommended practices on the CSSP Web page. Several recommended practices are available for reading and download, including Improving Industrial Control Systems Cybersecurity with Defense-in-Depth Strategies.
ICS-CERT reminds organizations to perform proper impact analysis and risk assessment prior to taking defensive measures.
Organizations observing any suspected malicious activity should follow their established internal procedures and report their findings to ICS-CERT for tracking and correlation against other incidents.
- 1CWE, http://cwe.mitre.org/data/definitions/79.html, Web site last accessed June 06, 2012.
- 2CWE-91: XML Injection, http://cwe.mitre.org/data/definitions/91.html, Web site last accessed June 06, 2012.
- 3CWE-22: Improper Limitation of a Pathname to a Restricted Directory, http://cwe.mitre.org/data/definitions/22.html, Web site last accessed June 06, 2012.
- 4CWE, http://cwe.mitre.org/data/definitions/79.html, Web site last accessed June 06, 2012.
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