DHS warns of another dangerous flaw in Advantech WebAccess SCADA software

The US DHS Industrial Control Systems CERT (ICS-CERT) has warned organizations using Advantech’s ICS products to install an update that kills a remotely exploitable flaw in its WebAccess software. 

WebAccess is the Taiwanese company’s browser-based SCADA software for monitoring remote field devices. It’s known among security researchers as a type of SCADA Human Machine Interface (HMI) system and has been the focus of security research in part because of its use of Microsoft’s implementation of distributed computing  protocol, Remote Procedure Call (RPC). 

A researcher at Trend Micro discovered multiple vulnerabilities in WebAccess, the worst of which is a stack-based bugger overflow, tracked as CVE-2018-14816, that has a CVSS version 3 score of 9.8 out of a possible 10. Another path traversal flaw that may allow an attacker to execute arbitrary code was given the same score, while others rated 7.5 and 7.8 scores.   

As ICS-CERT notes, WebAccess is used in critical manufacturing, energy, water, and wastewater systems in East Asia, the US, and Europe. 

“Successful exploitation of these vulnerabilities could allow an attacker to execute arbitrary code, access files and perform actions at a privileged level, or delete files on the system,” ICS-CERT warns in its risk assessment. 

Advantech has released version 8.3.3 of WebAccess to fix the remotely exploitable bugs, which ICS-CERT emphasized requires a “low skill level to exploit”. WebAccess Versions 8.3.1 and prior are affected, according to ICS-CERT.  

Advantech’s WebAccess 8.3.3 release is available here where it details security updates for WebAccess on Windows 10, Windows 7, and Windows Server 2012 R2 machines.  

Fortunately, ICS-CERT is not aware of any public exploits targeting these vulnerabilities.

However, the latest fix follows the March release of a public exploit from a Tenable Security researcher Chris Lyne for an unauthenticated remote code execution flaw that worked against WebAccess versions 8.3, despite Advantech’s January release of WebAccess version 8.3 supposedly having addressed CVE-2017–16720, the flaw the exploit utilized. 

Lyne in July discovered his exploit also worked against the subsequently released WebAccess versions 8.3.1 and 8.3.2. 

“According to the WebAccess Support & Download page, 8.3.2 was released on August 17, 2018. It appears there was never a patch for this vulnerability,” Lyne wrote in September. 

He also found dozens of internet-exposed WebAccess instances through the IoT search engine, Shodan.io, which were likely a fraction of all WebAccess installations worldwide. 

WebAccess has become testing ground for researchers looking for bugs in Remote Procedure Call (RPC) protocols, which were developed in the pre-internet era and later implemented in Windows. 

Trend Micro’s Zero Day Initiative (ZDI) revealed in January this year that around 2016 it had paid for a “trove of vulnerability reports” written previously by an anonymous researcher who’d been investigating vulnerabilities in WebAccess RPC interfaces.   

ZDI researcher Fritz Sands explained that WebAccess installation and setup opens ports 4592 and 14592 for TCP traffic, which use RPC protocols to communicate with clients.  

Microsoft’s RPC implementation allows Windows machines to talk with other RPC-enabled systems, such as those that use Open Group’s Distributed Computing Environment (DCE) for RPC.   

“These ports are serviced by processes (webvrpcs.exe and datacore.exe) that run in the context of a local administrator. These ports use Remote Procedure Call (RPC) protocols to communicate with clients, and both of the RPC interfaces can be called from remote unauthenticated clients,” he noted. 

Sands, who was credited with reporting WebAccess bugs that were fixed in May, noted that code in Advantech’s WebAccess version 8.0 software package “contains many exploitable vulnerabilities” and encouraged hackers to use it test newer versions of WebAccess and then explore other products that use RPC services.