Details and PoC for critical SharePoint RCE flaw released
Last week, a “wormable” remote code execution flaw in the Windows DNS Server service (CVE-2020-1350) temporarily overshadowed all the other flaws patched by Microsoft on July 2020 Patch Tuesday, but CVE-2020-1147, a RCE affecting Microsoft SharePoint, was also singled out as critical and requiring a speedy fix.
Implementing the offered security updates has since become even more urgent, as more exploitation details and a PoC have been released on Monday.
About CVE-2020-1147
CVE-2020-1147 is found in two .NET components (DataSet and DataTable) used to manage data sets, and affects Microsoft SharePoint, .NET Framework, and Visual Studio.
The vulnerability is triggered when the software fails to check the source markup of XML file input.
“An attacker who successfully exploited the vulnerability could run arbitrary code in the context of the process responsible for deserialization of the XML content. To exploit this vulnerability, an attacker could upload a specially crafted document to a server utilizing an affected product to process content,” Microsoft explained, and provided security updates for:
- .NET Core
- .NET Framework
- SharePoint Enterprise Server (2013 and 2016)
- SharePoint Server (2010 and 2019)
- Visual Studio (2017 and 2019).
“Full protection requires the installation of the .NET Framework update as well as updates for any additional affected products mentioned in this article,” the company stressed.
The vulnerability was reported by Oleksandr Mirosh from Micro Focus Fortify, Jonathan Birch of Microsoft Office Security Team, and Markus Wulftange of Code White GmbH.
Exploitation potential
Information security specialist and prolific bug hunter Steven Seeley decided to probe how the vulnerability might be exploited and recently shared how it can be leveraged against a SharePoint Server instance to achieve RCE as a low privileged user. He also provided a PoC.
“Microsoft rate this bug with an exploitability index rating of 1 and we agree, meaning you should patch this immediately if you haven’t. It is highly likley that this gadget chain can be used against several applications built with .net so even if you don’t have a SharePoint Server installed, you are still impacted by this bug,” he noted.
The call for immediate patching has been echoed by other security researchers:
I'd argue that CVE-2020-1147 is the issue you should be scrambling to fix, not the "wormable" DNS thing. Empirically deserialization RCEs are way more likely to see malicious exploitation compared to memory corruption bugs that weren't exploited in the wild prior to patch. https://t.co/7DyaRJMkIM
— Ben Hawkes (@benhawkes) July 20, 2020
You definitely want to patch CVE-2020-1147 if you present SharePoint to the Internet, or @blowdart will come around to your house. https://t.co/7giQ0Bb494
— Kevin Beaumont (@GossiTheDog) July 20, 2020
Vulnerabilities in Microsoft SharePoint, a web-based collaborative platform that integrates with Microsoft Office and usually houses a lot of sensitive data, have lately been an attractive target for hackers.