A remote code execution vulnerability exists when the Microsoft XML Core Services MSXML parser processes user input. An attacker who successfully exploited the vulnerability could run malicious code remotely to take control of the user’s system. To exploit the vulnerability, an attacker could host a specially crafted website designed to invoke MSXML through a web browser. However, an attacker would have no way to force a user to visit such a website. Instead, an attacker would typically have to convince a user to either click a link in an email message or instant message that would then take the user to the website. When Internet Explorer parses the XML content, an attacker could run malicious code remotely to take control of the user’s system. The update addresses the vulnerability by correcting how the MSXML parser processes user input.
The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Windows_10 | Microsoft | - (including) | - (including) |
| Windows_10 | Microsoft | 1607 (including) | 1607 (including) |
| Windows_10 | Microsoft | 1703 (including) | 1703 (including) |
| Windows_10 | Microsoft | 1709 (including) | 1709 (including) |
| Windows_10 | Microsoft | 1803 (including) | 1803 (including) |
| Windows_10 | Microsoft | 1809 (including) | 1809 (including) |
| Windows_10 | Microsoft | 1903 (including) | 1903 (including) |
| Windows_7 | Microsoft | –sp1 (including) | –sp1 (including) |
| Windows_8.1 | Microsoft | - (including) | - (including) |
| Windows_rt_8.1 | Microsoft | - (including) | - (including) |
| Windows_server_2008 | Microsoft | –sp2 (including) | –sp2 (including) |
| Windows_server_2008 | Microsoft | r2-sp1 (including) | r2-sp1 (including) |
| Windows_server_2012 | Microsoft | - (including) | - (including) |
| Windows_server_2012 | Microsoft | r2 (including) | r2 (including) |
| Windows_server_2016 | Microsoft | - (including) | - (including) |
| Windows_server_2016 | Microsoft | 1803 (including) | 1803 (including) |
| Windows_server_2016 | Microsoft | 1903 (including) | 1903 (including) |
| Windows_server_2019 | Microsoft | - (including) | - (including) |
XML documents optionally contain a Document Type Definition (DTD), which, among other features, enables the definition of XML entities. It is possible to define an entity by providing a substitution string in the form of a URI. The XML parser can access the contents of this URI and embed these contents back into the XML document for further processing. By submitting an XML file that defines an external entity with a file:// URI, an attacker can cause the processing application to read the contents of a local file. For example, a URI such as “file:///c:/winnt/win.ini” designates (in Windows) the file C:\Winnt\win.ini, or file:///etc/passwd designates the password file in Unix-based systems. Using URIs with other schemes such as http://, the attacker can force the application to make outgoing requests to servers that the attacker cannot reach directly, which can be used to bypass firewall restrictions or hide the source of attacks such as port scanning. Once the content of the URI is read, it is fed back into the application that is processing the XML. This application may echo back the data (e.g. in an error message), thereby exposing the file contents.