Testing for Naughty SOAP Attachments (OWASP-WS-006)

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Brief Summary

Binary files, including executables and document types that can contain malware, can be posted using a web service in several ways. These files can be sent as a parameter of a web service method; they can be sent as an attachment using SOAP with Attachments and they can be sent using DIME (Direct Internet Message Encapsulation) and WS-Attachments.

An attacker can craft an XML document (SOAP message) to send to a web service that contains malware as an attachment. Testing to ensure the Web Service host inspects SOAP attachments should be included in the web application testing plan.


Description of the Issue

This section describes attack vectors for Web Services that accept attachments. The danger exists in the processing of the attachment on the server and redistribution of the file to clients.


Black Box testing and example

Testing for file as parameter vulnerabilities:

1. Find WSDL that accepts attachments:

For example:

... <s:element name="UploadFile">
  <s:complexType>
  <s:sequence>
  <s:element minOccurs="0" maxOccurs="1" name="filename" type="s:string" /> 
  <s:element minOccurs="0" maxOccurs="1" name="type" type="s:string" /> 
  <s:element minOccurs="0" maxOccurs="1" name="chunk" type="s:base64Binary" /> 
  <s:element minOccurs="1" maxOccurs="1" name="first" type="s:boolean" /> 
 </s:sequence>
 </s:complexType>
 </s:element>
 <s:element name="UploadFileResponse">
 <s:complexType>
 <s:sequence>
 <s:element minOccurs="1" maxOccurs="1" name="UploadFileResult" type="s:boolean" /> 
 </s:sequence>
 </s:complexType>
 </s:element> ... 

2. Attach a test virus attachment using a non-destructive virus like EICAR, to a SOAP message and post to the target Web Service. In this example, EICAR is used.

Soap message with EICAR attachment (as Base64 data):

POST /Service/Service.asmx HTTP/1.1
Host: somehost
Content-Type: text/xml; charset=utf-8
Content-Length: length
SOAPAction: http://somehost/service/UploadFile

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"   xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<soap:Body>
<UploadFile xmlns="http://somehost/service">
<filename>eicar.pdf</filename>
<type>pdf</type>
<chunk>X5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*</chunk>
<first>true</first>
</UploadFile>
</soap:Body>
</soap:Envelope>

Result Expected:

A soap response with the UploadFileResult parameter set to true (this will vary per service). The eicar test virus file is allowed to be stored on the host server and can be redistributed as a PDF.

Testing for SOAP with Attachment vulnerabilities

The testing is similar, however the request would be similar to:

POST /insuranceClaims HTTP/1.1
Host: www.risky-stuff.com
Content-Type: Multipart/Related; boundary=MIME_boundary; type=text/xml;
        start="<claim061400a.xml@claiming-it.com>"
Content-Length: XXXX
SOAPAction: http://schemas.risky-stuff.com/Auto-Claim
Content-Description: This is the optional message description.

--MIME_boundary
Content-Type: text/xml; charset=UTF-8
Content-Transfer-Encoding: 8bit
Content-ID: <claim061400a.xml@claiming-it.com>

<?xml version='1.0' ?>
<SOAP-ENV:Envelope
xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">
<SOAP-ENV:Body>
<claim:insurance_claim_auto id="insurance_claim_document_id"
xmlns:claim="http://schemas.risky-stuff.com/Auto-Claim">
<theSignedForm href="cid:claim061400a.tiff@claiming-it.com"/>
<theCrashPhoto href="cid:claim061400a.jpeg@claiming-it.com"/>
<!-- ... more claim details go here... -->
</claim:insurance_claim_auto>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>

--MIME_boundary
Content-Type: image/tiff
Content-Transfer-Encoding: base64
Content-ID: <claim061400a.tiff@claiming-it.com>

...Base64 encoded TIFF image...
--MIME_boundary
Content-Type: image/jpeg
Content-Transfer-Encoding: binary
Content-ID: <claim061400a.jpeg@claiming-it.com>

...Raw JPEG image..
--MIME_boundary-- 

Gray Box testing and example

Testing for Topic X vulnerabilities: ... Result Expected: ...



References

Xml.com (http://www.xml.com/pub/a/2003/02/26/binaryxml.html) W3C Soap with Attachments (http://www.w3.org/TR/SOAP-attachments)

Tools

EICAR (http://www.eicar.org/anti_virus_test_file.htm)