Exploit the possiblities

SilverStrip CMS 3.5.3 Cross Site Scripting

SilverStrip CMS 3.5.3 Cross Site Scripting
Posted Sep 15, 2017
Authored by Siddhartha Tripathy | Site sec-consult.com

SilverStripe CMS versions 3.5.3 and below suffer from a persistent cross site scripting vulnerability.

tags | exploit, xss
MD5 | 4488225884421348eca56ef59a92eb22

SilverStrip CMS 3.5.3 Cross Site Scripting

Change Mirror Download
SEC Consult Vulnerability Lab Security Advisory < 20170914-1 >
title: Persistent Cross-Site Scripting
product: SilverStripe CMS
vulnerable version: <=3.5.3
fixed version: 3.6.1
impact: Medium
homepage: https://www.silverstripe.org/
found: 2017-03-15
by: S. Tripathy (Office Singapore)
SEC Consult Vulnerability Lab

An integrated part of SEC Consult
Bangkok - Berlin - Linz - Luxembourg - Montreal - Moscow
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Vendor description:
"SilverStripe is the intuitive content management system and flexible
framework loved by editors and developers alike. Equip your web teams
to achieve outstanding results."

Source: https://www.silverstripe.org/

Business recommendation:
SEC Consult recommends to do a proper output sanitization on uploaded
SVG files. Users should upgrade to version 3.6.1 or higher. A thorough
source code analysis is recommended.

Vulnerability overview/description:
1) Persistant Cross Site Scripting
Due to the lack of input validation and output sanitization,
an attacker can upload SVG files containing malicious JavaScript
code to be executed under a victim's browser context.

Proof of concept:
1) Persistant Cross Site Scripting
Example: XSS using SVG File Upload

The file upload function in the CMS allows to upload SVG files.
But it doesn't sanitize output of the file which leads to XSS.

There are 2 vulnerable instances of the same vulnerability.
1: The "Insert Media" option in the content editor.
2: The path "/admin/assets/add/"

During editing contents or creating a new page an attacker can upload
an SVG image using the "Insert Image" button.

The request below shows that an attacker can upload an SVG file with
malicious payloads.
POST /admin/pages/edit/EditorToolbar/MediaForm/field/AssetUploadField/upload HTTP/1.1
Host: $host
Cookie: PHPSESSID=esqs7da6338k0sgj7itn3tcil7; bypassStaticCache=1
Connection: close

Content-Disposition: form-data; name="SecurityID"

Content-Disposition: form-data; name="AssetUploadField"; filename="evilsvgfile.svg"
Content-Type: image/svg+xml

<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"

<svg version="1.1" baseProfile="full" xmlns="http://www.w3.org/2000/svg">
<polygon id="triangle" points="0,0 0,50 50,0" fill="#009900" stroke="#004400"/>
<script type="text/javascript">

Using the same process an attacker can also upload a malicious SVG file in the path

A low privilege editor user such as a "Content Editor" can also exploit this

Vulnerable / tested versions:
The following version is affected by the identified vulnerabilities which
was the most recent version at the time of discovery:

Silverstripe CMS version <=3.5.3

Vendor contact timeline:
2017-03-22: Contacting vendor through security@silverstripe.org
2017-03-23: Vendor provided public key certificates
2017-03-23: Sent the advisory to vendor
2017-04-17: Follow-up with vendor on the status
2017-04-17: Vendor responded work in progress
2017-05-09: Follow-up with vendor on the status, no response from the vendor
2017-05-24: Informed the vendor on releasing the advisory
2017-05-31: Vendor: vulnerability has been fixed, verified that it is not
2017-06-07: Vendor confirmed that the issue is not fixed and it will be fixed in
the next release.
2017-06-27: Silverstripe Version 3.6.1 released
2017-09-14: Public release of advisory

Upgrade to SilverStripe v3.6.1

Changelog: https://docs.silverstripe.org/en/3/changelogs/3.6.1

Do not allow uploading an SVG file.

Advisory URL:


SEC Consult Vulnerability Lab

SEC Consult
Bangkok - Berlin - Linz - Luxembourg - Montreal - Moscow
Kuala Lumpur - Singapore - Vienna (HQ) - Vilnius - Zurich

About SEC Consult Vulnerability Lab
The SEC Consult Vulnerability Lab is an integrated part of SEC Consult. It
ensures the continued knowledge gain of SEC Consult in the field of network
and application security to stay ahead of the attacker. The SEC Consult
Vulnerability Lab supports high-quality penetration testing and the evaluation
of new offensive and defensive technologies for our customers. Hence our
customers obtain the most current information about vulnerabilities and valid
recommendation about the risk profile of new technologies.

Interested to work with the experts of SEC Consult?
Send us your application https://www.sec-consult.com/en/career/index.html

Interested in improving your cyber security with the experts of SEC Consult?
Contact our local offices https://www.sec-consult.com/en/contact/index.html

Mail: research at sec-consult dot com
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Blog: http://blog.sec-consult.com
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EOF Siddhartha Tripathy / @2017


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