Vulnerability Summary from Wordfence Intelligence
Description: LiteSpeed Cache <= 5.6 – Authenticated (Contributor+) Stored Cross-Site Scripting via Shortcode 
Affected Plugin: LiteSpeed Cache
Plugin Slug: litespeed-cache
Affected Versions: <= 5.6
CVE ID: CVE-2023-4372
CVSS Score: 6.4 (Medium)
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N
Researcher/s: Lana Codes 
Fully Patched Version: <= 5.7
The LiteSpeed Cache plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the ‘esi’ shortcode in versions up to, and including, 5.6 due to insufficient input sanitization and output escaping on user supplied attributes. This makes it possible for authenticated attackers with contributor-level and above permissions to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.
Technical Analysis
The LiteSpeed Cache is a site acceleration plugin with server-level cache and optimization. It provides a shortcode ([esi]) that can be used to cache blocks with Edge Side Includes technology when added to a WordPress page, if ESI was previously enabled in the settings.
Unfortunately, insecure implementation of the plugin’s shortcode functionality allows for the injection of arbitrary web scripts into these pages. Examining the vulnerable code reveals that the shortcode method in the ESI class does not adequately sanitize the user-supplied ‘cache’ input, and then fails to escape the ‘control’ output derived from the ‘cache’ parameter when it builds the ESI block. This makes it possible to inject attribute-based Cross-Site Scripting payloads via the ‘cache’ attribute.
[You can view these code snippets on the blog] 
This makes it possible for threat actors to carry out stored XSS attacks. Once a script is injected into a page or post, it will execute each time a user accesses the affected page. While this vulnerability does require that a trusted contributor account is compromised, or a user be able to register as a contributor, successful threat actors could steal sensitive information, manipulate site content, inject administrative users, edit files, or redirect users to malicious websites which are all severe consequences.
Shortcode Exploit Possibilities
Previous versions of WordPress contained a vulnerability that allowed shortcodes supplied by unauthenticated commenters to be rendered in certain configurations. This would make it possible for unauthenticated attackers to exploit this Cross-Site Scripting vulnerability on vulnerable installations. Fortunately, however, a vast majority of sites have been automatically upgraded to a patched release of WordPress as of this writing, which means most site owners do not need to be concerned about this. We still strongly recommend verifying your site has been updated to one of the patched versions of WordPress core found here. 
Disclosure Timeline
August 14, 2023 – Wordfence Threat Intelligence team discovers the stored XSS vulnerability in LiteSpeed Cache.
August 14, 2023 – We initiate contact with the plugin vendor asking that they confirm the inbox for handling the discussion.
August 14, 2023 – The vendor confirms the inbox for handling the discussion.
August 14, 2023 – We send over the full disclosure details. The vendor acknowledges the report and begins working on a fix.
August 16, 2023 – The vendor made the patch and sent us the GitHub commit.
October 10, 2023 – The fully patched version, 5.7, is released.
Conclusion
In this blog post, we have detailed a stored XSS vulnerability within the LiteSpeed Cache plugin affecting versions 5.6 and earlier. This vulnerability allows authenticated threat actors with contributor-level permissions or higher to inject malicious web scripts into pages that execute when a user accesses an affected page. The vulnerability has been fully addressed in version 5.7 of the plugin.
We encourage WordPress users to verify that their sites are updated to the latest patched version of LiteSpeed Cache.
All Wordfence users, including those running Wordfence Premium , Wordfence Care , and Wordfence Response , as well as sites still running the free version of Wordfence, are fully protected against this vulnerability.
If you know someone who uses this plugin on their site, we recommend sharing this advisory with them to ensure their site remains secure, as this vulnerability poses a significant risk.
For security researchers looking to disclose vulnerabilities responsibly and obtain a CVE ID, you can submit your findings to Wordfence Intelligence  and potentially earn a spot on our leaderboard .