Helpful < 4.4.59 – Admin+ Stored Cross-Site Scripting | CVE 2021-24841

Description

The plugin does not sanitise and escape some of its settings, which could allow high privilege users to perform Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed

Proof of Concept

Put the following payload in the System > Miscellaneous > Custom Timezone setting of the plugin: "><details open ontoggle="alert(/XSS/)">
The XSS will be triggered when viewing the settings page

Put the following payload "><details open ontoggle="alert(/XSS/)"> in Texts > Before Voting / After Voting / Answer Buttons / Admin Columns > Feedback settings
The XSS will be triggered when viewing a post/page where with the Helpful Widget is displayed, or after a vote depending on the vulnerable field/s used

Put the following payload in the Feedback > Messages: "><details open ontoggle="alert(/XSS/)">

The plugin fixes from 4.4.56 to 4.4.58 were insufficient as not escaping data when output in attributes, allowing for payloads such as " style=animation-name:rotation onanimationstart=alert(/XSS/)//