CVE-2026-8623: Dear Flipbook <= 2.4.30 - Authenticated (Contributor+) Stored Cross-Site Scripting via '.dvcss' Element Class Attribute
The Dear Flipbook – PDF Flipbook, 3D Flipbook, PDF embed, PDF viewer plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'postcontent (class attribute of .dvcss element)' parameter in all versions up to, and including, 2.4.30 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The payload is embedded as a Base64-encoded JSON object in a CSS class name on a Custom HTML block; the frontend parseCSSElements() function decodes it client-side with atob() and JSON.parse() and renders the logo property as raw HTML, meaning no server-side or client-side sanitization intercepts the malicious script before DOM insertion.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Dear Flipbook – PDF Flipbook, 3D Flipbook, PDF embed, PDF viewer plugin for WordPressto a version that resolves this vulnerability.Fixed in 2.4.30 - Compensating control
Until fixed, review pages using the Custom HTML block that embeds Base64-encoded JSON in a CSS class name on a .dvcss element, and remove/block that content to prevent execution of injected scripts for contributor+ users.
Event History
Frequently Asked Questions
Who can exploit this issue?
An attacker needs an authenticated WordPress account with Contributor-level permissions or higher. They must be able to add malicious content to a page using a Custom HTML block.
When does the injected script execute?
The script executes in the browser whenever a user accesses a page containing the attacker’s injected content. The issue is stored XSS, so the attacker does not need to be present when victims view the page.
Are installations affected by default?
Exploitation depends on an authenticated user being able to create or modify content that includes the crafted .dvcss class attribute in a Custom HTML block. The provided data does not establish whether this condition exists in a default WordPress role or editor configuration.
How can administrators check for possible exploitation?
Review page content, particularly Custom HTML blocks, for .dvcss class attributes containing Base64-encoded JSON payloads. The vulnerable frontend code decodes such data and inserts the JSON logo property as raw HTML.