CVE-2025-39540 Overview
CVE-2025-39540 is a DOM-Based Cross-Site Scripting (XSS) vulnerability in the Rhys Wynne WP Flipclock plugin for WordPress. The flaw stems from improper neutralization of input during web page generation, classified under [CWE-79]. It affects all versions of wp-flipclock up to and including 1.9.1. Attackers can inject malicious script content that executes in the browser context of victims who interact with a crafted request. Exploitation requires low-privileged authentication and user interaction, and the scope change means the impact can extend beyond the vulnerable component.
Critical Impact
Authenticated attackers can execute arbitrary JavaScript in a victim's browser session, enabling session hijacking, credential theft, and unauthorized actions within WordPress sites running WP Flipclock 1.9.1 or earlier.
Affected Products
- Rhys Wynne WP Flipclock (wp-flipclock) WordPress plugin
- All versions from n/a through 1.9.1
- WordPress sites with the plugin installed and active
Discovery Timeline
- 2025-04-16 - CVE-2025-39540 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-39540
Vulnerability Analysis
The vulnerability is a DOM-Based XSS flaw in the WP Flipclock plugin. DOM-Based XSS occurs when client-side JavaScript writes attacker-controlled input into the Document Object Model without proper sanitization or output encoding. Unlike reflected or stored XSS, the malicious payload executes entirely within the browser and often never traverses the server in its executable form.
An authenticated attacker with low privileges can craft input that the plugin processes and renders into the DOM. When a victim loads the affected page or triggers the interaction, the injected script executes with the origin of the WordPress site. This enables session token theft, forced administrative actions, and pivoting into higher-privilege accounts.
Root Cause
The root cause is missing or insufficient input neutralization in the client-side rendering logic of wp-flipclock. User-supplied data is written directly into DOM sinks without escaping HTML metacharacters or validating context. See the Patchstack Vulnerability Advisory for technical details.
Attack Vector
Exploitation is network-based and requires the victim to interact with an attacker-supplied link or page element. The attacker needs authenticated access with low privileges to inject the payload. Because the CVSS scope is changed, script execution can affect resources outside the vulnerable plugin's security context, such as the broader WordPress admin session.
No public proof-of-concept exploit is available in Exploit-DB or referenced vendor resources at the time of publication.
Detection Methods for CVE-2025-39540
Indicators of Compromise
- Unexpected <script> tags, event handlers, or javascript: URIs rendered within pages that embed the WP Flipclock shortcode or widget
- WordPress user or option changes originating from administrator sessions without corresponding administrator activity
- Outbound HTTP requests from browser sessions to unfamiliar domains shortly after loading pages containing the flipclock component
Detection Strategies
- Inventory WordPress installations and identify sites running wp-flipclock version 1.9.1 or earlier
- Review plugin-generated content and post metadata for HTML entities, encoded payloads, or script fragments in fields consumed by the plugin
- Correlate authenticated low-privilege user activity with subsequent privilege changes or content modifications
Monitoring Recommendations
- Enable WordPress audit logging to capture post edits, option updates, and user role changes
- Deploy a web application firewall with rules that detect XSS payload patterns targeting known WordPress plugin parameters
- Monitor browser Content Security Policy (CSP) violation reports for inline script execution attempts on pages using the plugin
How to Mitigate CVE-2025-39540
Immediate Actions Required
- Identify all WordPress sites using WP Flipclock at version 1.9.1 or earlier
- Deactivate the wp-flipclock plugin until a patched release is confirmed installed
- Rotate credentials and session tokens for administrator accounts that may have interacted with affected pages
- Review recent changes to posts, users, and plugin configuration for unauthorized modifications
Patch Information
No fixed version is identified in the referenced advisory data. The vulnerability affects wp-flipclock from unspecified initial releases through 1.9.1. Consult the Patchstack Vulnerability Advisory for the current remediation status and apply any vendor-issued update as soon as it becomes available.
Workarounds
- Remove or deactivate the WP Flipclock plugin and replace it with a maintained alternative
- Restrict contributor and author-level accounts that could supply input processed by the plugin
- Deploy a Content Security Policy that disallows inline scripts and untrusted script sources to reduce DOM-Based XSS impact
- Apply virtual patching through a WAF rule that blocks script-like content in parameters handled by wp-flipclock
# Example: disable the plugin via WP-CLI pending vendor patch
wp plugin deactivate wp-flipclock
wp plugin list --name=wp-flipclock --fields=name,status,version
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
