CVE-2025-9378: Vayu Blocks WordPress Plugin XSS Vulnerability

CVE-2025-9378 Overview

CVE-2025-9378 is a stored Cross-Site Scripting (XSS) vulnerability in the Vayu Blocks – Website Builder for the Block Editor plugin for WordPress. The flaw affects all versions up to and including 1.3.9. It stems from insufficient input sanitization and output escaping on multiple attributes within the plugin's Lottie block. Authenticated users with Contributor-level access or higher can inject arbitrary JavaScript that executes when any visitor views an affected page. The issue is tracked under CWE-79 and was patched in version 1.4.0 through WordPress Changeset #3351839.

Critical Impact
Contributor-level attackers can persist arbitrary JavaScript in published pages, enabling session hijacking, credential theft, and administrative account takeover when viewed by higher-privileged users.

Affected Products

Vayu Blocks – Website Builder for the Block Editor (WordPress plugin)
All versions ≤ 1.3.9
Sites running the vulnerable Lottie block renderer at inc/render/lottie/lottie.php

Discovery Timeline

2025-09-03 - CVE-2025-9378 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-9378

Vulnerability Analysis

The Vayu Blocks plugin renders Lottie animation blocks server-side using attributes supplied through the WordPress block editor. Multiple attributes passed to the Lottie render function are concatenated into HTML output without being sanitized on input or escaped on output. Any user able to insert or edit blocks on a post, including Contributor-level accounts, can embed JavaScript payloads inside those attributes. When an administrator, editor, or site visitor loads the resulting page, the browser executes the stored script in the context of the site origin.

Stored XSS in a WordPress block context is particularly useful to attackers because the payload persists in the database and fires on every page view. In practice, Contributor accounts are often provisioned loosely for guest authors, giving attackers a realistic foothold to escalate toward administrator takeover through actions such as creating new admin users, altering plugin or theme files, or injecting backdoors.

Root Cause

The vulnerable rendering logic in the plugin's lottie.php file (visible in the 1.3.5 source reference) emits block attributes directly into HTML without passing them through WordPress sanitization helpers such as esc_attr(), esc_url(), or wp_kses(). The fix shipped in Changeset #3351839 adds proper escaping on the affected attributes.

Attack Vector

The attack is remote and authenticated. An attacker with Contributor privileges creates or edits a post, inserts a Lottie block, and supplies a crafted attribute value containing a JavaScript payload (for example, within an event handler or javascript: URL). The payload is stored in the post content. When any user, including unauthenticated visitors or privileged reviewers, loads the page, the script executes in their browser session.

The vulnerability mechanism is described in prose only; no public proof-of-concept exploit code has been verified. Technical details are available in the Wordfence advisory.

Detection Methods for CVE-2025-9378

Indicators of Compromise

Lottie blocks in post content containing HTML event handlers such as onload=, onerror=, or onclick= within attribute values
javascript: URIs stored in Lottie block attributes (source paths, link URLs)
Unexpected <script> tags or encoded script payloads inside wp_posts.post_content for posts authored by Contributor accounts
New administrator accounts, modified user roles, or altered plugin files appearing shortly after a Contributor edits a post

Detection Strategies

Query the WordPress database for Lottie block markup containing suspicious strings: SELECT ID, post_author FROM wp_posts WHERE post_content LIKE '%wp:vayu-blocks/lottie%' AND (post_content LIKE '%javascript:%' OR post_content REGEXP 'on[a-z]+=');
Review web server access logs for outbound requests from browsers to attacker-controlled domains referenced from pages hosting Lottie blocks
Monitor WordPress audit logs for post edits by Contributor-level users that insert or modify Vayu Blocks Lottie components

Monitoring Recommendations

Enable a WordPress activity log plugin to track post revisions and block attribute changes by low-privilege users
Deploy a Content Security Policy (CSP) that restricts inline script execution and report violations to a monitoring endpoint
Alert on creation of new administrator accounts or privilege changes following post edits by non-admin users

How to Mitigate CVE-2025-9378

Immediate Actions Required

Update the Vayu Blocks plugin to version 1.4.0 or later on all WordPress sites
Audit existing posts and pages containing Lottie blocks for suspicious attribute values and remove any injected scripts
Review Contributor and Author accounts for legitimacy and reset credentials on any accounts suspected of abuse

Patch Information

The vendor remediated the vulnerability in version 1.4.0 via WordPress Changeset #3351839, which adds proper sanitization and escaping to the affected Lottie block attributes. See the Wordfence Vulnerability Report for additional detail.

Workarounds

Deactivate the Vayu Blocks plugin until the update to 1.4.0 can be applied
Restrict the Contributor role or require editorial review before publishing posts that include Vayu Blocks components
Enforce a strict Content Security Policy that blocks inline scripts and unauthorized external script sources to reduce exploitation impact

bash

# Update the plugin via WP-CLI
wp plugin update vayu-blocks --version=1.4.0

# Verify installed version
wp plugin get vayu-blocks --field=version

# Temporary workaround: deactivate until patched
wp plugin deactivate vayu-blocks