CVE-2025-49881: Responsive Blocks Stored XSS Vulnerability

CVE-2025-49881 Overview

CVE-2025-49881 is a stored cross-site scripting (XSS) vulnerability in the CyberChimps Responsive Blocks plugin (responsive-block-editor-addons) for WordPress. The flaw affects all plugin versions up to and including 2.0.5. Authenticated contributors can inject malicious JavaScript that persists in the database and executes in the browsers of users who view the affected content. The issue is categorized under CWE-79, Improper Neutralization of Input During Web Page Generation.

Critical Impact
Attackers with low-privilege accounts can store malicious scripts that execute in administrator sessions, enabling session theft, forced actions, and content manipulation across the WordPress site.

Affected Products

CyberChimps Responsive Blocks (responsive-block-editor-addons) WordPress plugin
All versions from n/a through 2.0.5
WordPress installations using the Gutenberg block editor with this plugin enabled

Discovery Timeline

2025-06-17 - CVE-2025-49881 published to the National Vulnerability Database
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-49881

Vulnerability Analysis

The vulnerability stems from improper neutralization of user-supplied input rendered within WordPress pages generated by the Responsive Blocks plugin. Block attributes accepted from the editor are not sufficiently sanitized or escaped before being written to the page markup. An authenticated user with contributor-level permissions can craft block content containing JavaScript payloads. Once a privileged user views the post or page, the script executes in that user's browser context.

The scope-changed nature of the finding reflects that exploitation can affect data and components beyond the attacker's own privilege boundary, including administrators who load the stored content. Successful exploitation can lead to session hijacking, administrative action forgery, defacement, or redirection of visitors to attacker-controlled destinations. Refer to the Patchstack advisory for additional technical context.

Root Cause

The root cause is missing or insufficient output escaping in one or more block render callbacks. WordPress provides helpers such as esc_html(), esc_attr(), and wp_kses_post() for safe output. When block attributes are concatenated directly into HTML without these helpers, HTML and JavaScript syntax in attacker-controlled fields is interpreted by the browser rather than displayed as literal text.

Attack Vector

Exploitation requires an authenticated session with permission to create or edit posts, typically a contributor account or higher. The attacker inserts a block supplied by Responsive Blocks and populates a vulnerable attribute with a crafted payload. User interaction is required: a victim must load the resulting page or preview. Because the plugin stores the payload in post content, the attack persists until the content is removed or sanitized.

No verified public proof-of-concept has been published for this issue. See the Patchstack entry for vendor-coordinated disclosure details.

Detection Methods for CVE-2025-49881

Indicators of Compromise

Post or page content containing <script> tags, inline on* event handlers, or javascript: URIs inside Responsive Blocks attributes
Unexpected outbound requests from administrator browser sessions following page previews or edits
New or modified administrator accounts created shortly after a contributor-authored post was viewed
WordPress option or user metadata changes with no corresponding audit trail

Detection Strategies

Query the wp_posts table for block markup from responsive-block-editor-addons containing script tags or event handler attributes
Review WordPress audit logs for contributor-role users publishing or updating posts that contain Responsive Blocks
Deploy a web application firewall rule to flag block attributes containing HTML control characters or script keywords

Monitoring Recommendations

Monitor administrator browser telemetry for anomalous XHR or fetch requests to /wp-json/wp/v2/users or /wp-admin/admin-ajax.php
Alert on creation of new administrator accounts or role elevations outside change windows
Track plugin version inventory across WordPress sites to identify installations still running 2.0.5 or earlier

How to Mitigate CVE-2025-49881

Immediate Actions Required

Update the Responsive Blocks plugin to the latest version above 2.0.5 as soon as the vendor releases a fix
Audit existing posts and pages that use Responsive Blocks for suspicious script content and remove any malicious payloads
Restrict contributor-level and author-level account creation and review existing low-privilege accounts for legitimacy

Patch Information

Consult the Patchstack advisory for Responsive Blocks for the latest patched version and update guidance. Apply updates through the WordPress plugin manager or via WP-CLI, then verify the installed version matches the fixed release.

Workarounds

Temporarily deactivate the Responsive Blocks plugin until a patched version is installed
Enforce least privilege by limiting post-publishing permissions to trusted users only
Deploy a web application firewall rule set that blocks XSS payloads in POST requests to /wp-admin/post.php and the REST API block endpoints
Enable a strict Content Security Policy that disallows inline scripts on the WordPress front end and admin interface

bash

# Update Responsive Blocks via WP-CLI once a fixed version is available
wp plugin update responsive-block-editor-addons

# Verify installed version is greater than 2.0.5
wp plugin get responsive-block-editor-addons --field=version

# Temporary mitigation: deactivate the plugin
wp plugin deactivate responsive-block-editor-addons