CVE-2026-0552: Simple Shopping Cart Plugin XSS Vulnerability

CVE-2026-0552 Overview

CVE-2026-0552 affects the Simple Shopping Cart plugin for WordPress in all versions up to and including 5.2.4. The vulnerability allows stored Cross-Site Scripting (XSS) through the plugin's wpsc_display_product shortcode. Attackers with contributor-level access or above can inject arbitrary JavaScript into pages via unsanitized shortcode attributes. The injected scripts execute in the browser of any user who views the affected page. The vulnerability is classified under [CWE-79] (Improper Neutralization of Input During Web Page Generation).

Critical Impact

Authenticated contributors can inject persistent JavaScript that executes against site visitors and administrators, enabling session theft, account takeover, and content defacement.

Affected Products

• WordPress Simple Shopping Cart plugin (also distributed as wordpress-simple-paypal-shopping-cart)
• All versions up to and including 5.2.4
• WordPress sites permitting contributor-level or higher user registration

Discovery Timeline

• 2026-04-04 - CVE-2026-0552 published to NVD
• 2026-04-24 - Last updated in NVD database

Technical Details for CVE-2026-0552

Vulnerability Analysis

The vulnerability resides in the wpsc_display_product shortcode handler of the Simple Shopping Cart plugin. The plugin accepts user-supplied attributes through the shortcode interface but fails to sanitize input before storage and fails to escape output during rendering. Contributor-level users can embed the shortcode in posts and supply attribute values containing JavaScript payloads. When WordPress renders the post, the malicious attributes are reflected directly into the HTML output. Any visitor or administrator viewing the page executes the attacker-controlled script within the site's origin.

Root Cause

The root cause is the absence of two complementary defenses. Input arriving via shortcode attributes is not validated or stripped of HTML control characters, and output rendering does not apply esc_attr() or esc_html() to attribute values before emitting them into the DOM. WordPress shortcode APIs do not automatically escape attributes, so plugin authors must explicitly call escaping functions. The Simple Shopping Cart plugin omits both steps.

Attack Vector

An attacker first obtains contributor-level access through self-registration or compromise of a low-privilege account. The attacker creates or edits a post containing the wpsc_display_product shortcode with a malicious attribute value, such as a payload that breaks out of an HTML attribute context using quote characters and an event handler like onmouseover or onerror. The post is submitted for review or published. When any user including administrators views the rendered page, the injected JavaScript executes with the privileges of that user's session. See the Wordfence Vulnerability Report for additional technical context.

Detection Methods for CVE-2026-0552

Indicators of Compromise

• Posts or pages containing [wpsc_display_product] shortcode invocations with attribute values that include <script>, javascript:, onerror=, onload=, or other event handler strings
• Outbound HTTP requests from visitor browsers to unfamiliar domains after viewing product-display pages
• New administrator accounts or modified user roles created shortly after contributor accounts authored content
• Anomalous session token usage from administrator accounts originating from new IP addresses

Detection Strategies

• Audit the wp_posts table for shortcode usage by contributor-level authors and inspect attribute payloads for HTML or JavaScript syntax
• Deploy Content Security Policy (CSP) headers in report-only mode to surface unexpected inline script execution
• Enable WordPress audit logging to track post creation and edits by contributor accounts
• Monitor web server access logs for requests to admin endpoints originating from sessions established immediately after rendering posts containing the shortcode

Monitoring Recommendations

• Alert on any database write that stores <script or on[a-z]+= patterns within shortcode attribute positions
• Track creation of new contributor or author accounts on sites running the affected plugin version
• Review WordPress plugin version inventories regularly and flag installations of wordpress-simple-paypal-shopping-cart at version 5.2.4 or below

How to Mitigate CVE-2026-0552

Immediate Actions Required

• Update the Simple Shopping Cart plugin to the version released after the fix committed in WordPress Changeset 3440173
• Audit all existing posts and pages for malicious wpsc_display_product shortcode attributes and remove suspicious content
• Review the user list and remove or downgrade contributor accounts that are not required
• Force password resets for all administrator accounts that may have viewed compromised pages

Patch Information

The vendor addressed the vulnerability in the changeset published at WordPress Changeset 3440173. The fix adds proper sanitization of shortcode attributes and escaping of attribute output. Site administrators should apply the update through the WordPress plugin management console or via WP-CLI using wp plugin update wordpress-simple-paypal-shopping-cart.

Workarounds

• Restrict user registration and disable the contributor role on sites where it is not operationally required
• Deploy a Web Application Firewall (WAF) rule that blocks requests containing event handler syntax or <script> tags in shortcode attribute parameters
• Implement a strict Content Security Policy that disallows inline scripts and unauthorized script sources
• Temporarily disable the Simple Shopping Cart plugin until patched if contributor-level accounts cannot be restricted

# Configuration example
wp plugin update wordpress-simple-paypal-shopping-cart
wp user list --role=contributor --field=user_login