CVE-2026-0549: Groups Plugin WordPress XSS Vulnerability

CVE-2026-0549 Overview

The Groups plugin for WordPress is vulnerable to Stored Cross-Site Scripting (XSS) via the plugin's groups_group_info shortcode in all versions up to, and including, 3.10.0. The vulnerability exists due to insufficient input sanitization and output escaping on user-supplied attributes, allowing authenticated attackers with contributor-level access and above to inject arbitrary web scripts into pages. These malicious scripts execute whenever a user accesses an injected page, potentially leading to session hijacking, defacement, or further attacks against site visitors.

Critical Impact

Authenticated attackers can inject persistent malicious scripts that execute in the browsers of all users viewing affected pages, potentially compromising user sessions and sensitive data.

Affected Products

• WordPress Groups plugin versions up to and including 3.10.0
• WordPress sites utilizing the groups_group_info shortcode functionality
• Any WordPress installation with contributor-level or higher user accounts using the vulnerable plugin

Discovery Timeline

• 2026-02-19 - CVE-2026-0549 published to NVD
• 2026-02-19 - Last updated in NVD database

Technical Details for CVE-2026-0549

Vulnerability Analysis

This Stored Cross-Site Scripting vulnerability (CWE-79) affects the Groups plugin's shortcode processing functionality. The groups_group_info shortcode fails to properly sanitize and escape user-supplied attributes before rendering them in the page output. When an authenticated user with at least contributor-level privileges crafts a malicious shortcode with embedded JavaScript, the payload is stored in the WordPress database and subsequently executed in the browsers of any users who view the affected page.

The vulnerability is particularly concerning because it persists across page loads and affects all visitors to the compromised page, not just the attacker. This makes it an effective vector for widespread session hijacking, credential theft, or distribution of malware to site visitors.

Root Cause

The root cause lies in the insufficient input validation and output escaping within the class-groups-shortcodes.php file. The shortcode handler accepts user-controlled attributes and renders them without properly sanitizing the input or escaping the output. This allows specially crafted attribute values containing JavaScript to be stored and later executed when the page content is rendered. The vulnerable code path can be examined in the WordPress Groups Shortcode Code.

Attack Vector

The attack requires network access and authenticated access with at least contributor-level permissions to the WordPress site. An attacker would craft a post or page containing the groups_group_info shortcode with malicious JavaScript embedded in one of its attributes. Since contributors can create and save posts (pending review in default configurations), the malicious payload gets stored in the database. When an administrator, editor, or any visitor views the page—either in preview or after publication—the injected script executes in their browser context.

The attack does not require user interaction beyond viewing the page, and because the scope is changed (the vulnerability affects users other than the attacker), it can compromise authenticated sessions of higher-privileged users.

Detection Methods for CVE-2026-0549

Indicators of Compromise

• Presence of unexpected JavaScript code within groups_group_info shortcode attributes in post or page content
• Unusual script tags or event handlers (e.g., onload, onerror, onclick) within shortcode parameters
• Database entries containing encoded or obfuscated JavaScript within posts using the Groups plugin shortcodes
• Browser console errors or unexpected network requests when viewing pages with Groups shortcodes

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block XSS payloads in WordPress shortcode attributes
• Deploy content security policies (CSP) to mitigate the impact of injected scripts and alert on violations
• Use WordPress security plugins that scan post content for suspicious JavaScript patterns
• Monitor audit logs for posts created or modified by contributor-level users containing shortcode usage

Monitoring Recommendations

• Enable detailed logging for post creation and modification events, particularly for users with contributor-level access
• Implement real-time alerting for posts containing potentially malicious shortcode attribute patterns
• Conduct periodic security audits of stored content for XSS indicators
• Monitor browser error reports and CSP violation logs for evidence of exploitation attempts

How to Mitigate CVE-2026-0549

Immediate Actions Required

• Update the Groups plugin to a version newer than 3.10.0 that includes the security fix
• Review existing posts and pages for potentially malicious content in groups_group_info shortcode attributes
• Audit contributor-level and higher user accounts for suspicious activity
• Implement Content Security Policy headers to reduce the impact of any stored XSS payloads

Patch Information

The vulnerability has been addressed in a plugin update. The fix involves proper input sanitization and output escaping for user-supplied shortcode attributes. Technical details of the changes can be reviewed in the WordPress Changeset Update. Additional vulnerability details are available in the Wordfence Vulnerability Report.

Workarounds

• Temporarily disable the Groups plugin until the update can be applied if the shortcode functionality is not critical
• Restrict contributor-level user creation and audit existing contributor accounts
• Implement server-side input filtering to strip potentially malicious content from shortcode attributes
• Deploy a WAF with XSS protection rules specifically targeting WordPress shortcode abuse patterns

# Configuration example - Add Content Security Policy header in .htaccess
# This helps mitigate the impact of XSS by restricting script execution sources
<IfModule mod_headers.c>
    Header set Content-Security-Policy "script-src 'self'; object-src 'none';"
</IfModule>