CVE-2025-31462: CGM Event Calendar XSS Vulnerability

CVE-2025-31462 Overview

CVE-2025-31462 is a reflected Cross-Site Scripting (XSS) vulnerability in the rzfarrell CGM Event Calendar plugin for WordPress. The flaw stems from improper neutralization of user-supplied input during web page generation [CWE-79]. All plugin versions up to and including 0.8.5 are affected.

An attacker can craft a malicious URL containing JavaScript payloads. When a victim clicks the link, the payload executes in the victim's browser within the context of the vulnerable WordPress site. Successful exploitation can lead to session theft, credential harvesting, or unauthorized actions performed on behalf of the victim.

Critical Impact

Reflected XSS in CGM Event Calendar enables attackers to execute arbitrary JavaScript in victim browsers, potentially compromising authenticated WordPress sessions and exfiltrating sensitive data.

Affected Products

• CGM Event Calendar plugin (cgm-event-calendar) for WordPress
• All versions from initial release through 0.8.5
• WordPress sites with the vulnerable plugin installed and activated

Discovery Timeline

• 2025-04-01 - CVE-2025-31462 published to NVD
• 2026-04-23 - Last updated in NVD database

Technical Details for CVE-2025-31462

Vulnerability Analysis

The vulnerability is a reflected Cross-Site Scripting issue classified under [CWE-79]. The CGM Event Calendar plugin fails to properly sanitize or encode user-controlled input before reflecting it in HTTP responses. Input passed through request parameters is rendered directly into the HTML output without contextual escaping.

This allows attackers to inject arbitrary HTML and JavaScript into the rendered page. The attack requires user interaction, typically by tricking a victim into clicking a crafted link. Because the attack occurs across a security scope boundary, the injected script can affect resources beyond the vulnerable component.

The EPSS score is 0.219% with a percentile of 44.421, indicating a moderate likelihood of exploitation activity relative to other published vulnerabilities.

Root Cause

The plugin reads input from HTTP request parameters and embeds the values directly into generated HTML responses. The code path lacks calls to WordPress sanitization functions such as esc_html(), esc_attr(), or wp_kses(). Without contextual output encoding, attacker-controlled characters such as <, >, ", and ' are interpreted as HTML markup by the browser.

Attack Vector

The attack is delivered over the network and requires no authentication. An attacker constructs a URL referencing a vulnerable plugin endpoint with a JavaScript payload embedded in a parameter. The attacker then distributes the URL through phishing emails, malicious advertisements, or social engineering. When a victim visits the link, the server reflects the payload into the response, and the victim's browser executes the script.

For technical details, refer to the Patchstack XSS Vulnerability Advisory.

Detection Methods for CVE-2025-31462

Indicators of Compromise

• HTTP request logs containing URL parameters with encoded <script>, onerror=, onload=, or javascript: patterns targeting cgm-event-calendar endpoints
• Unexpected outbound requests from user browsers to attacker-controlled domains after visiting calendar pages
• WordPress administrator session anomalies, including logins from unusual IP addresses following calendar page interaction
• Referrer headers pointing to suspicious external URLs preceding administrative actions

Detection Strategies

• Inspect web server access logs for requests to CGM Event Calendar plugin paths containing HTML entities, percent-encoded angle brackets, or JavaScript keywords in query strings
• Deploy a Web Application Firewall (WAF) with rules to flag reflected XSS payload patterns targeting WordPress plugin parameters
• Enable WordPress security logging plugins to capture parameter values passed to plugin endpoints
• Correlate browser console errors and Content Security Policy violation reports with calendar page visits

Monitoring Recommendations

• Monitor WordPress plugin inventories and version data to identify installations of cgm-event-calendar at or below 0.8.5
• Establish alerts for outbound HTTP requests from end-user workstations to newly registered or low-reputation domains following WordPress site visits
• Track administrative account creation, role changes, and privilege grants on sites running the affected plugin

How to Mitigate CVE-2025-31462

Immediate Actions Required

• Inventory all WordPress installations and identify sites running the CGM Event Calendar plugin at version 0.8.5 or earlier
• Deactivate and remove the CGM Event Calendar plugin until a patched release is verified
• Implement a Web Application Firewall rule set that blocks reflected XSS payload signatures targeting WordPress plugin parameters
• Force password resets and session invalidation for WordPress administrators on affected sites

Patch Information

At the time of publication, no fixed version is identified in the NVD record. The vulnerability affects CGM Event Calendar through version 0.8.5. Administrators should monitor the Patchstack XSS Vulnerability Advisory and the WordPress plugin repository for updates.

Workarounds

• Remove or disable the cgm-event-calendar plugin until a patched version is published
• Deploy a strict Content Security Policy (CSP) header restricting inline script execution and limiting script sources to trusted origins
• Apply WAF virtual patching rules that filter request parameters for HTML and JavaScript metacharacters
• Restrict access to WordPress administrative interfaces using IP allowlists and multi-factor authentication

# Example Content Security Policy header for WordPress (nginx)
add_header Content-Security-Policy "default-src 'self'; script-src 'self'; object-src 'none'; base-uri 'self'; frame-ancestors 'self';" always;

# Example WAF rule pattern (ModSecurity) to flag reflected XSS attempts
SecRule ARGS "@rx (?i)(<script|onerror=|onload=|javascript:)" \
    "id:1003162,phase:2,deny,status:403,msg:'Possible reflected XSS targeting CGM Event Calendar'"