CVE-2025-26536: Another Events Calendar XSS Vulnerability

CVE-2025-26536 Overview

CVE-2025-26536 is a Reflected Cross-Site Scripting (XSS) vulnerability affecting the Another Events Calendar WordPress plugin developed by Yendif Player. The vulnerability stems from improper neutralization of user-supplied input during web page generation, allowing attackers to inject malicious scripts that execute in the context of a victim's browser session.

Critical Impact

Attackers can exploit this Reflected XSS vulnerability to steal session cookies, hijack user accounts, redirect users to malicious websites, or perform actions on behalf of authenticated users including WordPress administrators.

Affected Products

• Another Events Calendar WordPress Plugin version 1.7.0 and earlier
• All WordPress installations running vulnerable versions of the another-events-calendar plugin

Discovery Timeline

• 2025-03-26 - CVE-2025-26536 published to NVD
• 2026-04-23 - Last updated in NVD database

Technical Details for CVE-2025-26536

Vulnerability Analysis

This vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation), which represents one of the most common web application security flaws. The Another Events Calendar plugin fails to properly sanitize user-controlled input before reflecting it back in the HTTP response, creating an attack surface for Reflected XSS attacks.

In a Reflected XSS scenario, the malicious payload is delivered through a crafted URL or form submission. When a victim clicks a malicious link or submits a manipulated form, the unsanitized input is processed by the vulnerable plugin and reflected back to the user's browser, where it executes as legitimate JavaScript code within the trusted WordPress domain context.

Root Cause

The root cause of CVE-2025-26536 lies in insufficient input validation and output encoding within the Another Events Calendar plugin. The plugin accepts user input through HTTP parameters without applying proper sanitization functions such as esc_html(), esc_attr(), or wp_kses() before rendering the content back to the browser. This allows specially crafted input containing JavaScript code to bypass security controls and execute in the victim's browser.

Attack Vector

The attack vector for this vulnerability is network-based and requires user interaction. An attacker must craft a malicious URL containing the XSS payload and convince a victim to click the link. This is typically accomplished through phishing emails, social engineering, or embedding the malicious link on compromised websites.

When the victim visits the malicious URL, the Another Events Calendar plugin processes the request and reflects the unsanitized payload in the response. The victim's browser interprets the injected content as legitimate JavaScript from the trusted WordPress site, executing the malicious code with access to the user's session data, cookies, and DOM.

The vulnerability requires no privileges to exploit but depends on social engineering to deliver the malicious link to potential victims. The impact extends beyond the vulnerable origin due to the changed scope, potentially affecting confidentiality, integrity, and availability of user data and sessions.

Detection Methods for CVE-2025-26536

Indicators of Compromise

• Suspicious URL parameters containing JavaScript code or HTML entities in requests to WordPress calendar endpoints
• Unusual JavaScript execution errors in browser console logs from calendar-related pages
• User reports of unexpected redirects or pop-ups when accessing calendar functionality
• Web server logs showing encoded script tags or event handlers in query strings

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block XSS payloads in HTTP parameters
• Monitor server access logs for requests containing encoded JavaScript or suspicious special characters
• Deploy browser-based XSS protection headers such as Content-Security-Policy (CSP) to detect policy violations
• Conduct regular security scans of WordPress installations to identify vulnerable plugin versions

Monitoring Recommendations

• Enable detailed logging for all WordPress plugin-related HTTP requests and responses
• Configure alerting for multiple failed XSS attempts from the same IP address or targeting the same endpoints
• Monitor for anomalous user session behavior that may indicate session hijacking attempts
• Regularly audit installed WordPress plugins and their versions against known vulnerability databases

How to Mitigate CVE-2025-26536

Immediate Actions Required

• Update the Another Events Calendar plugin to a version newer than 1.7.0 as soon as a patched version is available
• Temporarily deactivate the Another Events Calendar plugin if calendar functionality is not critical
• Implement Content Security Policy (CSP) headers to restrict inline JavaScript execution
• Deploy or update WAF rules to filter common XSS attack patterns

Patch Information

Organizations should monitor the Patchstack Vulnerability Report for updates regarding patches from the plugin developer. Until an official patch is released, administrators should implement compensating controls to protect against exploitation.

WordPress administrators should regularly check the plugin's official page and WordPress security advisories for updated versions that address this vulnerability.

Workarounds

• Implement a Content Security Policy header that disables inline script execution: Content-Security-Policy: script-src 'self'
• Configure WAF rules to block requests containing suspicious JavaScript patterns in URL parameters
• Restrict access to calendar functionality to authenticated users only where possible
• Consider using an alternative events calendar plugin until the vulnerability is patched

# WordPress .htaccess configuration to add security headers
<IfModule mod_headers.c>
    # Content Security Policy to mitigate XSS
    Header set Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'"
    
    # Additional security headers
    Header set X-Content-Type-Options "nosniff"
    Header set X-XSS-Protection "1; mode=block"
    Header set X-Frame-Options "SAMEORIGIN"
</IfModule>