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SECURITY ADVISORY / 01

CVE-2025-14548 Exploit & Vulnerability Analysis

Complete CVE-2025-14548 security advisory with proof of concept (PoC), exploit details, and patch analysis.

cve_patchdiff:calendar NVD ↗
Exploit PoC Vulnerability Patch Analysis

1. Vulnerability Background

  • What is this vulnerability?

    • CVE-2025-14548 is a stored cross-site scripting (XSS) vulnerability in the Calendar plugin for WordPress. It is triggered through the event_desc parameter when event data is created or updated.
    • The vulnerability occurs because user-supplied data from $_REQUEST is accepted and persisted without adequate sanitization, allowing HTML/JavaScript payloads to survive storage and execute later when a page renders the injected event description.

  • Why is it critical/important?

    • Stored XSS is high-risk because it can affect any user who views the compromised content, including site administrators.
    • In this case, an attacker with Contributor-level access or above can poison calendar event content. If an administrator has configured the plugin to allow lower-privilege users to manage events, the attacker can inject scripts that execute in the browser of any visitor or administrator.
    • The attack can lead to session theft, privilege escalation, unauthorized actions, and persistence inside the WordPress site.

  • What systems/versions are affected?

    • All versions of the Calendar plugin up to and including 1.3.16 are affected.
    • The issue exists in the plugin’s main file calendar.php and is triggered by the event creation/update workflow.

2. Technical Details

  • Root cause analysis

    • The vulnerable code reads request data directly from $_REQUEST and applies only stripslashes():
      • stripslashes($_REQUEST['event_desc'])
    • stripslashes() only removes backslashes from slashed input and does not sanitize or escape HTML or script content.
    • The plugin then uses these values in its event handling logic and eventually renders them in calendar pages without sufficient output escaping.

  • Attack vector and exploitation conditions

    • Attacker role: authenticated user with Contributor-level access or above.
    • Condition: administrator has enabled lower-privilege users to manage calendar events via plugin settings.
    • Attack flow:
      1. Attacker submits a calendar event with a malicious payload in event_desc (for example <script>alert(1)</script> or <img src=x>).
      2. The payload is stored in the plugin’s event data.
      3. When another user views the calendar page containing that event, the payload is delivered from storage and executed in the victim’s browser.

  • Security implications

    • Stored XSS in a WordPress plugin is particularly dangerous because it can execute in the context of an authenticated administrator session.
    • Potential impacts:
      • theft of authentication cookies or tokens
      • creation of persistent administrative backdoors
      • unauthorized changes to site configuration or content
      • use of the site as an XSS delivery vector for phishing or malware
    • Since the plugin also used $_REQUEST for multiple event fields, the attack surface extends beyond event_desc.

3. Patch Analysis

  • What code changes were made?

    • The patch replaces direct $_REQUEST handling and stripslashes() with:
      • wp_unslash($_REQUEST['...'])
      • wp_kses_post(...)
    • Example change:
      • Old: $desc = !empty($_REQUEST['event_desc']) ? stripslashes($_REQUEST['event_desc']) : '';
      • New: $desc = !empty($_REQUEST['event_desc']) ? wp_kses_post(wp_unslash($_REQUEST['event_desc'])) : '';
    • The same sanitization pattern was applied to related event fields: title, begin, end, time, recur, repeats, category, link.
    • Additional nonce handling was hardened in calendar.php:
      • old: if (wp_verify_nonce($_POST['_wpnonce'],'calendar-add') == false) {
      • new: if (!isset($_POST['_wpnonce']) || wp_verify_nonce(sanitize_text_field(wp_unslash($_POST['_wpnonce'])),'calendar-add') == false) {

  • How do these changes fix the vulnerability?

    • wp_unslash() normalizes WordPress-escaped input by removing added slashes, ensuring the raw user data is available for sanitization.
    • wp_kses_post() strips disallowed HTML tags and attributes, blocking script tags and dangerous event handlers from being stored in event fields.
    • The improved nonce check ensures that the request token is present and sanitized before verification, reducing risk from malformed or injected nonce values and preventing potential fatal errors.

  • Security improvements introduced

    • Input is now sanitized before it is persisted, reducing the chance of stored XSS.
    • A central sanitization routine is applied consistently across event fields.
    • Nonce validation is made more robust with explicit presence checks and sanitization.
    • The patch moves the plugin toward better WordPress security API usage.

4. Proof of Concept (PoC) Guide

  • Prerequisites for exploitation

    • WordPress installation with Calendar plugin version 1.3.16 or earlier.
    • Attacker account with Contributor-level access or higher.
    • Administrator has enabled the capability for lower-privilege users to manage calendar events.

  • Step-by-step exploitation approach

    1. Authenticate as a Contributor or equivalent user.
    2. Access the calendar event creation or edit interface.
    3. Set event description (event_desc) to a malicious payload:
      • Example: <script>fetch('/wp-admin/admin-ajax.php?...')</script>
    4. Submit the event.
    5. Visit the calendar page or any page where the event description is rendered.
    6. Observe the injected script executing in the browser context of the viewer.

  • Expected behavior vs exploited behavior

    • Expected behavior:
      • Event description should be treated as text or sanitized HTML.
      • No embedded scripts should execute.
    • Exploited behavior:
      • Malicious HTML/JavaScript persists in the database.
      • The payload executes when the event page is rendered.

  • How to verify the vulnerability exists

    • Confirm the plugin version is <=1.3.16.
    • Create or update an event with a simple payload like <script>alert('XSS')</script> in event_desc.
    • View the calendar page as another user.
    • If the alert triggers, the stored XSS is present.
    • On the patched version, the payload should be stripped or neutralized by wp_kses_post().

5. Recommendations

  • Mitigation strategies

    • Apply the patched version of the Calendar plugin immediately.
    • If patching is not possible, restrict event management to trusted roles and disable lower-privilege event editing.
    • Use Web Application Firewalls (WAFs) configured to detect XSS payloads in request bodies.

  • Detection methods

    • Review plugin source for direct use of $_REQUEST, stripslashes(), and missing wp_kses_* or sanitize_*.
    • Scan for stored event descriptions containing <script> or inline event handlers.
    • Monitor administrative and event-management actions for anomalous POST submissions.
    • Use automated vulnerability scanners that detect WordPress plugin XSS issues.

  • Best practices to prevent similar issues

    • Never trust client-supplied input; validate and sanitize all data before storage.
    • Use WordPress API functions appropriate to the data context:
      • wp_unslash() for raw request normalization
      • sanitize_text_field() for plain text
      • wp_kses_post() for limited HTML
      • esc_html(), esc_attr(), or esc_url() on output
    • Avoid using $_REQUEST; prefer $_POST or $_GET explicitly based on expected request method.
    • Implement and verify nonce checks consistently for state-changing actions.
    • Perform code review and security testing for plugin input handling and rendering paths.

Frequently asked questions about CVE-2025-14548

What is CVE-2025-14548?

CVE-2025-14548 is a security vulnerability. This security advisory provides detailed technical analysis of the vulnerability, exploit methodology, affected versions, and complete remediation guidance.

Is there a PoC (proof of concept) for CVE-2025-14548?

Yes. This writeup includes proof-of-concept details and a technical exploit breakdown for CVE-2025-14548. Review the analysis sections above for the PoC walkthrough and code examples.

How does CVE-2025-14548 get exploited?

The technical analysis section explains the vulnerability mechanics, attack vectors, and exploitation methodology. PatchLeaks publishes this information for defensive and educational purposes.

What products and versions are affected by CVE-2025-14548?

CVE-2025-14548 — check the affected-versions section of this advisory for specific version ranges, vulnerable configurations, and compatibility information.

How do I fix or patch CVE-2025-14548?

The patch analysis section provides guidance on updating to patched versions, applying workarounds, and implementing compensating controls.

What is the CVSS score for CVE-2025-14548?

The severity rating and CVSS scoring for CVE-2025-14548 is documented in the vulnerability details section. Refer to the NVD entry for the current authoritative score.