CVE-2025-26938

Executive Summary

CVE-2025-26938 is a Stored Cross-Site Scripting (XSS) vulnerability in the WordPress plugin Countdown Timer by bPlugins, affecting versions up to and including 1.2.6. The vulnerability arises from improper neutralization of user-supplied input during web page generation, allowing an authenticated attacker with contributor-level privileges or higher to inject arbitrary JavaScript into the plugin’s output. This injected script executes in the context of any user viewing the affected page, potentially leading to session hijacking, credential theft, or defacement. The CVSS v3.1 base score is 6.5 (Medium), with a vector emphasizing low attack complexity, required privileges, and user interaction. No public exploit code or patch is currently available, making proactive detection and mitigation critical.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Users are advised to monitor the plugin’s update channel and apply any security patches immediately upon release. Since the plugin is part of the WordPress ecosystem, supply chain risk is elevated if the plugin is used in production environments without proper code review or automated scanning.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L
• Base Score: 6.5 (Medium)
• Attack Vector (AV): Network – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low – No special conditions are required.
• Privileges Required (PR): Low – An attacker needs contributor-level access to the WordPress site.
• User Interaction (UI): Required – The victim must visit the compromised page.
• Scope (S): Changed – The injected script can affect resources beyond the vulnerable component.
• Confidentiality (C): Low – Limited data exposure possible.
• Integrity (I): Low – Content can be modified.
• Availability (A): Low – Minor service disruption possible.

Threat Level: Medium. While the CVSS score is moderate, the potential for stored XSS in a widely used plugin could lead to significant impact in multi-user WordPress environments.

Deep Dive & Mechanics

The vulnerability resides in the countdown-time plugin, which generates countdown timers via shortcodes. The plugin fails to sanitize or escape user-supplied attributes (e.g., title, message, or custom CSS classes) before rendering them in the HTML output. An attacker with contributor-level privileges can craft a shortcode containing malicious JavaScript, such as:

[countdown-time title="<script>alert('XSS')</script>"]

When the page is rendered, the script executes in the browser of any visitor, including administrators. The stored nature of the XSS means the payload persists in the database and affects all subsequent page loads.

Vulnerable vs. Patched Code

Vulnerable Code (version <= 1.2.6): The plugin likely outputs shortcode attributes directly without escaping:

echo '<div class="countdown-timer" data-title="' . $atts['title'] . '">';

Patched Code (hypothetical): A secure version would use WordPress’s esc_attr() or wp_kses() functions:

echo '<div class="countdown-timer" data-title="' . esc_attr($atts['title']) . '">';

Since no official patch is available, users must manually apply input validation and output encoding.

Exploitation & Lab Setup

Red Team (Attack Simulation)

1. Prerequisites: Obtain contributor-level credentials on a WordPress site running Countdown Timer <= 1.2.6.
2. Craft Payload: Create a post or page with a shortcode containing a stored XSS payload:

   [countdown-time title="<img src=x onerror=alert(document.cookie)>"]
   

3. Trigger: Publish the content and wait for an administrator or visitor to view the page.
4. Impact: The injected script executes, potentially exfiltrating session cookies or performing actions on behalf of the victim.

Blue Team (Detection & Defense)

1. Monitor Shortcode Usage: Audit posts/pages for suspicious shortcode attributes containing HTML or JavaScript.
2. Web Application Firewall (WAF): Deploy rules to block requests with <script> or onerror in shortcode parameters.
3. Content Security Policy (CSP): Implement a strict CSP to prevent inline script execution.
4. User Education: Restrict contributor-level access to trusted users only.

Indicators of Compromise (IOCs)

• File Hashes (SHA-256): (None available – plugin files unchanged)
• Suspicious Shortcodes: Posts/pages containing shortcodes with onerror, onload, <script>, or javascript: in attributes.
• Network Traffic: Outbound connections to attacker-controlled domains from the WordPress admin panel.
• Log Entries: Unusual wp_ajax or wp_post requests with encoded payloads in shortcode parameters.

Detection Engineering

YARA Rule

rule CVE_2025_26938_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads in Countdown Timer shortcode attributes"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-26938"
    strings:
        $shortcode = /\[countdown-time[^\]]*?title\s*=\s*["'][^"']*?(<script|onerror|onload|javascript:)/i
    condition:
        $shortcode
}

Sigma Rule

title: Stored XSS via Countdown Timer Shortcode
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects stored XSS attempts in WordPress Countdown Timer plugin
author: Valters IT
logsource:
    category: webserver
    product: wordpress
detection:
    selection:
        http.url|contains: "countdown-time"
        http.body|contains|all:
            - "title="
            - "<script"
    condition: selection
falsepositives:
    - Legitimate use of HTML in shortcode attributes (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-26938 Stored XSS in Countdown Timer"; flow:to_server,established; content:"countdown-time"; http_uri; content:"title="; http_client_body; pcre:"/<script|onerror|onload|javascript:/i"; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Disable the Countdown Timer plugin until a patch is released.
2. Short-Term Fix: Manually edit the plugin’s PHP files to add output escaping using esc_attr() or wp_kses().
3. Long-Term Fix: Monitor the WordPress plugin repository for an official update and apply it promptly.
4. Compensating Controls: Implement a Web Application Firewall (WAF) with rules to block XSS payloads in shortcode parameters.
5. User Access Control: Restrict contributor-level privileges to only trusted users and audit existing accounts.

Valters IT
DevSecOps & Cyber Threat Intelligence