CVE-2025-2809

Executive Summary

CVE-2025-2809 is a critical vulnerability in the WordPress plugin azurecurve Shortcodes in Comments, affecting all versions up to and including 2.0.2. The flaw allows unauthenticated attackers to execute arbitrary shortcodes by exploiting insufficient validation before the do_shortcode function is called. This can lead to unauthorized content injection, data exposure, or further compromise of the WordPress instance. The vulnerability has a CVSS score of 7.3 (High) and currently has no known patch or public exploit code. The EPSS score is 0.0%, indicating low exploitation likelihood at this time, but the risk remains significant due to the unauthenticated nature of the attack.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Users are advised to monitor for updates and consider disabling the plugin if no patch is available. No NPM, PyPI, Go, or Ruby packages are involved.

CVSS Breakdown & Threat Level

• CVSS Score: 7.3 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: Low

The vulnerability is easily exploitable remotely without authentication, making it a high-priority target for attackers.

Deep Dive & Mechanics

The plugin azurecurve Shortcodes in Comments allows users to embed shortcodes within WordPress comments. The vulnerability arises from the improper validation of user-supplied input before passing it to the do_shortcode() function. Specifically, the plugin does not sanitize or validate the shortcode content, allowing an attacker to inject arbitrary shortcodes that are then executed by WordPress.

WordPress shortcodes can perform a wide range of actions, including:

• Executing PHP code (if a vulnerable shortcode is present)
• Fetching and displaying sensitive data
• Modifying site content
• Initiating outbound HTTP requests

Since the attack is unauthenticated, any visitor to a WordPress site with this plugin enabled can exploit the flaw by submitting a crafted comment containing malicious shortcodes.

Vulnerable vs. Patched Code

Vulnerable Code (version <= 2.0.2): The plugin likely contains a function similar to:

function azc_shortcode_in_comments( $content ) {
    return do_shortcode( $content );
}
add_filter( 'comment_text', 'azc_shortcode_in_comments' );

This code directly passes the comment text to do_shortcode() without any validation.

Patched Code (hypothetical): A secure version would validate or sanitize the shortcode input:

function azc_shortcode_in_comments( $content ) {
    // Only allow specific shortcodes
    $allowed_shortcodes = array( 'my_safe_shortcode' );
    // Strip all shortcodes except allowed ones
    $content = strip_shortcodes( $content );
    // Re-add allowed shortcodes
    foreach ( $allowed_shortcodes as $shortcode ) {
        $content = str_replace( "[$shortcode]", do_shortcode( "[$shortcode]" ), $content );
    }
    return $content;
}
add_filter( 'comment_text', 'azc_shortcode_in_comments' );

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A WordPress site with azurecurve Shortcodes in Comments version <= 2.0.2 installed and active.
• Comments enabled on posts/pages.

Exploitation Steps:

1. Identify a target WordPress site running the vulnerable plugin.
2. Submit a comment containing a malicious shortcode, e.g.:

   [contact-form-7 id="123" title="Contact form 1"]
   

   Or a more dangerous shortcode if available:

   [php]echo 'Vulnerable';[/php]
   

3. The shortcode will be executed when the comment is displayed, potentially revealing sensitive information or performing actions.

Note: No public exploit code is available at this time.

Blue Team (Detection & Prevention)

Detection:

• Monitor comment submissions for unusual shortcode patterns.
• Look for shortcodes that are not part of the site's allowed list.
• Check for unexpected changes in site content or behavior after comment approval.

Prevention:

• Disable the plugin immediately if no patch is available.
• Use a Web Application Firewall (WAF) to block suspicious shortcode patterns in comments.
• Implement a custom filter to strip all shortcodes from comments before display.

Indicators of Compromise (IOCs)

• Network: HTTP POST requests to wp-comments-post.php containing shortcode syntax (e.g., [shortcode]).
• File: Presence of unexpected shortcode tags in the wp_comments database table.
• Behavior: Unauthorized content appearing on the site, such as injected forms or links.
• Logs: WordPress debug logs showing do_shortcode calls with unexpected parameters.

Detection Engineering

YARA Rule

rule azurecurve_shortcode_exploit {
    meta:
        description = "Detects attempts to exploit CVE-2025-2809 via shortcode injection in comments"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-2809"
    strings:
        $shortcode_pattern = /\[[a-zA-Z_]+[^\]]*\]/
        $comment_action = "wp-comments-post.php"
    condition:
        $comment_action and #shortcode_pattern > 0
}

Sigma Rule

title: Azurecurve Shortcode Injection Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP POST requests to WordPress comment submission endpoint containing shortcode patterns
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/wp-comments-post.php'
        cs-uri-query|contains: 'comment'
    keywords:
        - '\['
        - '\]'
    condition: selection and keywords
falsepositives:
    - Legitimate shortcode usage in comments (if allowed by admin)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-2809 - Azurecurve Shortcode Injection Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/wp-comments-post.php"; http_uri; pcre:"/\[[a-zA-Z_]+[^\]]*\]/"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is released.
2. Review and clean any existing comments that may contain malicious shortcodes.
3. Implement a WAF rule to block shortcode patterns in comment submissions.

Long-term Fix:

• Monitor the plugin's official page for updates.
• Consider replacing the plugin with an alternative that properly sanitizes shortcode input.
• Apply the principle of least privilege to shortcode execution.

Valters IT Signature This report was generated by Valters IT Cyber Threat Intelligence Division. For questions, contact intelligence@valters.it.