CVE-2025-67585

Executive Summary

CVE-2025-67585 is an open redirect vulnerability in the Flexmls® IDX WordPress plugin, affecting versions through 3.15.7. This flaw allows an unauthenticated attacker to craft a URL that, when clicked by a logged-in administrator or site visitor, redirects them to an arbitrary external domain. The vulnerability is classified as a Phishing attack vector (MITRE T1566) with a CVSS score of 4.7 (Medium). No public proof-of-concept code or patch is currently available. The plugin is part of the WordPress ecosystem, and exploitation could lead to credential harvesting or malware distribution via trusted site redirects.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Users should verify the integrity of their plugin files against the official source and monitor for updates from the vendor. No known supply chain compromise has been reported.

CVSS Breakdown & Threat Level

• CVSS Score: 4.7 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
• Attack Vector (AV): Network – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low – No special conditions required.
• Privileges Required (PR): None – No authentication needed.
• User Interaction (UI): Required – The victim must click a crafted link.
• Scope (S): Changed – The redirect can lead to a different security domain.
• Confidentiality (C): Low – Potential for credential theft.
• Integrity (I): Low – The redirect can modify user perception.
• Availability (A): None – No impact on service availability.

Threat Level: Medium. While the CVSS score is moderate, the phishing potential and lack of a patch elevate the risk for WordPress sites using this plugin.

Deep Dive & Mechanics

The vulnerability resides in the flexmls-idx plugin’s URL handling logic. The plugin likely processes a redirect or return parameter in its authentication or search functionality without proper validation. An attacker can inject a malicious URL (e.g., https://evil.com) into this parameter. When a user clicks a crafted link like:

https://victim-site.com/wp-content/plugins/flexmls-idx/?redirect=https://evil.com

The plugin’s PHP code performs a header("Location: " . $_GET['redirect']) or similar redirect without checking if the target domain is allowed. This allows the attacker to phish users by presenting a legitimate-looking URL that ultimately leads to a malicious site.

Root Cause: The plugin fails to validate the redirect target against a whitelist of allowed domains or uses a weak validation that can be bypassed (e.g., checking only for the presence of the site’s domain in the URL).

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code pattern is inferred. A typical vulnerable implementation:

// Vulnerable code (flexmls-idx <= 3.15.7)
$redirect_url = $_GET['redirect'];
if (!empty($redirect_url)) {
    header("Location: " . $redirect_url);
    exit;
}

A patched version would validate the redirect target:

// Patched code (hypothetical)
$redirect_url = $_GET['redirect'];
$allowed_hosts = array('example.com', 'www.example.com');
$parsed_url = parse_url($redirect_url);
if (!empty($redirect_url) && in_array($parsed_url['host'], $allowed_hosts)) {
    header("Location: " . $redirect_url);
    exit;
} else {
    // Redirect to a safe default
    header("Location: /");
    exit;
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• A WordPress site with Flexmls® IDX plugin version <= 3.15.7.
• A controlled external server (e.g., evil.com) to receive redirected traffic.

Exploitation Steps:

1. Identify a vulnerable endpoint that accepts a redirect parameter. Common parameters include redirect, return, url, or next.
2. Craft a phishing link:

   https://victim-site.com/?flexmls-idx-redirect=https://evil.com/phishing-page
   

3. Send the link to a target via email or social engineering.
4. When the target clicks, they are redirected to evil.com, which can host a fake login page to harvest credentials.

Note: No public exploit code is available; this is a conceptual demonstration.

Blue Team

Detection & Prevention:

• Monitor web server logs for unusual redirect parameters pointing to external domains.
• Implement a Web Application Firewall (WAF) rule to block requests with redirect parameters containing external URLs.
• Use browser-based protections like X-Content-Type-Options: nosniff and Content-Security-Policy to mitigate phishing impact.

Lab Setup:

• Deploy a vulnerable WordPress instance with Flexmls IDX 3.15.7 in a sandboxed environment.
• Use a tool like Burp Suite to intercept and modify redirect parameters.
• Verify the redirect behavior by sending crafted requests.

Indicators of Compromise (IOCs)

• URL Patterns: Requests containing redirect=, return=, or url= parameters pointing to external domains.
• Log Entries: HTTP 302 responses with Location headers pointing to non-whitelisted domains.
• Network Traffic: Outbound connections to known phishing or malicious domains shortly after a redirect.
• File Hashes: (If available) Modified plugin files with altered redirect logic.

Detection Engineering

YARA Rule

rule CVE_2025_67585_Flexmls_Open_Redirect {
    meta:
        description = "Detects open redirect patterns in Flexmls IDX plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-67585"
    strings:
        $redirect_param = /[?&](redirect|return|url)=https?:\/\// nocase
        $flexmls_path = /wp-content\/plugins\/flexmls-idx/
    condition:
        $flexmls_path and $redirect_param
}

Sigma Rule

title: CVE-2025-67585 Flexmls IDX Open Redirect
id: 8a3f7c2e-5d1b-4a9f-8c6e-2b1d3f4a5c6d
status: experimental
description: Detects open redirect attempts targeting Flexmls IDX plugin
author: Valters IT
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-uri-query|contains: 
            - 'redirect=http'
            - 'return=http'
            - 'url=http'
        cs-uri-stem|contains: '/wp-content/plugins/flexmls-idx/'
    condition: selection
falsepositives:
    - Legitimate redirects to whitelisted domains (if any)
level: medium

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-67585 Flexmls IDX Open Redirect Attempt";
    flow:to_server,established;
    content:"/wp-content/plugins/flexmls-idx/"; http_uri;
    content:"redirect="; http_uri; nocase;
    pcre:"/redirect=https?:\/\//Ui";
    classtype:attempted-recon;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin if it is not critical to business operations.
2. Apply a virtual patch using a WAF to block requests with redirect parameters containing external URLs.
3. Monitor logs for any signs of exploitation.

Long-Term Fix:

• The vendor (Flexmls) must release a patched version that validates redirect targets against a whitelist.
• Until a patch is available, consider replacing the plugin with an alternative IDX solution.

Workaround:

• Add the following rule to .htaccess (Apache) or equivalent Nginx config to block external redirects:

  RewriteCond %{QUERY_STRING} (redirect|return|url)=https?:// [NC]
  RewriteRule ^wp-content/plugins/flexmls-idx/ - [F,L]
  

Valters IT
Securing Digital Frontiers