CVE-2025-53250

Executive Summary

CVE-2025-53250 is a Server-Side Request Forgery (SSRF) vulnerability in the Chartbeat WordPress plugin, affecting versions up to and including 2.0.7. This flaw allows an unauthenticated attacker to make the server send crafted HTTP requests to internal or external systems, potentially leading to information disclosure, internal network scanning, or further exploitation. The vulnerability is classified as medium severity (CVSS 6.4) and currently has no known public exploit or patch. Given the plugin's integration with analytics services, this poses a risk to WordPress sites using Chartbeat for real-time audience measurement.

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 and monitor for updates from the vendor. No known supply chain compromise has been reported, but the lack of a patch increases the risk of malicious actors leveraging this flaw.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
• Base Score: 6.4 (Medium)
• Attack Vector: Network (AV:N) – Exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – Vulnerability does not affect other components.
• Confidentiality Impact: Low (C:L) – Limited information disclosure.
• Integrity Impact: Low (I:L) – Limited ability to modify data.
• Availability Impact: None (A:N) – No denial of service.

Threat Level: Medium. While the CVSS score is moderate, SSRF vulnerabilities can be chained with other exploits (e.g., cloud metadata access) to escalate impact.

Deep Dive & Mechanics

The Chartbeat plugin (versions <= 2.0.7) likely implements a server-side proxy or data-fetching mechanism to communicate with Chartbeat's analytics API. The SSRF vulnerability arises when user-supplied input (e.g., a URL parameter or endpoint) is passed directly to a server-side HTTP request function (e.g., wp_remote_get() in WordPress) without proper validation or sanitization.

Root Cause: The plugin fails to restrict the target URL to a whitelist of allowed domains (e.g., *.chartbeat.com). An attacker can manipulate the request to target internal IP addresses (e.g., 169.254.169.254 for cloud metadata), localhost services, or other external systems.

Attack Flow:

1. Attacker identifies a vulnerable endpoint in the plugin that accepts a URL parameter.
2. Attacker crafts a request with a malicious URL pointing to an internal resource (e.g., http://169.254.169.254/latest/meta-data/).
3. The server executes the request and returns the response to the attacker, leaking sensitive data.

Vulnerable vs. Patched Code

Since no patch is available, the following is a hypothetical comparison based on common SSRF mitigation patterns.

Vulnerable Code (PHP):

function chartbeat_fetch_data($url) {
    $response = wp_remote_get($url);
    return wp_remote_retrieve_body($response);
}

Patched Code (Hypothetical):

function chartbeat_fetch_data($url) {
    $allowed_hosts = array('api.chartbeat.com', 'ping.chartbeat.com');
    $parsed_url = parse_url($url);
    if (!in_array($parsed_url['host'], $allowed_hosts)) {
        return new WP_Error('invalid_url', 'URL not allowed');
    }
    $response = wp_remote_get($url);
    return wp_remote_retrieve_body($response);
}

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A WordPress instance with Chartbeat plugin <= 2.0.7 installed and activated.
• Network access to the target server.

Exploitation Steps:

1. Identify the vulnerable endpoint (e.g., /wp-admin/admin-ajax.php?action=chartbeat_proxy&url=...).
2. Craft a request to probe internal services:

   curl "http://target.com/wp-admin/admin-ajax.php?action=chartbeat_proxy&url=http://127.0.0.1:80/"
   

3. Attempt to access cloud metadata (AWS example):

   curl "http://target.com/wp-admin/admin-ajax.php?action=chartbeat_proxy&url=http://169.254.169.254/latest/meta-data/"
   

4. Use the response to extract sensitive information (e.g., IAM credentials, internal network topology).

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

Blue Team (Defensive)

Detection & Response:

• Monitor for outbound HTTP requests to unexpected IP ranges (e.g., RFC 1918 addresses, cloud metadata IPs).
• Deploy a Web Application Firewall (WAF) rule to block requests containing internal IP patterns in URL parameters.
• Implement network segmentation to limit server-side requests to only necessary external domains.

Honeypot Setup:

• Create a fake internal endpoint (e.g., http://127.0.0.1:8080/honeypot) and monitor for access attempts.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Outbound HTTP requests to 169.254.169.254, 127.0.0.1, or other internal IPs.
  • Requests to unusual ports (e.g., :6379 for Redis, :3306 for MySQL).
• File IOCs:
  • Modified chartbeat.php or related plugin files.
  • Suspicious entries in WordPress debug logs (e.g., wp-content/debug.log).
• Log IOCs:
  • Apache/Nginx access logs showing action=chartbeat_proxy with non-standard URLs.
  • PHP error logs indicating failed wp_remote_get() calls to blocked IPs.

Detection Engineering

YARA Rule

rule CVE_2025_53250_SSRF_Chartbeat {
    meta:
        description = "Detects SSRF exploitation attempts against Chartbeat plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-53250"
    strings:
        $url_param = "action=chartbeat_proxy" nocase
        $internal_ip = /(127\.0\.0\.1|10\.\d{1,3}\.\d{1,3}\.\d{1,3}|172\.(1[6-9]|2[0-9]|3[01])\.\d{1,3}\.\d{1,3}|192\.168\.\d{1,3}\.\d{1,3}|169\.254\.\d{1,3}\.\d{1,3})/
    condition:
        $url_param and $internal_ip
}

Sigma Rule

title: CVE-2025-53250 SSRF Exploitation via Chartbeat Plugin
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP requests to internal IPs via Chartbeat plugin proxy
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-uri-query|contains: "action=chartbeat_proxy"
        cs-uri-query|contains|any:
            - "127.0.0.1"
            - "10."
            - "172.16."
            - "172.17."
            - "172.18."
            - "172.19."
            - "172.20."
            - "172.21."
            - "172.22."
            - "172.23."
            - "172.24."
            - "172.25."
            - "172.26."
            - "172.27."
            - "172.28."
            - "172.29."
            - "172.30."
            - "172.31."
            - "192.168."
            - "169.254."
    condition: selection
falsepositives:
    - Legitimate internal monitoring tools
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-53250 - Chartbeat SSRF Exploitation Attempt";
    flow:to_server;
    content:"action=chartbeat_proxy";
    http_uri;
    pcre:"/(127\.0\.0\.1|10\.\d{1,3}\.\d{1,3}\.\d{1,3}|172\.(1[6-9]|2[0-9]|3[01])\.\d{1,3}\.\d{1,3}|192\.168\.\d{1,3}\.\d{1,3}|169\.254\.\d{1,3}\.\d{1,3})/";
    classtype:attempted-recon;
    sid:10000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin if not critical to operations until a patch is released.
2. Implement a WAF rule to block requests containing internal IP patterns in URL parameters.
3. Restrict outbound traffic from the web server using firewall rules (e.g., allow only *.chartbeat.com).

Long-Term Fix:

• Apply vendor patch when available (monitor Chartbeat's official channels).
• Replace the plugin with an alternative analytics solution if patching is not feasible.

Workaround:

• Modify the plugin code to add URL whitelisting (see patched code example above). Note: This will be overwritten on plugin updates.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Analyst