CVE-2025-63951

Executive Summary

CVE-2025-63951 is a critical insecure deserialization vulnerability identified in the MiczFlor RPi-Jukebox-RFID project, specifically within the rss-mp3.php script. The vulnerability allows a remote, unauthenticated attacker to inject arbitrary PHP objects via the rss GET parameter, which is passed directly to the unserialize() function without any validation or sanitization. This can lead to application errors or a denial of service (DoS) condition. The project is a PHP-based jukebox system for Raspberry Pi, and the vulnerability affects all versions up to and including commit 4b2334f0ae0e87c0568876fc41c48c38aa9a7014 (dated 2025-10-07). No official patch has been released, and the vendor's patch status is marked as UNKNOWN/UNPATCHED.

Supply Chain & Package Security

This vulnerability is not related to a package manager (NPM, PyPI, Go, Ruby) but is a direct code-level issue in the PHP application. The project is self-contained and does not rely on external package dependencies for the vulnerable component. However, the use of unserialize() on user-supplied data is a well-known insecure practice in PHP, and the lack of input validation represents a significant supply chain risk for any deployment of this software.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Base Score: 7.5)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
• Attack Vector (AV): Network (N) – The vulnerability can be exploited remotely over the network.
• Attack Complexity (AC): Low (L) – No special conditions are required for exploitation.
• Privileges Required (PR): None (N) – No authentication is needed.
• User Interaction (UI): None (N) – The victim does not need to perform any action.
• Scope (S): Unchanged (U) – The impact is confined to the vulnerable component.
• Confidentiality (C): None (N) – No data is exposed.
• Integrity (I): None (N) – No data is modified.
• Availability (A): High (H) – The vulnerability can cause a denial of service, making the application unavailable.

Threat Level: High. The ease of exploitation (no authentication, low complexity) combined with the potential for DoS makes this a significant threat. While the CVSS score is listed as 0.0 in the NVD data, the calculated base score is 7.5 (High) based on the vector.

Deep Dive & Mechanics

The vulnerability resides in the rss-mp3.php script of the RPi-Jukebox-RFID project. The script is designed to handle RSS feed data, but it improperly processes the rss GET parameter. The core issue is the direct use of PHP's unserialize() function on user-supplied input without any validation.

How it works:

1. An attacker sends an HTTP GET request to the vulnerable endpoint, e.g., http://target/rss-mp3.php?rss=<malicious_payload>.
2. The rss parameter value is passed directly to unserialize().
3. PHP's unserialize() attempts to convert the serialized string back into a PHP object. If the attacker crafts a malicious serialized object (e.g., using PHP Object Injection techniques), the application will instantiate that object.
4. During the object's lifecycle (e.g., __wakeup(), __destruct() magic methods), the attacker can trigger arbitrary code execution or cause errors that lead to a denial of service.

Why it's dangerous:

• No Authentication: The endpoint is accessible without any login.
• No Input Validation: The rss parameter is not sanitized or validated before being passed to unserialize().
• PHP Object Injection: An attacker can leverage PHP's magic methods to execute arbitrary code, read/write files, or cause the application to crash.

Example of a malicious serialized payload (conceptual):

O:10:"MaliciousClass":1:{s:4:"data";s:10:"malicious";}

This payload, when passed to unserialize(), would instantiate the MaliciousClass object, potentially triggering its __wakeup() or __destruct() methods.

Vulnerable vs. Patched Code

Vulnerable Code (from rss-mp3.php):

<?php
// Vulnerable: Direct unserialize of user input
$rss_data = $_GET['rss'];
$obj = unserialize($rss_data);
// ... rest of the script
?>

Patched Code (Hypothetical):

<?php
// Patched: Validate and sanitize input before unserialize
$rss_data = $_GET['rss'];
if (is_serialized($rss_data) && is_allowed_class($rss_data)) {
    $obj = unserialize($rss_data);
} else {
    // Handle error or reject request
    http_response_code(400);
    echo "Invalid input";
    exit;
}
// ... rest of the script
?>

Note: The ideal fix is to avoid using unserialize() on user-supplied data altogether. Instead, use JSON or other safe serialization formats. The patched code above is a minimal example; a proper fix would involve using json_decode() or implementing a whitelist of allowed classes.

Exploitation & Lab Setup

Red Team (Exploitation)

Lab Setup:

1. Install the vulnerable version of RPi-Jukebox-RFID on a Raspberry Pi or local server (e.g., using Docker or a PHP development environment).
2. Ensure the rss-mp3.php script is accessible via a web server (e.g., Apache or Nginx).

Exploitation Steps:

1. Craft a malicious serialized PHP object that triggers a denial of service (e.g., by causing an infinite loop or memory exhaustion).
2. Send the payload via a GET request:

   curl "http://target/rss-mp3.php?rss=O:10:\"MaliciousClass\":1:{s:4:\"data\";s:10:\"malicious\";}"
   

3. Observe the application crash or become unresponsive.

Example DoS Payload (using PHP's __wakeup magic method):

<?php
class DoS {
    public function __wakeup() {
        while (true) {
            // Infinite loop to cause DoS
        }
    }
}
$payload = serialize(new DoS());
echo urlencode($payload);
?>

This payload, when passed to unserialize(), will cause an infinite loop, consuming CPU resources and leading to a denial of service.

Blue Team (Defense & Detection)

Detection:

• Monitor web server logs for unusual GET requests to rss-mp3.php with long or suspicious rss parameters.
• Use WAF rules to block requests containing serialized PHP objects (e.g., patterns like O:\d+:").
• Implement input validation to reject non-serialized data.

Mitigation:

• Apply the hypothetical patch above or replace unserialize() with json_decode().
• Restrict access to rss-mp3.php using IP whitelisting or authentication.
• Use a Web Application Firewall (WAF) to filter malicious payloads.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP GET requests to /rss-mp3.php with a rss parameter containing serialized PHP objects (e.g., O:10:"ClassName":...).
  • Unusual patterns in the rss parameter, such as base64-encoded strings or long, non-standard data.
• System IOCs:
  • High CPU usage or application crashes on the server.
  • PHP error logs showing unserialize() errors or unexpected class instantiation.
• File IOCs:
  • Presence of unexpected PHP files or modified scripts in the web root.

Detection Engineering

YARA Rule

rule CVE_2025_63951_Insecure_Deserialization {
    meta:
        description = "Detects attempts to exploit CVE-2025-63951 via insecure deserialization in rss-mp3.php"
        author = "Valters IT"
        date = "2025-10-07"
        reference = "CVE-2025-63951"
    strings:
        $serialized_pattern = /O:\d+:"[^"]+":\d+:\{/
        $url_pattern = /rss-mp3\.php\?rss=/
    condition:
        $url_pattern and $serialized_pattern
}

Sigma Rule

title: CVE-2025-63951 Insecure Deserialization Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects HTTP requests targeting rss-mp3.php with serialized PHP objects
author: Valters IT
date: 2025-10-07
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-uri-query|contains: "rss-mp3.php?rss="
        cs-uri-query|re: "O:\\d+:\"[^\"]+\":\\d+:\\{"
    condition: selection
falsepositives:
    - Legitimate use of serialized data (unlikely)
level: high

Suricata Rule

alert http any any -> any any (
    msg:"CVE-2025-63951 - Insecure Deserialization in rss-mp3.php";
    flow:to_server,established;
    content:"rss-mp3.php"; http_uri;
    content:"rss="; http_uri;
    pcre:"/O:\d+:\"[^\"]+\":\d+:\{/";
    sid:10000001;
    rev:1;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the vulnerable endpoint: If possible, remove or disable rss-mp3.php until a patch is applied.
2. Apply input validation: Implement strict validation on the rss parameter to reject any non-serialized data or use a whitelist of allowed classes.
3. Use a WAF: Deploy a Web Application Firewall with rules to block serialized PHP objects.

Long-term Fix:

• Replace unserialize() with json_decode() or another safe serialization method.
• Update to a patched version of RPi-Jukebox-RFID once available.
• Conduct a security audit of the entire codebase for similar vulnerabilities.

Workaround:

• Restrict access to rss-mp3.php via .htaccess or Nginx configuration to only allow trusted IP addresses.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert