SSRF Vulnerability in private-ip Package 

Overview

A critical Server-Side Request Forgery (SSRF) vulnerability (CVE-2025-8020) has been discovered in all versions of the private-ip npm package. The vulnerability allows attackers to bypass IP validation checks by supplying a multicast IP address (224.0.0.0/4), which is not properly filtered by the package. This flaw can lead to unauthorized internal network requests, potentially exposing sensitive systems.

• CVSS Score: 8.8 (High)
• Vulnerability Type: SSRF
• Affected Package: private-ip (all versions)
• Disclosure Date: 2025-07-23
• Discovered By: Snyk

Technical Details 

Root Cause

The private-ip package is designed to check whether a given IP address falls within private (non-routable) ranges (e.g., 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16). However, it fails to account for multicast IP addresses (224.0.0.0/4), which are used for group communication in networks.

An attacker can exploit this oversight by providing:

• A hostname that resolves to a multicast IP.
• A direct multicast IP (e.g., 224.0.0.1).

Since the package incorrectly classifies multicast IPs as "private," applications relying on private-ip for security checks may allow malicious requests to internal services.

Exploitation Scenario

1. Attack via Hostname Resolution

Suppose an application uses private-ip to validate user-supplied URLs before fetching internal resources:

const privateIp = require('private-ip');

function fetchInternalResource(url) {
  const hostname = new URL(url).hostname;

  if (privateIp(hostname)) {
    console.log("Blocked: Private IP range detected.");
  } else {
    // Fetch the resource (vulnerable to SSRF)
    console.log("Fetching:", url);
  }
}

// Attacker-controlled domain resolving to 224.0.0.1
fetchInternalResource("http://attacker-multicast.example.com/api/sensitive");

Exploit Flow:

1. The attacker registers a domain (attacker-multicast.example.com) pointing to 224.0.0.1.
2. The application checks the hostname using private-ip, which incorrectly allows it.
3. The server makes an internal request to the multicast address, potentially interacting with local services.

2. Direct Multicast IP Bypass

If an application directly accepts IP addresses:

const privateIp = require('private-ip');

function fetchResource(ip) {
  if (privateIp(ip)) {
    console.log("Blocked: Private IP detected.");
  } else {
    console.log("Allowed:", ip);
  }
}

// Attacker sends a multicast IP (224.0.0.1)
fetchResource("224.0.0.1"); // Returns "Allowed" due to the bug

Impact:

• An attacker could scan internal services by leveraging multicast packets.
• In some cases, multicast traffic could be routed to unintended internal systems.

Mitigation & Fixes

Immediate Workarounds

1. Manually Validate IP Ranges:

   • Use an allowlist of trusted domains/IPs instead of relying solely on private-ip.
   • Explicitly block multicast (224.0.0.0/4) and other non-private ranges.

   function isSafeIP(ip) {
    return !ip.startsWith("224.") && privateIp(ip);
   }

2. Disable Affected Features:

   • Temporarily disable functionality that processes user-supplied URLs/IPs.

Permanent Fix

• Update private-ip:
• The maintainers should release a patched version that includes multicast IP checks.
• Developers should upgrade as soon as a fix is available.

Conclusion

CVE-2025-8020 highlights the risks of incomplete IP validation in security-sensitive applications. Organizations using private-ip should apply mitigations immediately and monitor for patches. SSRF vulnerabilities can lead to severe breaches, making proactive fixes essential.