Password reset flows are notoriously difficult to secure. They are often publicly accessible, require minimal inputs (usually just an email), and serve as a gateway for Account Takeover (ATO) attacks via credential stuffing or enumeration.

While rate limiting is a standard defense, it fails against distributed botnets utilizing residential proxies. A rate limit of 5 requests per IP is ineffective when an attacker rotates through 10,000 distinct IPs. To secure this vector without degrading User Experience (UX) with aggressive CAPTCHAs, security engineers must implement real-time IP reputation analysis.

The Attack Vector

Attackers target password reset endpoints for two primary reasons:

User Enumeration: Determining if an email exists in the database based on the server's response time or error message.
Reset Token Interception: In scenarios where tokens are weak or the email account is compromised, the reset flow completes the ATO.

Sophisticated attacks route traffic through datacenter proxies, VPNs, or compromised residential nodes to mask their identity. By integrating IP intelligence, you can segregate traffic based on network risk profiles before processing the request.

Implementation Strategy

The defense logic should operate at the application middleware layer, prior to database queries or email dispatch.

Ingress: Capture the client IP.
Enrichment: Query IPASIS to retrieve metadata (ASN type, proxy status, threat score).
Decision Engine:
- Allow: Residential/Mobile IPs with clean history.
- Challenge: VPNs/Public Proxies (Require CAPTCHA or Email Magic Link).
- Block: Tor nodes, Hosting providers (AWS/DigitalOcean), or IPs with high abuse scores.

Integration Logic

Below is a Python implementation using a simplified Flask context. This logic integrates the IPASIS API to analyze the request origin before triggering the reset flow.

import requests
from flask import request, jsonify

IPASIS_API_KEY = 'your_api_key'

def check_ip_reputation(ip_address):
    try:
        # Query IPASIS for real-time intelligence
        url = f"https://api.ipasis.com/json/{ip_address}?key={IPASIS_API_KEY}"
        response = requests.get(url, timeout=2.0)
        data = response.json()
        
        return data
    except Exception as e:
        # Fail open or closed depending on security posture
        return None

def handle_password_reset():
    client_ip = request.remote_addr
    ip_data = check_ip_reputation(client_ip)

    if ip_data:
        # CRITICAL: Block requests from Tor exit nodes
        if ip_data.get('is_tor', False):
            return jsonify({"error": "Request blocked due to high-risk network."}), 403

        # HIGH RISK: Block datacenter IPs (unlikely to be valid users resetting passwords)
        if ip_data.get('is_datacenter', False):
             return jsonify({"error": "Please perform this action from a residential network."}), 403

        # MEDIUM RISK: If VPN/Proxy detected, force a CAPTCHA challenge
        if ip_data.get('is_proxy', False) or ip_data.get('is_vpn', False):
            if not validate_captcha(request.form.get('captcha_token')):
                return jsonify({"error": "Security check required."}), 400

    # LOW RISK: Proceed with standard reset flow
    send_reset_email(request.form.get('email'))
    return jsonify({"message": "If that email exists, a link has been sent."})

Analyzing ASN Context

Simply checking for proxies is often insufficient. Analyzing the Autonomous System Number (ASN) provides context regarding the "intent" of the traffic.

ISP/Residential ASNs (e.g., Comcast, Verizon): Generally low risk. High volume from a single residential IP should still trigger rate limiting.
Hosting ASNs (e.g., Hetzner, OVH): Legitimate users rarely reset passwords from a headless server environment. These should be treated with extreme suspicion or blocked entirely for this specific endpoint.

Frequently Asked Questions

Q: Will blocking VPNs lock out legitimate users? A: It can. Therefore, we recommend a "Challenge" response rather than a hard "Block" for VPNs. Trigger a reCAPTCHA or require a 2FA code if the IP is identified as a commercial VPN service.

Q: What is the latency impact of an IP reputation check? A: The IPASIS API is optimized for real-time decision-making with sub-100ms response times. This is negligible compared to the time required to send an SMTP email.

Q: Can attackers spoof their IP? A: While attackers can spoof headers (like X-Forwarded-For), the TCP connection must be established with a valid IP. Ensure your application reads the actual socket connection IP, or strictly trusts the X-Forwarded-For header only from your internal load balancers.

Secure Your Endpoints with IPASIS

Don't wait for a credential stuffing attack to compromise your user base. Integrate IPASIS today to detect proxies, VPNs, and bad actors at the network edge.

Get your free API key at IPASIS.com and start securing your authentication flows immediately.

Mitigating Account Takeovers: Securing Password Reset Flows with IP Reputation