Executive Summary

Prosper, a major peer-to-peer lending platform, has suffered a large-scale data breach impacting an estimated 17.6 million user accounts. The compromised data, which includes personally identifiable information (PII) such as full names, email addresses, and phone numbers, has been verified and added to the Have I Been Pwned database. This incident creates a significant and immediate risk for affected individuals, who are now prime targets for sophisticated phishing attacks, identity theft, and other forms of fraud. All Prosper users should assume they are affected and take immediate steps to secure their accounts and remain vigilant against suspicious communications.

Threat Overview

On October 17, 2025, the 'Have I Been Pwned' service announced the addition of the Prosper breach data, following confirmation from the company of unauthorized access to its systems. While the specific threat actor and attack vector have not been disclosed, the scale of the breach indicates a significant failure in data protection controls. The exfiltrated data provides malicious actors with a rich dataset to craft highly convincing and personalized attacks.

The primary threats to the 17.6 million affected users are:

• Targeted Phishing: Attackers can use the stolen names, emails, and phone numbers to create spear-phishing campaigns that appear to be legitimate communications from Prosper or other financial institutions.
• SIM Swapping and Account Takeover: Phone numbers can be used to conduct SIM swapping attacks, potentially bypassing SMS-based two-factor authentication to take over user accounts.
• Identity Theft: The combination of PII can be used to open fraudulent accounts or commit other forms of identity theft.
• Credential Stuffing: While passwords were not reported as compromised, attackers will likely use the list of email addresses to attempt credential stuffing attacks against other services.

Technical Analysis

The breach involves the exfiltration of a large database of user PII. The attack likely involved an adversary gaining access to a production database or a backup containing customer information. Common attack paths for this type of breach include:

• T1190 - Exploit Public-Facing Application: Exploiting a vulnerability in a web application connected to the database.
• T1078 - Valid Accounts: Using compromised credentials of an employee or service account with access to the data.
• T1530 - Data from Cloud Storage Object: Accessing a misconfigured or poorly secured cloud storage bucket (e.g., AWS S3) containing the user data.

Once access was gained, the threat actor would have used a technique like T1020 - Automated Exfiltration to transfer the large volume of data out of Prosper's environment.

Impact Assessment

The business impact on Prosper includes significant reputational damage, potential regulatory fines for data protection failures, and costs associated with incident response and customer support. For the 17.6 million affected individuals, the impact is direct and personal. The breach erodes trust and exposes them to a long-term risk of financial fraud and identity theft. The inclusion of the data in 'Have I Been Pwned' is a double-edged sword: it provides easy notification for users but also confirms the data's availability to a wider audience of malicious actors.

Detection & Response (for Affected Users)

• Check 'Have I Been Pwned': Visit haveibeenpwned.com and enter your email address to confirm if you were part of this breach.
• Monitor Communications: Be extremely vigilant for unsolicited emails, text messages, or phone calls claiming to be from Prosper or other financial institutions. Do not click on links or provide personal information.
• Review Account Activity: Log into your Prosper account and any linked financial accounts to review for suspicious activity.

Mitigation (for Affected Users)

1. Change Your Password: Immediately change your password for your Prosper account. Use a strong, unique password.
2. Enable Multi-Factor Authentication (D3-MFA: Multi-factor Authentication): Enable MFA on your Prosper account and any other online service that offers it, especially financial accounts. Prioritize app-based authenticators (like Google Authenticator or Authy) over SMS-based 2FA.
3. Place Fraud Alerts: Consider placing a fraud alert or credit freeze with the major credit bureaus (Equifax, Experian, TransUnion) to prevent unauthorized accounts from being opened in your name.
4. Be Skeptical: Treat any communication regarding this breach with skepticism. Verify information directly on Prosper's official website, not through links in an email.