CVE-2025-5802: Self-Registration Username Disclosure Vulnerability

CVE-2025-5802 Overview

CVE-2025-5802 is a username enumeration vulnerability affecting the self-registration flow in WSO2 products. The registration endpoint accepts user-supplied usernames and returns a distinct error message when a submitted username already exists. This differential response allows unauthenticated attackers to confirm the existence of valid accounts within the system.

The flaw is classified under [CWE-203] Observable Discrepancy. While the vulnerability does not directly compromise credentials or system integrity, disclosed usernames enable follow-on attacks including credential stuffing, brute force, and targeted phishing.

Critical Impact
Unauthenticated network-based attackers can enumerate valid usernames through the self-registration endpoint, providing reconnaissance data for subsequent credential attacks.

Affected Products

WSO2 products exposing the self-registration flow (see vendor advisory for the full product and version list)
Deployments where self-registration is enabled for external users
Identity Server components handling registration requests

Discovery Timeline

2026-09-15 - CVE-2025-5802 published to the National Vulnerability Database
2026-09-15 - Last updated in NVD database

Technical Details for CVE-2025-5802

Vulnerability Analysis

The self-registration flow in affected WSO2 products validates whether a submitted username is already registered and returns an explicit error message when a conflict occurs. This response differs from the response returned for a successful registration or for an unused username. An attacker can therefore submit candidate usernames and infer their existence based on the server's reply.

Username enumeration is a reconnaissance-class weakness. It does not by itself grant access, but it converts an unknown-user brute force problem into a known-user password-guessing problem. Attackers commonly pair the enumerated list with credential stuffing using leaked password corpora or with targeted phishing that references the confirmed account.

Root Cause

The root cause is an observable discrepancy in the registration API response. The system distinguishes the "username already exists" case from other outcomes without normalizing the response. The design fails to treat account existence as sensitive information disclosed to unauthenticated clients.

Attack Vector

Exploitation requires only network access to the registration endpoint. No authentication, privileges, or user interaction are needed. An attacker scripts requests against /self-registration style endpoints, submits candidate usernames, and parses the response body or status code to build a valid account list.

The vulnerability is described in the WSO2 Security Advisory WSO2-2025-4227. Refer to the advisory for endpoint specifics and affected product versions.

Detection Methods for CVE-2025-5802

Indicators of Compromise

High volumes of POST requests to self-registration endpoints originating from a single source IP or narrow IP range
Sequential or dictionary-style username values submitted to the registration API within short time windows
Elevated rate of "username already exists" error responses in application logs relative to successful registrations
Registration traffic from automation user-agents, headless browsers, or known proxy or VPN infrastructure

Detection Strategies

Baseline normal self-registration request rates per source IP and alert on statistical deviations
Correlate registration error responses with follow-on authentication attempts against the same usernames
Inspect WSO2 audit logs for repeated registration attempts using enumerated username patterns such as admin, test, and common first-name lists
Flag registration requests that lack browser session context or bypass the standard UI flow

Monitoring Recommendations

Forward WSO2 Identity Server registration and authentication logs to a centralized SIEM for correlation
Track the ratio of failed to successful registration attempts per source over rolling windows
Monitor downstream login endpoints for credential stuffing that references usernames recently probed at the registration endpoint

How to Mitigate CVE-2025-5802

Immediate Actions Required

Review the WSO2 Security Advisory WSO2-2025-4227 to identify affected product versions in your environment
Apply vendor-supplied patches or version upgrades as specified in the advisory
Disable self-registration if it is not required for your deployment
Enforce CAPTCHA and rate limiting on the registration endpoint to slow automated enumeration

Patch Information

WSO2 has published remediation guidance in security advisory WSO2-2025-4227. Consult the advisory for the fixed versions and WUM update instructions applicable to each affected product. Apply the vendor-recommended updates in non-production environments before promoting to production.

Workarounds

Configure the registration flow to return a generic response for all outcomes, so "username exists" and "username available" cannot be distinguished by the client
Place the registration endpoint behind a Web Application Firewall with rate limiting keyed on source IP and request fingerprint
Require email-based verification before confirming registration, so enumeration cannot be completed synchronously
Restrict access to the self-registration endpoint using network ACLs where the tenant model permits

bash

# Example WAF rate-limit rule (pseudocode)
limit_req_zone $binary_remote_addr zone=selfreg:10m rate=5r/m;

location /accountrecoveryendpoint/register.do {
    limit_req zone=selfreg burst=10 nodelay;
    proxy_pass https://wso2-backend;
}