---
id: "CVE-2025-13591"
kind: "vulnerability"
aliases: ["CVE-2025-13591"]
title: "WSO2 Identity Server: login responses reveal which usernames exist"
severity: "medium"
cvss: 5.3
epss: null
exploited: false
status: "open"
category: "other"
products: []
ecosystems: []
tags: ["identity-server", "other", "self-hosted", "wso2"]
not_affected_if: []
published_at: "2026-10-19T17:16:59+00:00"
first_seen_at: "2026-10-23T21:57:18+00:00"
updated_at: "2026-10-25T04:25:01+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-13591", "first_seen_at": "2026-10-23T21:57:18+00:00"}]
---

# WSO2 Identity Server: login responses reveal which usernames exist

The authentication endpoint of WSO2 Identity Server returns responses that differ between existing and non-existing usernames. An attacker can use this to enumerate valid accounts for brute force or phishing.

_Summary, check and fix written by a model from the sources; labelled as such._

## Timeline

- 2026-10-23T21:57:18+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2025-13591

## From the sources

The authentication endpoint of WSO2 Identity Server fails to provide a consistent system response when a username does not exist in the system, allowing attackers to differentiate between valid and invalid usernames. This difference in responses can be leveraged to enumerate existing user accounts.

Successful exploitation enables an attacker to discover valid usernames within the system, significantly increasing the risk of subsequent attacks such as brute force attacks on user credentials, social engineering attacks, and information leakage. The discovered usernames can be used to craft targeted phishing emails or other social engineering campaigns.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_