# CVE-2025-13591: Username Enumeration via Authentication Endpoint in WSO2 Identity Server Allows User Account Discovery

> Attackers can enumerate valid usernames via inconsistent authentication responses, facilitating targeted attacks like phishing or brute force.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 19 Oct 2026
- **Updated:** 20 Oct 2026
- **Also known as:** GHSA-9j2j-6wwh-jwf6

## What is CVE-2025-13591?

CVE-2025-13591 is a medium-severity vulnerability in WSO2 Email OTP Authenticator, published on 19 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-203 (Observable Discrepancy)

## Which versions are affected by CVE-2025-13591?


## How do I fix CVE-2025-13591?

No fix has been published for CVE-2025-13591 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-13591 being exploited?

There is no known exploitation of CVE-2025-13591 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-13591 and fix it if it is affected.

What it is: CVE-2025-13591 is a medium-severity vulnerability in WSO2 Email OTP Authenticator, published on 19 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-13591 in the wild and no public exploit code.

Affected product: WSO2 Email OTP Authenticator. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-13591/ (Markdown: https://insights.sbomify.com/CVE-2025-13591/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-13591
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-13591
- OSV: https://osv.dev/vulnerability/CVE-2025-13591

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From sbomify Insights: https://insights.sbomify.com/CVE-2025-13591/
Summaries are generated and may contain mistakes; the official description above is the record.