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

> Unauthenticated attackers can enumerate valid usernames via distinct login error messages in the Rucio WebUI.

- **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:** Yes
- **Published:** 25 Feb 2026
- **Updated:** 26 Feb 2026
- **Also known as:** GHSA-38wq-6q2w-hcf9, PYSEC-2026-3053

## What is CVE-2026-25138?

CVE-2026-25138 is a medium-severity vulnerability in rucio, published on 25 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-204 (Observable Response Discrepancy)

## Which versions are affected by CVE-2026-25138?

7 open source packages ship an affected version, including rucio-webui. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `rucio-webui` | PyPI | All versions | 35.8.3, 38.5.4, 39.3.1 |
| `rucio-webui` | PyPI | All versions | 35.8.3 |
| `rucio-webui` | PyPI | All versions | 35.8.3 |
| `rucio-webui` | PyPI | From 36.0.0rc1 | 38.5.4 |
| `rucio-webui` | PyPI | From 36.0.0rc1 | 38.5.4 |
| `rucio-webui` | PyPI | From 39.0.0rc1 | 39.3.1 |
| `rucio-webui` | PyPI | From 39.0.0rc1 | 39.3.1 |

Products: Cern Rucio.

## How do I fix CVE-2026-25138?

Upgrade rucio-webui to a fixed version for your release line: 35.8.3, 38.5.4 or 39.3.1.

## Is CVE-2026-25138 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-25138 exists.

## Other vulnerabilities in rucio

- [CVE-2026-29080](https://insights.sbomify.com/CVE-2026-29080/): Rucio SQL Injection in FilterEngine Oracle JSON Path via DID Search API (critical 9.4)
- [CVE-2026-29090](https://insights.sbomify.com/CVE-2026-29090/): Rucio SQL injection in postgres_meta DID search path compromises PostgreSQL metadata database (critical 9.0)
- [CVE-2026-25136](https://insights.sbomify.com/CVE-2026-25136/): Rucio WebUI has a Reflected Cross-site Scripting Vulnerability (high 8.1)
- [CVE-2026-25733](https://insights.sbomify.com/CVE-2026-25733/): Rucio WebUI Vulnerable to Stored Cross-site Scripting (XSS) through Custom Rule Function (high 7.3)
- [CVE-2026-25734](https://insights.sbomify.com/CVE-2026-25734/): Rucio WebUI has Stored Cross-site Scripting (XSS) in RSE Metadata (medium 6.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-25138 and fix it if it is affected.

What it is: CVE-2026-25138 is a medium-severity vulnerability in rucio, published on 25 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-25138 exists.

Affected packages and fixed versions:
- rucio-webui (PyPI): affected all versions; fixed in 35.8.3, 38.5.4, 39.3.1
- rucio-webui (PyPI): affected all versions; fixed in 35.8.3
- rucio-webui (PyPI): affected all versions; fixed in 35.8.3
- rucio-webui (PyPI): affected from 36.0.0rc1; fixed in 38.5.4
- rucio-webui (PyPI): affected from 36.0.0rc1; fixed in 38.5.4
- rucio-webui (PyPI): affected from 39.0.0rc1; fixed in 39.3.1
- rucio-webui (PyPI): affected from 39.0.0rc1; fixed in 39.3.1

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-2026-25138/ (Markdown: https://insights.sbomify.com/CVE-2026-25138/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-25138
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-25138
- OSV: https://osv.dev/vulnerability/CVE-2026-25138

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-25138/
Summaries are generated and may contain mistakes; the official description above is the record.