CVE-2026-25138

The WebUI login endpoint returns distinct error messages depending on whether a supplied username exists, allowing unauthenticated attackers to enumerate valid usernames.

Details

When submitting invalid credentials to /ui/login, the WebUI responds with different error messages based on the existence of the provided username (identity). A non-existent username results in an error indicating that no account is associated with the identity, while an existing username with an incorrect password produces a different authentication-related error.

This behavioral difference allows an attacker to distinguish valid usernames from invalid ones by observing the response content.

Proof of Concept

Bogus Login (Non-existent Username "15251087")
Response contains:

Cannot get find any account associated with 15251087 identity.

Bogus Login (Existing Username "root", Wrong Password)
Response contains:

Cannot get auth token. It is possible that the presented identity root is not mapped to any Rucio account root.

The difference in error messages confirms whether a username exists.

Remediation / Mitigation

Return a generic authentication failure message for all login errors, regardless of whether the username exists. Avoid disclosing account or identity existence through error responses. Consider implementing rate limiting or additional login throttling to further reduce abuse.

Reources:

• OWASP Authentication Cheat Sheet - Authentication and Error Messages: https://cheatsheetseries.owasp.org/cheatsheets/Authentication_Cheat_Sheet.html#authentication-and-error-messages

An unauthenticated attacker can enumerate valid usernames, which may be leveraged for targeted password guessing, credential stuffing, or social engineering attacks.

CVE-2026-25138 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (35.8.3, 38.5.4, 39.3.1); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-25138? CVE-2026-25138 is a medium-severity security vulnerability in rucio-webui (pip), affecting versions < 35.8.3. It is fixed in 35.8.3, 38.5.4, 39.3.1.
2. How severe is CVE-2026-25138? CVE-2026-25138 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of rucio-webui are affected by CVE-2026-25138? rucio-webui (pip) versions < 35.8.3 is affected.
4. Is there a fix for CVE-2026-25138? Yes. CVE-2026-25138 is fixed in 35.8.3, 38.5.4, 39.3.1. Upgrade to this version or later.
5. Is CVE-2026-25138 exploitable, and should I be worried? Whether CVE-2026-25138 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-25138 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-25138?
   • Upgrade rucio-webui to 35.8.3 or later
   • Upgrade rucio-webui to 38.5.4 or later
   • Upgrade rucio-webui to 39.3.1 or later