CVE-2023-49278: Umbraco CMS brute force exploit can be used to collect valid usernames

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-12-12 · updated 2026-06-17
Weakness: CWE-200

Description

Umbraco is an ASP.NET content management system (CMS). Starting in version 8.0.0 and prior to versions 8.18.10, 10.8.1, and 12.3.4, a brute force exploit can be used to collect valid usernames. Versions 8.18.10, 10.8.1, and 12.3.4 contain a patch for this issue.

Affected products

Umbraco-CMS: from 8.0.0 before 8.18.10; from 10.0.0 before 10.8.1; from 12.0.0 before 12.3.4 — fixed in 10.8.1, 12.3.4, 8.18.10

How to fix

Upgrade to a fixed version: Umbraco-CMS 10.8.1, 12.3.4, 8.18.10. Check the vendor advisory for mitigations.

References

https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-7x74-h8cw-qhxq
https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-7x74-h8cw-qhxq

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