CVE-2025-48953: Umbraco Vulnerable to By-Pass of Configured Allowed Extensions for File Uploads

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-06-03 · updated 2026-06-17
Weakness: CWE-434

Description

Umbraco is an ASP.NET content management system (CMS). Starting in version 14.0.0 and prior to versions 15.4.2 and 16.0.0, it's possible to upload a file that doesn't adhere with the configured allowable file extensions via a manipulated API request. The issue is patched in versions 15.4.2 and 16.0.0. No known workarounds are available.

Affected products

Umbraco-CMS: from 14.0.0 before 15.4.2 — fixed in 15.4.2

How to fix

Upgrade to a fixed version: Umbraco-CMS 15.4.2. Check the vendor advisory for mitigations.

References

https://github.com/umbraco/Umbraco-CMS/commit/d920e93d1ee29dc3301697e444f53e8cd5db3cf9
https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-fr6r-p8hv-x3c4

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