Umbraco Vulnerable to Improper File Access and Credential Exposure through Dictionary Import Functionality

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

Umbraco is an ASP.NET CMS. Due to unsafe handling and deletion of temporary files in versions 10.0.0 through 13.12.0, during the dictionary upload process an attacker with access to the backoffice can trigger predictable requests to temporary file paths. The application’s error responses (HTTP 500 when a file exists, 404 when it does not) allow the attacker to enumerate the existence of arbitrary files on the server’s filesystem. This vulnerability does not allow reading or writing file contents. In certain configurations, incomplete clean-up of temporary upload files may additionally expose the NTLM hash of the Windows account running the Umbraco application. This issue is fixed in version 13.12.1.

Source published

9 Dec 2025 20:09:27 UTC

Source modified

12 Dec 2025 20:33:09 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 4.9 CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N

Umbraco is an ASP.NET CMS. Due to unsafe handling and deletion of temporary files in versions 10.0.0 through 13.12.0, during the dictionary upload process an attacker with access to the backoffice can trigger predictable requests to temporary file paths. The application’s error responses (HTTP 500 when a file exists, 404 when it does not) allow the attacker to enumerate the existence of arbitrary files on the server’s filesystem. This vulnerability does not allow reading or writing file contents. In certain configurations, incomplete clean-up of temporary upload files may additionally expose the NTLM hash of the Windows account running the Umbraco application. This issue is fixed in version 13.12.1.

Source published

Dec 9, 2025, 8:09:27 PM (timezone not stated)

Source modified

Dec 12, 2025, 8:33:09 PM (timezone not stated)

Observed here

9 Nov 2026 04:09:39 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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EUVD CVSS 3.1 · 4.9 CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N

Umbraco is an ASP.NET CMS. Due to unsafe handling and deletion of temporary files in versions 10.0.0 through 13.12.0, during the dictionary upload process an attacker with access to the backoffice can trigger predictable requests to temporary file paths. The application’s error responses (HTTP 500 when a file exists, 404 when it does not) allow the attacker to enumerate the existence of arbitrary files on the server’s filesystem. This vulnerability does not allow reading or writing file contents. In certain configurations, incomplete clean-up of temporary upload files may additionally expose the NTLM hash of the Windows account running the Umbraco application. This issue is fixed in version 13.12.1.

Source published

9 Dec 2025 20:15:55 UTC

Source modified

14 Oct 2026 21:10:00 UTC

Observed here

25 Oct 2026 03:17:36 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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CVSS 3.1 · [email protected] · Secondary · 4.9 CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N

### Impact Due to unsafe handling and deletion of temporary files during the dictionary upload process, an attacker with access to the backoffice can trigger predictable requests to temporary file paths. The application’s error responses (HTTP 500 when a file exists, 404 when it does not) allow the attacker to enumerate the existence of arbitrary files on the server’s filesystem. This vulnerability does not allow reading or writing file contents. In certain configurations, incomplete clean-up of temporary upload files may additionally expose the NTLM hash of the Windows account running the Umbraco application. The direct impact of this vulnerability is therefore limited to confidentiality, which is reflected in its CVSS base score of 4.9 While the CVSS Base Score captures only the immediate effect, the practical risk varies significantly based on hosting environment and identity configuration. Umbraco Cloud sites run under low-privilege, isolated Azure App Service worker identities, which mitigates the impact of any credential exposure. In contrast, self-hosted deployments could run Umbraco using privileged local or domain accounts. If such an account’s NTLM hash is disclosed, an attacker may be able to: - Perform NTLM relay attacks - Crack the hash offline to recover the underlying password - Authenticate as the compromised identity - Access internal systems trusted by that identity - Move laterally within the network - Potentially escalate to full domain compromise in weakly segmented environments These outcomes are not part of the CVSS base score, which only rates the immediate confidentiality impact, but represent realistic downstream consequences for installations using elevated or widely-trusted service accounts. Self-hosted environments running Umbraco under privileged identities are therefore at significantly higher risk. Vulnerability found and reported by Tomasz Holeksa at Pentest Limited ### Patches The issue has been patched in 13.12.1. ### Workarounds The issue can only be exploited by authorized backoffice accounts with access to the "Translations" section.

Source published

9 Dec 2025 17:12:18 UTC

Source modified

9 Dec 2025 22:30:47 UTC

Observed here

23 Oct 2026 16:01:25 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N

Publisher rating · MODERATE