Umbraco: Delivery API leaks protected (Public Access) content through Content Picker / Multi-Node Tree Picker expansion

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. Prior to 13.15.1, 17.5.3, and 18.0.2, the Content Delivery API applies member and Public Access checks to the directly requested node but not to referenced nodes serialized through Content Picker or Multi-Node Tree Picker properties, including pickers nested in Block List, Block Grid, or Rich Text Editor blocks. When DeliveryApi:PublicAccess is enabled, an anonymous caller can retrieve a protected node's name, route, and id through an unprotected referencing node and use ?expand to retrieve full property values. When the Delivery API is instead gated by the organization-wide API key, a key holder can still bypass per-node Public Access through the same expansion path. The same RequestContextOutputExpansionStrategyV2 and ElementOnlyOutputExpansionStrategy path also bypasses allowed or disallowed content-type alias restrictions for referenced content. Direct requests for the protected node still return 401, and no integrity or availability impact is established. This issue is fixed in versions 13.15.1, 17.5.3, and 18.0.2.

Source published

17 Sep 2026 15:44:24 UTC

Source modified

17 Sep 2026 17:23:18 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Umbraco is an ASP.NET CMS. Prior to 13.15.1, 17.5.3, and 18.0.2, the Content Delivery API applies member and Public Access checks to the directly requested node but not to referenced nodes serialized through Content Picker or Multi-Node Tree Picker properties, including pickers nested in Block List, Block Grid, or Rich Text Editor blocks. When DeliveryApi:PublicAccess is enabled, an anonymous caller can retrieve a protected node's name, route, and id through an unprotected referencing node and use ?expand to retrieve full property values. When the Delivery API is instead gated by the organization-wide API key, a key holder can still bypass per-node Public Access through the same expansion path. The same RequestContextOutputExpansionStrategyV2 and ElementOnlyOutputExpansionStrategy path also bypasses allowed or disallowed content-type alias restrictions for referenced content. Direct requests for the protected node still return 401, and no integrity or availability impact is established. This issue is fixed in versions 13.15.1, 17.5.3, and 18.0.2.

Source published

Sep 17, 2026, 3:44:24 PM (timezone not stated)

Source modified

Sep 17, 2026, 5:23:18 PM (timezone not stated)

Observed here

11 Nov 2026 16:00:21 UTC

Source terms

ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Umbraco is an ASP.NET CMS. Prior to 13.15.1, 17.5.3, and 18.0.2, the Content Delivery API applies member and Public Access checks to the directly requested node but not to referenced nodes serialized through Content Picker or Multi-Node Tree Picker properties, including pickers nested in Block List, Block Grid, or Rich Text Editor blocks. When DeliveryApi:PublicAccess is enabled, an anonymous caller can retrieve a protected node's name, route, and id through an unprotected referencing node and use ?expand to retrieve full property values. When the Delivery API is instead gated by the organization-wide API key, a key holder can still bypass per-node Public Access through the same expansion path. The same RequestContextOutputExpansionStrategyV2 and ElementOnlyOutputExpansionStrategy path also bypasses allowed or disallowed content-type alias restrictions for referenced content. Direct requests for the protected node still return 401, and no integrity or availability impact is established. This issue is fixed in versions 13.15.1, 17.5.3, and 18.0.2.

Source published

17 Sep 2026 16:17:41 UTC

Source modified

30 Sep 2026 17:51:56 UTC

Observed here

25 Oct 2026 15:18:51 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

The Content Delivery API enforces member / Public Access protection only at the controller layer, against the node that is directly requested. When a public (unprotected) node references a protected node through a Content Picker or Multi-Node Tree Picker (including those nested inside Block List, Block Grid, or Rich Text Editor blocks), the Delivery API expands and serializes the protected node with no access check applied. Similarly, configuration based restrictions based on aliases of allowed or disallowed content types are by-passed for referenced content items that are retrieved via property expansion. As a result, an anonymous / unauthorized caller can retrieve a protected node's: - Name, route, and id — always, even without expansion, and - Full property values — when the request uses ?expand on the picker property. A direct request for the same protected node correctly returns 401 Unauthorized, which makes the leak easy to miss: the protection appears to work, but is bypassed via reference expansion. ### Impact Confidential, member-gated content (e.g. pricing, internal documents, gated articles) referenced by any publicly readable node is disclosed to unauthenticated clients. No write/integrity or availability impact. Highest impact when the Delivery API is publicly readable (DeliveryApi:PublicAccess: true). Still exploitable, at reduced severity, when the Delivery API is gated by the org-wide API key (the key holder still bypasses per-node Public Access). ### Patches 13.15.1, 17.5.3, 18.0.2 ### References https://docs.umbraco.com/umbraco-cms/develop-with-umbraco/headless-and-apis/content-delivery-api

Source published

17 Sep 2026 16:29:46 UTC

Source modified

17 Sep 2026 16:45:08 UTC

Observed here

23 Oct 2026 16:01:25 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Publisher rating · HIGH