CVE-2026-69197 in Umbraco-CMS
Summary
by MITRE • 09/17/2026
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.
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified in Umbraco CMS affects the Content Delivery API's handling of access control checks for referenced content nodes. Specifically, prior to versions 13.15.1, 17.5.3, and 18.0.2, the system applies member and Public Access validations exclusively to the node directly requested by an incoming HTTP request. However, this security enforcement is not extended to child or referenced nodes that are serialized through properties such as Content Picker or Multi-Node Tree Picker. This oversight persists even when these pickers are nested within complex structures like Block List, Block Grid, or Rich Text Editor blocks. The core technical flaw lies in the RequestContextOutputExpansionStrategyV2 and ElementOnlyOutputExpansionStrategy implementations, which fail to recursively validate access permissions for all nodes included in the response payload during serialization.
When the DeliveryApi:PublicAccess configuration is enabled, an anonymous user can exploit this logic gap by requesting a node that has no public access restrictions but contains references to protected content. By utilizing the expand query parameter, the attacker forces the API to serialize and return full property values of these referenced nodes. Although direct requests for the protected node itself correctly return a 401 Unauthorized response, the indirect retrieval via referencing nodes allows the disclosure of sensitive metadata including the name, route, and identifier of the restricted content. This constitutes an information leakage vulnerability where access control policies are effectively bypassed through relationship traversal rather than direct resource access.
The impact extends beyond anonymous users to authenticated API consumers as well. When the Content Delivery API is secured by a global organization-wide API key, holders of this key can similarly bypass per-node Public Access restrictions using the same expansion mechanism. This indicates that the vulnerability affects both public-facing content exposure and internal data integrity regarding access control granularity. Furthermore, the flaw also circumvents allowed or disallowed content-type alias restrictions for referenced content, allowing users to retrieve types of content they should not be permitted to view based on their assigned permissions or role definitions.
From a security classification perspective, this issue aligns with CWE-284 Improper Access Control and CWE-601 URL Redirection to Untrusted Destination if the route information is leveraged for further attacks, though primarily it represents an authorization bypass through indirect object reference handling failures. In terms of MITRE ATT&CK mapping, this behavior corresponds to T1530 Data from Cloud Storage Object Discovery or more accurately T1078 Valid Accounts combined with data exfiltration techniques where the attacker uses legitimate API access patterns to harvest restricted information without triggering standard authentication blocks for individual resources.
The operational impact is primarily limited to confidentiality breaches involving metadata and property values of protected content, as there is no established integrity compromise or availability disruption. Attackers cannot modify system state or cause service denial through this vector alone. However, the exposure of internal routing structures and node identifiers can facilitate further reconnaissance efforts against the CMS instance. The vulnerability does not allow for remote code execution or direct database manipulation but serves as a significant weakness in data segregation strategies within multi-tenant or role-based access control environments.
Mitigation requires upgrading Umbraco to version 13.15.1, 17.5.3, or 18.0.2 where the serialization logic has been corrected to enforce access checks on all referenced nodes regardless of their nesting depth within pickers or block editors. Organizations unable to immediately upgrade should implement a Web Application Firewall rule set that monitors for unusual patterns in expand query parameters targeting Content Delivery API endpoints and restricts deep expansion requests from untrusted sources. Additionally, reviewing the public access configuration settings to ensure minimal exposure of sensitive content types is recommended as a compensating control until patching can be performed.