CVE-2026-106498 in Backstage
Summary
by MITRE • 10/07/2026
Backstage is an open framework for building developer portals. Prior to 3.5.1, 3.6.2, 3.7.2, 3.8.2 and 3.9.1, the @backstage/plugin-catalog-backend package is affected by improper url validation in catalog entity placeholder resolution. An authenticated Backstage user could craft a catalog entity with placeholder directives that reference resources outside the entity's source repository. Under certain configurations, this could allow access to data not intended to be available to the user. This issue is fixed in versions 3.5.1, 3.6.2, 3.7.2, 3.8.2 and 3.9.1.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/07/2026
The vulnerability identified within the Backstage developer portal framework specifically impacts the @backstage/plugin-catalog-backend package in versions prior to 3.5.1, 3.6.2, 3.7.2, 3.8.2, and 3.9.1. This security flaw stems from improper URL validation during the resolution of catalog entity placeholders. Backstage utilizes a system where entities can define dynamic content through placeholder directives, allowing for flexible configuration and integration with external systems. However, in these affected versions, the backend logic responsible for processing these placeholders fails to adequately restrict or validate the target URLs referenced by such directives. This deficiency creates an opportunity for authenticated users to manipulate entity definitions to point towards resources that reside outside of the authorized source repository associated with the catalog entity.
From a technical perspective, this issue represents a classic case of insecure direct object references combined with path traversal-like behaviors in URL parsing logic. When an authenticated user crafts a catalog entity containing placeholder directives, they can specify URLs that target internal services, metadata endpoints, or other sensitive data stores within the organization's infrastructure. Because the backend processes these placeholders without sufficient boundary checks against the intended scope of the entity's source repository, it may fetch and expose content from arbitrary locations on the network. This behavior bypasses standard access controls because the request is initiated by the authenticated user but executed with the privileges of the Backstage service account or internal proxy mechanisms, effectively allowing lateral movement within the trusted environment to retrieve unauthorized data.
The operational impact of this vulnerability is significant for organizations relying on Backstage as their central developer portal. An attacker who has obtained valid credentials can exploit this flaw to exfiltrate sensitive configuration details, proprietary code snippets stored in adjacent repositories, or internal service metadata that should remain isolated from general user access. This compromises the confidentiality and integrity of the organization's software supply chain data. Furthermore, depending on the specific backend integrations configured, such as those connecting to cloud providers or CI/CD pipelines, this could potentially serve as a stepping stone for more severe attacks, including server-side request forgery against internal services that trust requests originating from the Backstage instance.
This vulnerability aligns with CWE-20 Improper Input Validation and CWE-918 Server Side Request Forgery (SSRF). In terms of attack tactics, it corresponds to MITRE ATT&CK technique T1534 Internal Spearphishing or more accurately T1071 Application Layer Protocol if used for data exfiltration via internal channels, but primarily fits the profile of unauthorized access through misconfigured trust relationships. The core issue is a failure in enforcing strict boundaries on user-supplied input within a backend processing context.
To mitigate this risk, organizations must upgrade to Backstage versions 3.5.1, 3.6.2, 3.7.2, 3.8.2, or 3.9.1 and later, where the URL validation logic has been hardened to ensure that placeholder resolutions are strictly confined to the entity's source repository context. Additionally, administrators should review their Backstage configurations to implement network-level controls such as egress filtering for the backend service, ensuring it can only communicate with explicitly whitelisted internal endpoints. Regular auditing of catalog entities and restricting write access to critical catalog definitions further reduces the attack surface by limiting who can introduce potentially malicious placeholder directives into the system.