CVE-2026-106500 in plugin-scaffolder-backend
Summary
by MITRE • 10/07/2026
Backstage is an open framework for building developer portals. Prior to 3.3.1, 3.4.1, 4.0.3 and 4.1.0, the @backstage/plugin-scaffolder-backend package is affected by improper task state validation in scaffolder backend. An authenticated user with permission to create and access Scaffolder tasks may, under specific timing and deployment conditions, affect files accessible to the Backstage backend. If backend application files are writable, the confidentiality, integrity, and availability of the backend may be compromised. This issue is fixed in versions 3.3.1, 3.4.1, 4.0.3 and 4.1.0.
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Analysis
by VulDB Data Team • 10/07/2026
The Backstage developer portal framework provides a centralized platform for managing internal developer portals, integrating various tools and services into a unified interface. Within this ecosystem, the scaffolder plugin serves as a critical component responsible for automating software project creation through templated workflows known as tasks. These tasks are executed by the backend service, which manages state transitions such as initialization, execution, completion, and failure. The vulnerability identified in versions prior to 3.3.1, 3.4.1, 4.0.3, and 4.1.0 stems from a flaw in how the scaffolder backend validates task states during these lifecycle transitions. Specifically, the system fails to adequately enforce strict state machine constraints or validate input parameters against expected operational boundaries under certain timing conditions. This lack of rigorous validation allows an authenticated user with permissions to create and access Scaffolder tasks to manipulate the internal state of a running task in unintended ways.
This improper task state validation creates a pathway for unauthorized file system interactions that extend beyond the intended scope of scaffolding operations. When a malicious actor exploits this flaw, they can influence files accessible to the Backstage backend process itself rather than just the isolated workspace designated for new projects. The severity of this impact is heavily dependent on the deployment configuration, particularly whether the backend application directory contains writable files. If the backend binaries or configuration files are modifiable by the user context running the scaffolder service, an attacker can overwrite critical system files. This capability directly undermines the core security principles of confidentiality, integrity, and availability. An adversary could inject malicious code into backend modules to achieve remote code execution, alter configurations to bypass authentication mechanisms for persistent access, or corrupt essential files to cause a denial of service by crashing the application.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation, as the root cause is the failure to sanitize and verify inputs that control state transitions within the scaffolder backend logic. Furthermore, it maps to MITRE ATT&CK techniques related to Defense Evasion and Persistence, specifically T1574 Hijack Execution Flow or T1036 Masquerading if an attacker modifies executable files, as well as T1489 Service Stop for availability impacts. The attack vector typically requires initial authentication, placing it within the scope of authenticated attacks rather than unauthenticated remote code execution, but its potential to escalate privileges and compromise the entire backend infrastructure makes it a high-severity issue in environments where least-privilege principles are not strictly enforced at the operating system level.
Mitigation strategies must focus on both immediate patching and long-term architectural hardening. The primary remediation is to upgrade the @backstage/plugin-scaffolder-backend package to version 3.3.1, 3.4.1, 4.0.3, or 4.1.0, where these state validation flaws have been addressed by developers through stricter input checking and improved isolation of task execution contexts. Beyond patching, organizations should enforce strict file system permissions on the Backstage backend installation directory to ensure that even if an application-level vulnerability is exploited, the operating system prevents modification of critical executable or configuration files. This involves running the backend service under a dedicated user account with minimal privileges, ensuring write access is restricted only to necessary temporary directories and not the root application path. Additionally, implementing robust monitoring for unusual file modifications in backend directories can aid in early detection of exploitation attempts while patches are being deployed across the infrastructure.