Listen to this Post
Backstage is an open-source framework used to build developer portals, orchestrating backend services, software templates, and automation tasks. Within Backstage, the Scaffolder plugin enables developers to execute automated tasks such as repository creation, service scaffolding, and CI/CD setup based on predefined templates. These tasks execute sequential actions defined in backend workflows.
CVE-2026-106504 manifests as a sensitive information exposure vulnerability located specifically within the `@backstage/plugin-scaffolder-backend` component. In affected deployments, access control policies are implemented to restrict or deny certain template actions based on permissions. When a task execution invokes a denied action, the backend evaluates the policy and aborts or rejects the step.
However, during this process, input parameters supplied to the denied action—which frequently include sensitive secrets, tokens, or system configurations—are improperly processed during log rendering. Instead of redacting or omitting input values associated with denied or rejected actions, the Scaffolder backend writes the complete payload details into the task execution log stream.
Authenticated users with permissions to create and inspect Scaffolder tasks can view these logs via the task event stream or API endpoints. When a user triggers a workflow containing an action that is denied by policy, the raw parameters passed into that step remain visible in the output log history.
This flaw breaks authorization boundaries by allowing users who lack authorization for specific backend actions to recover sensitive parameter values through execution logs. The vulnerability affects all releases of `@backstage/plugin-scaffolder-backend` prior to version 4.1.0.
DailyCVE Form:
Platform: Backstage Scaffolder Backend
Version: Prior to 4.1.0
Vulnerability: Sensitive Information Exposure
Severity: Moderate Severity
date: October 6 2026
Prediction: Released Version 4.1.0
What Undercode Say:
This vulnerability highlights a critical design oversight in authorization and logging subsystems within developer portal frameworks. When authorization filters reject an action, logging mechanisms must sanitize input parameters regardless of action execution status. Failing to sanitize denied step inputs allows authorization boundaries to be bypassed through log inspection mechanisms.
Exploit: (Educational Purposes!)
Inspect task log output via the Backstage Scaffolder REST API to observe exposed task parameters:
Authenticate and query task event log stream curl -s -H "Authorization: Bearer <AUTH_TOKEN>" \ "https://backstage.example.com/api/scaffolder/v1/tasks/<TASK_ID>/eventstream"
Review returned JSON log events for unredacted parameter inputs attached to denied action steps:
{
"id": 1042,
"taskId": "a1b2c3d4-e5f6-7890-abcd-1234567890ab",
"type": "log",
"body": {
"message": "Action execution denied by policy",
"stepId": "publish-repo",
"status": "failed",
"input": {
"repoUrl": "github.com?repo=service&owner=org",
"accessToken": "ghp_EXAMPLE_EXPOSED_SENSITIVE_TOKEN_12345"
}
}
}
Protection:
Upgrade `@backstage/plugin-scaffolder-backend` to version 4.1.0 or later to ensure proper log sanitization and input suppression on denied actions. Restrict task creation and task log read permissions to trusted users across Backstage templates.
Impact:
Authenticated users with task creation and read access can extract sensitive credentials, tokens, or parameters contained in failed or denied action inputs.
🎯Let’s Practice Exploiting & Learn Patching For Free:
🎓 Live Courses & Certifications:
Join Undercode Academy for Verified Certifications
🚀 Request a Custom Project:
Secure, high-velocity infrastructure and disruptive technological engineering. Contact our engineering team for high-tier development and proprietary systems:
[email protected]
💎 Smart Architecture | 🛡️ Secure by Design | ⭐ Trusted by Thousands
Sources:
Reported By: github.com
Extra Source Hub:
Undercode
