Summary

Vulnerability: Stored DOM Blind XSS via Backup Management Filename (Persistent Payload Injection)

• Stored Cross-Site Scripting (Blind XSS) via Unsanitized Backup Filename in Backup Management

Description

The application fails to properly sanitize user-controlled input when handling backup uploads and processing backup metadata. An attacker can inject a malicious JavaScript payload into the backup filename via the uploaded xss.sql, which uses SQL functionality to insert the XSS payload server-side.

This stored payload is later rendered unsafely in multiple backup management views without proper output encoding, leading to stored blind cross-site scripting (Blind XSS).

Affected Functionality

• Backup upload functionality
• Backup processing functionality
• Backup storage and retrieval logic

Attack Scenario

• An attacker uploads xss.sql which uses SQL functionality to insert a malicious XSS payload into the backup filename field server-side.
• The application stores this filename without sanitization or encoding.
• The payload persists and executes whenever the backup filename is rendered in affected views.
• The attacker does not see immediate execution, making this a Blind XSS scenario that triggers only when an administrator or privileged user views the backup management panel.

Impact

• Persistent Stored Blind XSS
• Execution of arbitrary JavaScript in victims’ browsers
• Privilege escalation when viewed by administrators or privileged users
• Full administrator account takeover
• Full account takeover across all roles
• Full compromise of the entire application

Endpoints:

• /backend/backup/upload
• /backend/backup/
• /backup/{id}

Steps To Reproduce (POC)

1. Upload xss.sql via the Backup Upload functionality
2. Ensure the SQL executes and inserts an XSS payload into the backup filename field such as: <img src=x onerror=alert(document.domain)>
3. Navigate to the Backup Management panel as an administrator
4. View the backup entry via the administrative panel
5. Notice the XSS payload executing automatically (Blind XSS)

Remediation

• Avoid unsafe DOM manipulation methods: Do not use .html(), innerHTML, or similar sink functions in client-side JavaScript or server-side templating (e.g., PHP). Even when user input flowing into these sinks is not immediately apparent, they can introduce Cross-Site Scripting (XSS) vulnerabilities that an attacker may exploit.

• Apply output encoding: Implement HTML entity encoding on all user-controlled data before rendering it in the browser. This helps neutralize potentially malicious input.

• Implement input sanitization: Ensure that all user-supplied input is properly sanitized before processing or output. Currently, no sanitization mechanisms are in place, which should be addressed as a priority.

• Enforce security headers and cookie attributes:

  • Content Security Policy (CSP): Define and enforce a strict CSP to limit the execution of unauthorized scripts.
  • HttpOnly flag: Set the HttpOnly attribute on session cookies to prevent client-side script access.
  • SameSite attribute: Configure the SameSite cookie attribute to mitigate Cross-Site Request Forgery (CSRF) risks.
  • Secure flag: Ensure all cookies are transmitted only over HTTPS by enabling the Secure attribute.

  These measures collectively reduce the impact of XSS and help prevent escalation paths such as CSRF via XSS.

Ready Video POC:

https://mega.nz/file/eNFXgAAA#IETbPcKwr5vVLqJIAdc3uy4qgcVTgyPb_2HhB4zcwAE