Ampache issue4: Web Share Create / External Share Arbitrary Target

Vulnerability call chain

1.1 Summary

Ampache has a missing authorization vulnerability: Web Share Create / External Share Arbitrary Target. The attacker can create a public share for an object they cannot otherwise access

• Attack precondition: - For create: a logged-in web user can obtain a valid add_share form token
• Security impact: The attacker can create a public share for an object they cannot otherwise access

1.2 Exploit path

• GET /share.php?action=show_create&type={type}&id={id} to obtain form context / token

1.3 Key code evidence

1. share.php

Evidence location: share.php
2. public/share.php

Evidence location: public/share.php

3. Root Cause Analysis

Root Cause 1: Missing server-side authorization on the vulnerable operation.

The endpoint accepts user-controlled authorization-sensitive identifiers or fields, but the write/read path does not prove that the current caller may operate on the target object.

Root Cause 2: Missing object-scope or grant-bound validation.

The implementation relies on endpoint access, UI filtering, or object existence checks instead of enforcing target ownership, tenant boundary, role ceiling, or grantable-resource constraints at the service layer.

4. Recommended fix

Before creating a share in CreateAction and ExternalShareAction, load the target object and enforce the same target authorization helper recommended for API share_create

5. Verification after fix

• Unauthorized callers receive HTTP 403 or equivalent rejection.
• Out-of-scope target identifiers are rejected before database writes or sensitive reads.
• Role, permission, tenant, organization, ownership, or grant-bound ceilings are enforced server-side.
• Direct HTTP requests are rejected even when front-end controls are hidden.