{"id":"CVE-2026-42205","aliases":["GHSA-qc5p-3mg5-9fh8"],"url":"https://o3.security/vulnerability/CVE-2026-42205","summary":"Avo: Broken Access Control: Unauthorized Execution of Arbitrary Action Classes Across Resources","details":"### Summary\n\nA critical Broken Access Control vulnerability was identified in the `ActionsController` of the Avo framework (v3.x). Due to insecure action lookup logic, an authenticated user can execute any Action class (descendants of `Avo::BaseAction`) on any resource, even if the action is not registered for that specific resource. This leads to Privilege Escalation and unauthorized data manipulation across the entire application.\n\n### Details\n\nThe vulnerability exists in the `action_class` method within `app/controllers/avo/actions_controller.rb`.\n\n#### Vulnerable Code\n\n```ruby\ndef action_class\n  # It searches through ALL descendants of BaseAction without resource validation\n  Avo::BaseAction.descendants.find do |action|\n    action.to_s == params[:action_id]\n  end\nend\n```\n\nThe controller identifies the action class to execute solely based on the `params[:action_id]` by searching through all `BaseAction` descendants. It fails to verify whether the requested action is actually permitted or registered for the resource context specified in the request URL (e.g., `/admin/resources/posts/actions`).\n\nConsequently, an attacker can invoke sensitive actions (e.g., `Avo::Actions::ToggleAdmin`) through an unrelated resource endpoint (e.g., `Post`), bypassing the intended resource-action mapping.\n\n### Impact\n\nThis flaw results in significant security risks:\n\n- **Privilege Escalation:** An authenticated user with low privileges can execute administrative actions (like toggling admin roles) to escalate their own or others' permissions.\n- **Unauthorized Operations:** Actions designed for restricted resources can be triggered against any record ID in the database.\n- **Data Integrity Compromise:** Attackers can perform unauthorized destructive operations (e.g., Delete, Archive, or Update) on records they should not have access to.\n\n### Proof of Concept (PoC)\n\n**Steps to Reproduce:**\n\n01. Log in to the Avo admin panel with limited permissions.\n02. Identify a target record ID (e.g., User ID: 1) and a sensitive action class (e.g., `Avo::Actions::ToggleAdmin`).\n03. Send a POST request to a resource endpoint where the target action is not registered:\n    - **URL:** `POST /admin/resources/posts/actions`\n    - **Payload:** `action_id=Avo::Actions::ToggleAdmin&fields[avo_resource_ids]=1`\n04. The server executes the `ToggleAdmin` logic on User 1, even though the request was made through the `posts` resource context.\n\n**PoC Script Snippet:**\n\n```python\n# Simulating the unauthorized action execution\ndata = {\n    'action_id': 'Avo::Actions::ToggleAdmin',\n    'fields[avo_resource_ids]': '1', # Target Record ID\n    'authenticity_token': csrf_token\n}\nresponse = session.post(f\"{BASE_URL}/admin/resources/posts/actions\", data=data)\n```\n\n### Remediation\n\nRestrict the action lookup to only those actions explicitly registered for the current resource context:\n\n```ruby\ndef action_class\n  # Validate that the action is registered for the current resource\n  @resource.get_actions.find do |action|\n    action.to_s == params[:action_id]\n  end\nend\n```\n\n### Discoverer\n\nIllunight","published":"2026-05-08T21:26:44.743Z","modified":"2026-08-12T03:51:45.677476355Z","cvss":{"score":8.8,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"},"epss":{"score":0.00295,"percentile":0.2189,"asOf":"2026-08-14"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"RubyGems","name":"avo","fixedVersion":"3.31.2"}],"fix":null,"references":[{"type":"WEB","url":"https://github.com/avo-hq/avo/releases/tag/v3.31.2"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/42xxx/CVE-2026-42205.json"},{"type":"ADVISORY","url":"https://github.com/avo-hq/avo/security/advisories/GHSA-qc5p-3mg5-9fh8"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-42205"},{"type":"PACKAGE","url":"https://github.com/avo-hq/avo"},{"type":"WEB","url":"https://github.com/rubysec/ruby-advisory-db/blob/master/gems/avo/CVE-2026-42205.yml"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:45.677476355Z"}}