Vulnerability-Lookup

CVE-2026-55518 (GCVE-0-2026-55518)

Vulnerability from cvelistv5 – Published: 2026-07-17 20:51 – Updated: 2026-07-20 15:20

Title

Avo: Missing Authorization in Avo Association Attach Endpoint Allows Unauthorized Relationship Manipulation and Privilege Escalation

Summary

Avo is a framework to create admin panels for Ruby on Rails apps. Prior to 3.32.1 and 4.0.0.beta.51, Avo's association attach workflow checks attach_<association>? in the UI and GET /resources/:resource/:id/:related/new path, but the actual write endpoint, POST /resources/:resource/:id/:related, does not run the same authorization check before mutating the association through Avo::AssociationsController#create. An authenticated low-privileged Avo user can bypass hidden or disabled attach controls and directly attach related records to a parent record by sending a crafted POST request, which can lead to privilege escalation and cross-tenant data exposure where associations represent authorization-bearing relationships. This issue is fixed in versions 3.32.1 and 4.0.0.beta.51.

Severity

9.6 (Critical)


                        
                          CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N

SSVC

Exploitation: poc Automatable: no Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-07-20 15:18 UTC

CWE

CWE-639 - Authorization Bypass Through User-Controlled Key
CWE-862 - Missing Authorization
CWE-863 - Incorrect Authorization

Assigner

GitHub_M mitre root

References

4 references

URL	Tags
https://github.com/avo-hq/avo/security/advisories…	x_refsource_CONFIRM
https://github.com/avo-hq/avo/pull/4568	x_refsource_MISC
https://github.com/avo-hq/avo/commit/995928e586fd…	x_refsource_MISC
https://github.com/avo-hq/avo/releases/tag/v3.32.1	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
avo-hq	avo	Affected: >= 4.0.0.beta.1, < 4.0.0.beta.51 Affected: < 3.32.1	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-55518

Vulnerability from fkie_nvd - Published: 2026-07-17 21:17 - Updated: 2026-07-23 17:58

Severity

9.6 (Critical) - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/avo-hq/avo/commit/995928e586fd1788dd496bd51c4dbe4a79cb2b9c
	security-advisories@github.com	https://github.com/avo-hq/avo/pull/4568
	security-advisories@github.com	https://github.com/avo-hq/avo/releases/tag/v3.32.1
	security-advisories@github.com	https://github.com/avo-hq/avo/security/advisories/GHSA-8fq9-273g-6mrg
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/avo-hq/avo/security/advisories/GHSA-8fq9-273g-6mrg

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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          "product": "avo",
          "vendor": "avo-hq",
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}

GHSA-8FQ9-273G-6MRG

Vulnerability from github – Published: 2026-06-17 18:49 – Updated: 2026-07-18 17:22

Summary

Avo: Missing Authorization in Avo Association Attach Endpoint Allows Unauthorized Relationship Manipulation and Privilege Escalation

Details

Summary

A critical missing authorization flaw exists in Avo's association attach workflow. The UI and GET /resources/:resource/:id/:related/new path can check attach_<association>?, but the actual write endpoint, POST /resources/:resource/:id/:related, does not run the same authorization check before mutating the association.

As a result, an authenticated low-privileged Avo user can bypass hidden/disabled attach controls and directly attach related records to a parent record by sending a crafted POST request. In applications where associations represent teams, tenants, roles, projects, users, memberships, ownership, or other authorization-bearing relationships, this can lead to privilege escalation and cross-tenant data exposure.

Details

The association attach route writes relationships through Avo::AssociationsController#create:

# config/routes.rb
post "/:resource_name/:id/:related_name", to: "associations#create", as: "associations_create"

The controller registers an attach authorization callback only for new, not for create:

# app/controllers/avo/associations_controller.rb
before_action :set_attachment_record, only: [:create, :destroy]
before_action :authorize_index_action, only: :index
before_action :authorize_attach_action, only: :new
before_action :authorize_detach_action, only: :destroy

The new action is only the form-rendering step. The actual mutation happens in create:

def create
  if create_association
    create_success_action
  else
    create_fail_action
  end
end

create_association then attaches the attacker-supplied related record to the parent:

def create_association
  association_name = BaseResource.valid_association_name(@record, association_from_params)

  perform_action_and_record_errors do
    if through_reflection? && additional_params.present?
      new_join_record.save
    elsif has_many_reflection? || through_reflection?
      @record.send(association_name) << @attachment_record
    else
      @record.send(:"#{association_name}=", @attachment_record)
      @record.save!
    end
  end
end

The only attach-specific authorization helper is:

def authorize_attach_action
  authorize_if_defined "attach_#{@field.id}?"
end

Because this helper is bound only to new, a policy that denies attach_users?, attach_teams?, attach_roles?, or similar methods blocks the UI/form path but does not protect the write path.

This is inconsistent with the detach path, which does authorize the mutating destroy action:

before_action :authorize_detach_action, only: :destroy

The bug is especially dangerous because Avo already treats association authorization as an access-control boundary in UI components:

# lib/avo/concerns/checks_assoc_authorization.rb
method_name = :"#{policy_method}_#{association_name}?".to_sym

if service.has_method?(method_name, raise_exception: false)
  service.authorize_action(method_name, record:, raise_exception: false)
else
  !Avo.configuration.explicit_authorization
end

However, server-side enforcement is missing on the actual attach POST endpoint.

Proof of Concept

Prerequisites:

A Rails application mounts Avo, for example at /admin.
Avo authorization is enabled.
A low-privileged user can authenticate to Avo.
A parent record and a related record are both reachable by ID.
The relevant policy denies attaching the relationship, for example:

def attach_users?
  false
end

Example target scenario:

Parent resource: projects
Parent ID: 1
Related association: users
Related user ID to attach: 42
Expected policy: low-privileged users must not be able to attach users to projects.

The UI/form request may be blocked:

GET /admin/resources/projects/1/users/new

But the direct write endpoint can still be invoked:

POST /admin/resources/projects/1/users
Content-Type: application/x-www-form-urlencoded

authenticity_token=<CSRF>&fields[related_id]=42

Run the attached PoC:

python poc_avo_association_attach_bypass.py \
  --base-url http://localhost:3000 \
  --avo-root /admin \
  --cookie "_app_session=<LOW_PRIVILEGED_SESSION_COOKIE>" \
  --parent-resource projects \
  --parent-id 1 \
  --related-name users \
  --related-id 42 \
  --check-new

If GET /new is forbidden or redirected but the direct POST succeeds, the authorization bypass is confirmed.

To perform the actual attach:

python poc_avo_association_attach_bypass.py \
  --base-url http://localhost:3000 \
  --avo-root /admin \
  --cookie "_app_session=<LOW_PRIVILEGED_SESSION_COOKIE>" \
  --parent-resource projects \
  --parent-id 1 \
  --related-name users \
  --related-id 42 \
  --confirm-attach

Expected vulnerable result:

The low-privileged user can attach the related record despite attach_<association>? being denied.
The parent record now includes the related record.

Impact

This vulnerability allows unauthorized relationship manipulation through Avo.

Depending on the affected association, the impact can include:

Privilege escalation by attaching a user to an admin group, privileged project, tenant, organization, role, or membership record.
Cross-tenant data exposure when tenant/user/project membership determines record visibility.
Integrity loss by changing ownership, assignment, access-control relationships, or business workflow state.
Policy bypass even when Avo UI controls correctly hide the attach button or deny the attach form.

Recommended Fix

Enforce attach authorization on the mutating endpoint.

At minimum:

before_action :authorize_attach_action, only: [:new, :create]

Additionally:

Authorize against the parent record and the selected related record before writing the relationship.
Ensure create fails closed when attach_<association>? is missing and explicit_authorization is enabled.
Add regression tests that directly POST to /resources/:resource_name/:id/:related_name while attach_<association>? returns false.
Verify has_many, has_one, has_many :through, and has_and_belongs_to_many association paths all enforce the same server-side authorization.

Severity

9.6 (Critical)


                  
                    CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.32.0"
      },
      "package": {
        "ecosystem": "RubyGems",
        "name": "avo"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.32.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "RubyGems",
        "name": "avo"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.0.0.beta.1"
            },
            {
              "fixed": "4.0.0.beta.51"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-55518"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-639",
      "CWE-862",
      "CWE-863"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-17T18:49:11Z",
    "nvd_published_at": "2026-07-17T21:17:09Z",
    "severity": "CRITICAL"
  },
  "details": "## Summary\n\nA critical missing authorization flaw exists in Avo\u0027s association attach workflow. The UI and `GET /resources/:resource/:id/:related/new` path can check `attach_\u003cassociation\u003e?`, but the actual write endpoint, `POST /resources/:resource/:id/:related`, does not run the same authorization check before mutating the association.\n\nAs a result, an authenticated low-privileged Avo user can bypass hidden/disabled attach controls and directly attach related records to a parent record by sending a crafted POST request. In applications where associations represent teams, tenants, roles, projects, users, memberships, ownership, or other authorization-bearing relationships, this can lead to privilege escalation and cross-tenant data exposure.\n\n## Details\n\nThe association attach route writes relationships through `Avo::AssociationsController#create`:\n\n```ruby\n# config/routes.rb\npost \"/:resource_name/:id/:related_name\", to: \"associations#create\", as: \"associations_create\"\n```\n\nThe controller registers an attach authorization callback only for `new`, not for `create`:\n\n```ruby\n# app/controllers/avo/associations_controller.rb\nbefore_action :set_attachment_record, only: [:create, :destroy]\nbefore_action :authorize_index_action, only: :index\nbefore_action :authorize_attach_action, only: :new\nbefore_action :authorize_detach_action, only: :destroy\n```\n\nThe `new` action is only the form-rendering step. The actual mutation happens in `create`:\n\n```ruby\ndef create\n  if create_association\n    create_success_action\n  else\n    create_fail_action\n  end\nend\n```\n\n`create_association` then attaches the attacker-supplied related record to the parent:\n\n```ruby\ndef create_association\n  association_name = BaseResource.valid_association_name(@record, association_from_params)\n\n  perform_action_and_record_errors do\n    if through_reflection? \u0026\u0026 additional_params.present?\n      new_join_record.save\n    elsif has_many_reflection? || through_reflection?\n      @record.send(association_name) \u003c\u003c @attachment_record\n    else\n      @record.send(:\"#{association_name}=\", @attachment_record)\n      @record.save!\n    end\n  end\nend\n```\n\nThe only attach-specific authorization helper is:\n\n```ruby\ndef authorize_attach_action\n  authorize_if_defined \"attach_#{@field.id}?\"\nend\n```\n\nBecause this helper is bound only to `new`, a policy that denies `attach_users?`, `attach_teams?`, `attach_roles?`, or similar methods blocks the UI/form path but does not protect the write path.\n\nThis is inconsistent with the detach path, which does authorize the mutating `destroy` action:\n\n```ruby\nbefore_action :authorize_detach_action, only: :destroy\n```\n\nThe bug is especially dangerous because Avo already treats association authorization as an access-control boundary in UI components:\n\n```ruby\n# lib/avo/concerns/checks_assoc_authorization.rb\nmethod_name = :\"#{policy_method}_#{association_name}?\".to_sym\n\nif service.has_method?(method_name, raise_exception: false)\n  service.authorize_action(method_name, record:, raise_exception: false)\nelse\n  !Avo.configuration.explicit_authorization\nend\n```\n\nHowever, server-side enforcement is missing on the actual attach POST endpoint.\n\n## Proof of Concept\n\nPrerequisites:\n\n1. A Rails application mounts Avo, for example at `/admin`.\n2. Avo authorization is enabled.\n3. A low-privileged user can authenticate to Avo.\n4. A parent record and a related record are both reachable by ID.\n5. The relevant policy denies attaching the relationship, for example:\n\n```ruby\ndef attach_users?\n  false\nend\n```\n\nExample target scenario:\n\n- Parent resource: `projects`\n- Parent ID: `1`\n- Related association: `users`\n- Related user ID to attach: `42`\n- Expected policy: low-privileged users must not be able to attach users to projects.\n\nThe UI/form request may be blocked:\n\n```http\nGET /admin/resources/projects/1/users/new\n```\n\nBut the direct write endpoint can still be invoked:\n\n```http\nPOST /admin/resources/projects/1/users\nContent-Type: application/x-www-form-urlencoded\n\nauthenticity_token=\u003cCSRF\u003e\u0026fields[related_id]=42\n```\n\nRun the attached PoC:\n\n```bash\npython poc_avo_association_attach_bypass.py \\\n  --base-url http://localhost:3000 \\\n  --avo-root /admin \\\n  --cookie \"_app_session=\u003cLOW_PRIVILEGED_SESSION_COOKIE\u003e\" \\\n  --parent-resource projects \\\n  --parent-id 1 \\\n  --related-name users \\\n  --related-id 42 \\\n  --check-new\n```\n\nIf `GET /new` is forbidden or redirected but the direct POST succeeds, the authorization bypass is confirmed.\n\nTo perform the actual attach:\n\n```bash\npython poc_avo_association_attach_bypass.py \\\n  --base-url http://localhost:3000 \\\n  --avo-root /admin \\\n  --cookie \"_app_session=\u003cLOW_PRIVILEGED_SESSION_COOKIE\u003e\" \\\n  --parent-resource projects \\\n  --parent-id 1 \\\n  --related-name users \\\n  --related-id 42 \\\n  --confirm-attach\n```\n\nExpected vulnerable result:\n\n- The low-privileged user can attach the related record despite `attach_\u003cassociation\u003e?` being denied.\n- The parent record now includes the related record.\n\n## Impact\n\nThis vulnerability allows unauthorized relationship manipulation through Avo.\n\nDepending on the affected association, the impact can include:\n\n- Privilege escalation by attaching a user to an admin group, privileged project, tenant, organization, role, or membership record.\n- Cross-tenant data exposure when tenant/user/project membership determines record visibility.\n- Integrity loss by changing ownership, assignment, access-control relationships, or business workflow state.\n- Policy bypass even when Avo UI controls correctly hide the attach button or deny the attach form.\n\n## Recommended Fix\n\nEnforce attach authorization on the mutating endpoint.\n\nAt minimum:\n\n```ruby\nbefore_action :authorize_attach_action, only: [:new, :create]\n```\n\nAdditionally:\n\n1. Authorize against the parent record and the selected related record before writing the relationship.\n2. Ensure `create` fails closed when `attach_\u003cassociation\u003e?` is missing and `explicit_authorization` is enabled.\n3. Add regression tests that directly POST to `/resources/:resource_name/:id/:related_name` while `attach_\u003cassociation\u003e?` returns `false`.\n4. Verify `has_many`, `has_one`, `has_many :through`, and `has_and_belongs_to_many` association paths all enforce the same server-side authorization.",
  "id": "GHSA-8fq9-273g-6mrg",
  "modified": "2026-07-18T17:22:29Z",
  "published": "2026-06-17T18:49:11Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/avo-hq/avo/security/advisories/GHSA-8fq9-273g-6mrg"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-55518"
    },
    {
      "type": "WEB",
      "url": "https://github.com/avo-hq/avo/pull/4568"
    },
    {
      "type": "WEB",
      "url": "https://github.com/avo-hq/avo/commit/995928e586fd1788dd496bd51c4dbe4a79cb2b9c"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/avo-hq/avo"
    },
    {
      "type": "WEB",
      "url": "https://github.com/avo-hq/avo/releases/tag/v3.32.1"
    },
    {
      "type": "WEB",
      "url": "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/avo/CVE-2026-55518.yml"
    },
    {
      "type": "WEB",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-55518"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Avo: Missing Authorization in Avo Association Attach Endpoint Allows Unauthorized Relationship Manipulation and Privilege Escalation"
}

Sightings

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Nomenclature

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Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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Action not permitted

CVE-2026-55518 (GCVE-0-2026-55518)

FKIE_CVE-2026-55518

GHSA-8FQ9-273G-6MRG

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