CVE-2026-43889 — Outline is a service that allows for collaborative

title: CVE-2026-43889 - Outline API Unauthenticated Share Publication
id: scw-2026-05-11-ai-1
status: experimental
level: critical
description: |
  Detects the specific API endpoint and parameters used in CVE-2026-43889 to exploit the Outline service. An attacker can leverage this by providing both collectionId and documentId with published=false to bypass read access checks and subsequently publish a share that exposes an arbitrary document publicly. This rule specifically targets the vulnerable API call pattern.
author: SCW Feed Engine (AI-generated)
date: 2026-05-11
references:
  - https://shimiscyberworld.com/posts/nvd-CVE-2026-43889/
tags:
  - attack.initial_access
  - attack.t1190
logsource:
    category: webserver
detection:
  selection:
      cs-uri|contains:
          - '/api/shares.create'
      cs-method:
          - 'POST'
      cs-uri-query|contains:
          - 'published=false'
      cs-uri-query|contains:
          - 'collectionId='
      cs-uri-query|contains:
          - 'documentId='
  condition: selection
falsepositives:
  - Legitimate administrative activity

Source: Shimi's Cyber World · License & reuse