title: CVE-2021-41773 Exploitation Attempt
id: 3007fec6-e761-4319-91af-e32e20ac43f5
status: experimental
description: Detects exploitation of flaw in path normalization in Apache HTTP server 2.4.49. 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. This issue is known to be exploited in the wild. This issue only affects Apache 2.4.49 and not earlier versions.
author: daffainfo, Florian Roth
date: 2021/10/05
modified: 2021/10/06
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2021-41773
    - https://github.com/apache/httpd/commit/e150697086e70c552b2588f369f2d17815cb1782
    - https://twitter.com/ptswarm/status/1445376079548624899
    - https://twitter.com/h4x0r_dz/status/1445401960371429381
    - https://github.com/projectdiscovery/nuclei-templates/blob/master/cves/2021/CVE-2021-41773.yaml
    - https://twitter.com/bl4sty/status/1445462677824761878
logsource:
  category: webserver
detection:
    selection:
        c-uri|contains: 
            - '/cgi-bin/.%2e/'
            - '/icons/.%2e/'
            - '/cgi-bin/.%%32%65/'
            - '/icons/.%%32%65/'
            - '/cgi-bin/.%%%25%33'
            - '/icons/.%%%25%33'
    selection_success:
        sc-status: 
            - 200
            - 301    
    condition: selection and selection_success
falsepositives:
    - Unknown
tags:
    - attack.initial_access
    - attack.t1190
level: high