CVE-2021-41773 Exploitation Attempt

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.

Query · sigma

selection:
  cs-uri-query|contains:
  - /cgi-bin/.%2e/
  - /icons/.%2e/
  - /cgi-bin/.%%32%65/
  - /icons/.%%32%65/
  - /cgi-bin/.%%%25%33
  - /icons/.%%%25%33
  sc-status:
  - 200
  - 301
condition: selection

Known false positives

  • Unknown
Raw source CVE-2021-41773 Exploitation Attempt · Sigma
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Published by SigmaHQ/sigma ↗, licensed under Detection Rule License 1.1 ↗. Reproduced here unmodified. 
title: CVE-2021-41773 Exploitation Attempt
id: 3007fec6-e761-4319-91af-e32e20ac43f5
status: test
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.
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/9d2889356eebba661c8407038e430759dfd4ec31/cves/2021/CVE-2021-41773.yaml
    - https://twitter.com/bl4sty/status/1445462677824761878
author: daffainfo, Florian Roth
date: 2021-10-05
modified: 2023-01-02
tags:
    - attack.initial-access
    - attack.t1190
    - cve.2021-41773
    - detection.emerging-threats
logsource:
    category: webserver
detection:
    selection:
        cs-uri-query|contains:
            - '/cgi-bin/.%2e/'
            - '/icons/.%2e/'
            - '/cgi-bin/.%%32%65/'
            - '/icons/.%%32%65/'
            - '/cgi-bin/.%%%25%33'
            - '/icons/.%%%25%33'
        sc-status:
            - 200
            - 301
    condition: selection
falsepositives:
    - Unknown
level: high

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