CVE-2021-42013: 
Apache HTTP Server vulnerability analysis and mitigation

CVE-2021-42013 is a critical path traversal and remote code execution vulnerability discovered in Apache HTTP Server versions 2.4.49 and 2.4.50. The vulnerability was found to be an insufficient fix for the previous CVE-2021-41773 vulnerability. The issue was disclosed on October 7, 2021, and affects only Apache versions 2.4.49 and 2.4.50, not earlier versions (Apache Vulnerabilities, CVE Details).

The vulnerability allows an attacker to use a path traversal attack to map URLs to files outside the directories configured by Alias-like directives. If files outside of these directories are not protected by the usual default configuration 'require all denied', these requests can succeed. When CGI scripts are enabled for these aliased paths, this could allow for remote code execution (JVN).

Successful exploitation of this vulnerability could lead to unauthorized access to files outside the web root directory and potential remote code execution if CGI scripts are enabled. The vulnerability has a CVSS base score of 7.5 HIGH (JVN).

The vulnerability was fixed in Apache HTTP Server version 2.4.51. Users are strongly recommended to upgrade to this version. For those unable to upgrade immediately, ensuring proper 'require all denied' configurations and disabling CGI scripts can help mitigate the risk (Apache Vulnerabilities).

The vulnerability received significant attention from the security community due to being an incomplete fix for CVE-2021-41773. Security researchers actively shared proof-of-concept exploits and analysis of the vulnerability's impact. The Apache HTTP Server Project responded quickly by releasing version 2.4.51 to address the issue (OSS Security).