Apache released a security update with the fixes of the Critical Zero-day vulnerability in Apache HTTP Server 2.4.49 that was exploited in Wide. Users recommended updating the new version Fixed in Apache HTTP Server 2.4.50.

The Apache HTTP Server is a free and open-source cross-platform web server software, released under the terms of Apache License 2.0 With 25% Market share.

Researchers uncovered a Path traversal and file disclosure vulnerability in Apache HTTP Server 2.4.49 which is widely exploited.

The vulnerability (CVE-2021-41773) found in a change made to path normalization in Apache HTTP Server 2.4.49 allows an attacker to 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.”Apache said .

Also fixed another vulnerability (CVE-2021-41524) in 2.4.49 While fuzzing the 2.4.49 httpd, a new null pointer dereference was detected during HTTP/2 request processing by attackers with the help of a specially crafted request that allows an external source to DoS the server.

Remote Code Execution Abilities (CVE-2021-41773)

PoC-Exploit has been released for this Path traversal and file disclosure vulnerability, in which researchers also found that the vulnerability is more critical than it was that allowing attackers to perform remote code execution (RCE).

There are 112,755 Apache Server 2.4.49 running hosts found vulnerable, also by taking advantage of this vulnerability, Attackers can abuse Apache servers running version 2.4.49 not only to read arbitrary files but also to execute arbitrary code on the servers.

Security researcher with the name of Hacker Fantastic in Twitter has released a POC-Exploit which can be used for this attack by upload a file via a path traversal exploit, and set execute permissions on the file that gives them an ability to execute an arbitrary code remotely.

He also pointed that “Exploiting CVE-2021-41773 to execute commands is incredibly easy once mod-cgi has been enabled”

Also, he stated that “There is no need to upload a file on Linux/UNIX type environments and mess with file permissions (although that would work too) – you can exploit this with a simple POST request and run full commands + arguments by passing commands as env vars to /bin/sh”

All the server administrators should ensure their Apache HTTP server environments are running patched versions 2.4.50 and above, also use the  Sigma rules to help detect an active exploit for the zero-day.