This error, called CVE-2019-0211, is a local privilege escalation bug, which means that it allows a person or software that already has limited access to a server to acquire root privileges. From there, the attacker could do almost everything in one system. According to Charles Fol, a researcher who discovered the error, vulnerability makes it possible for unauthorized intruders to replace sensitive parts of a server's memory. A malicious script could exploit the vulnerability to gain root access.
Vulnerability poses the greatest risk to Web-hosting installations that offer common impressions where a machine provides content for more than one site. Typically, these servers prevent a site administrator from accessing other sites or accessing sensitive settings of the machine itself.
"If one of the users successfully exploits the vulnerability, it will have full access to the server, just like the web hoster," said Fol. "This means reading / writing / deleting any other user's file / database."
The other possible script for exploitation is the case that an attacker using a different attack gains only limited privileges on a server running Apache. If the server is vulnerable to CVE-2019-0211, the attacker could take advantage of the flaw to increase these limited permissions to root.
Vulnerability affects only versions of Apache 2.4.17 to 2.4.38 when running on UNIX-like systems. According to the Rapid7 security company, about 2 million different systems were vulnerable to CVE-2019-0211, though most likely were updated since the bug was published.