A remote code execution vulnerability exists within multiple subsystems of Drupal 7.x and 8.x. This potentially allows attackers to exploit multiple attack vectors on a Drupal site, which could result in the site being completely compromised. 
Drupalgeddon2 “is under active attack, and every Drupal site behind our network is being probed constantly from multiple IP addresses,” Daniel Cid, CTO and founder of security firm Sucuri, told Ars. “Anyone that has not patched is hacked already at this point. Since the first public exploit was released, we are seeing this arms race between the criminals as they all try to hack as many sites as they can.” 
The mass exploitation of Drupal servers harkens back to the epidemic of unpatched Windows servers a decade ago, which gave criminal hackers a toehold in millions of PCs. The attackers would then use their widely distributed perches to launch new intrusions. Because website servers typically have much more bandwidth and computing power than PCs, the new rash of server compromises poses a potentially much greater threat to the Internet. 
Drupal maintainers have patched the critical vulnerability in both the 7.x and 8.x version families as well as the 6.x family, which maintainers stopped supporting in 2016. Administrators who have yet to install the patch should assume their systems are compromised and take immediate action to disinfect them.