Gird your loins internet: Attackers now have the ability to disrupt large swathes of the web through a remote denial of service vulnerability found in the most widely used software for DNS servers.

The BIND bug (CVE-2015-5477) patched overnight affects all DNS servers running the software, and can be attacked with ease.

In fact a researcher has already developed an attack capable of knocking servers offline with a single packet.

Internet Systems Consortium Michael McNally, lead investigator for the bug, says there are no workarounds other than to apply a patch. He expects attacks to happen soon.

"The practical effect of this is that this bug is difficult to defend against (except by patching, which is completely effective) and will not be particularly difficult to reverse-engineer," McNally says.

"I have already been told by one expert that they have successfully reverse-engineered an attack kit from what has been divulged and from analysing the code changes, and while I have complete confidence that the individual who told me this is not intending to use his kit in a malicious manner, there are others who will do so who may not be far behind."

Attackers can send a crafted DNS query packet to trigger a REQUIRE assertion failure, causing BIND to exit.

The bug is labeled a critical fix and "deserves that designation," McNally says.

It stands out among other BIND bugs in that it affects almost all known BIND servers and cannot be mitigated without a patch. Firewalls will likely not help.

Threat Intelligence founder Ty Miller says an en-masse attack is easy and could knock out websites, email, and other online functions.

"From a global scale the Denial of Service could have major implications if it is extended out to thousands of organisations; it could take down websites, email, and disrupt the ability for people to surf the internet," Miller says.

"For organisations it means employees won't be able to get to the internet, or access email and so on."

He says it is a trivial bug to exploit and agrees the impacts of the bug will be soon felt.

While Amazon and RedHat have applied the fixes, Miller says many other DNS operators may not apply the patch since BIND runs on Unix platforms that are not typically patched as often as other systems.

"This kind of stuff tends to stick around for a long time," he says.

Patching could also cause interruptions to businesses if things go wrong.

All DNS operators are told to upgrade to BIND 9 version 9.9.7-P2 or BIND 9 version 9.10.2-P3. ®