Here we go again. Researchers have discovered (actually more like rediscovered) a very bad flaw in the commonly-used GNU C Library, also known as glibc.

The flaw has existed, undiscovered, since 2008. It was discovered and reported to the glibc maintainers in July of 2015 (CVE-2015-7547), but nothing was done about it until Google researchers re-discovered the flaw and reported it on a public security blog.

The glibc maintainers reacted to the Google revelations by developing and publishing a patch. It’s not clear why such a serious vulnerability was not fixed sooner.

But that’s not the end of the story. Any computer or device that runs some flavour of Linux, including most of the world’s web servers and many routers, is potentially vulnerable. Individual software applications that are compiled with glibc are also potentially vulnerable.

Although it’s safe to assume that diligent sysadmins will update their Linux computers, tracking down all the affected software will take time. The Linux firmware running on routers and other network devices will be updated much more slowly, if at all. All of this opens up many exploitation possibilities for the foreseeable future.

The good news is that there are several mitigating factors. Many routers don’t use glibc. In some cases, default settings will prevent exploits from working. Android devices are not vulnerable. Still, this problem is likely to get worse before it gets better.

Update 2016Feb20: Dan Kaminsky just posted his analysis of the glibc vulnerability. It’s very technical, but if you’re looking for a deeper dive into this subject, it’s a great place to start. Dan helpfully explains why it’s difficult to predict just how bad things will get.