As amusing as it may sound, the recently-patched ‘Dirty Cow’ Linux kernel vulnerability (CVE-2016-5195) highlights a couple of important points:
- vulnerabilities – even known ones – can remain unpatched in critical software for years; and
- a misconfigured server that allows uploaded files to be executed is easily hacked.
At first glance, the Dirty Cow vulnerability may not seem particularly noteworthy. It doesn’t directly allow for arbitrary code execution. But it does allow an attacker who already has the ability to run arbitrary code on a target system to gain full access to that system via privilege escalation.
A Linux server that allows user uploads of any kind is normally configured so that uploaded files cannot be executed. However, it’s very easy to get this wrong, especially for web servers. Still, in most cases, being able to run an uploaded file remotely isn’t enough to provide the kind of access attackers want. Dirty Cow provides that access.
Anyone running a Linux server is strongly advised to install the available kernel updates for Dirty Cow immediately.