Linux
The open-source operating system behind most servers.
Where It Sits
The small stack marks its layer. Beside it, each related technology links to its own page.
- App
- Framework
- Web Server
- Runtime
- Containers
- OSLinux
- Hypervisor
- Firmware
- Hardware
- Data
About
Linux is the operating system behind most web servers and cloud instances. It runs the web server, the runtime and the application, and controls the machine's files, users and network. It is a rival to Windows Server on this layer.
How to Spot It
These are signs that a system runs Linux, seen from outside without signing in, such as a response header, a cookie, a path or a default port. They help you find where it runs across your own estate. A version shown to the world also tells anyone scanning which flaws might apply, so it is worth hiding.
- Default port
22 (SSH)- Service banner
SSH-2.0-OpenSSH_9.6p1 Ubuntu-3ubuntu13
If It Has a Flaw
A flaw in the kernel or a privileged service reaches every application on the machine, since the operating system controls them all.
A flaw exposes what runs on it.
- Containers
Docker
Kubernetes
Well-Known Flaws
Each flaw has a CVE id, the unique number a publicly known vulnerability is given so that every advisory names the same flaw. The id links to the advisory, and the card says what the flaw let an attacker do and how far it reached because of where Linux sits.
CVE-2016-5195 (opens in a new tab)2016
Dirty COW
A race condition in the Linux kernel let a local user gain root.
Reach As a kernel flaw, it handed over the whole machine.
Rivals
Rivals do the same job on the same layer, so a system usually runs one of them in any one place. A flaw in a rival does not reach Linux.
Stacks and Code
Linux is part of the common stacks below, and each stack's page shows who runs every layer. Its code arrives from the sources listed, and each source's page says how bad code could get in through it.