cerodah/overlayfs-cve-2021-34932021 kernel vulnerability in Ubuntu.
OverlayFS is a Linux kernel module that allows the system to combine multiple mount points into one, so that it can access all files from each within a single directory structure.
Recently SSD-Discloure released a PoC for an exploit of the Ubuntu kernel (link). This vulnerability was very serious because OverlayFS was installed by default on Ubuntu1804 Server. If such a system is vulnerable, it is easy to escalate to root user. But only if you can execute a binary
As we can see, the SSH server has a C compiler installed. We use it to compile it and then execute it. And we would be root.
