April 9, 2021

Four Bytes of Power: exploiting CVE-2021-26708 in the Linux kernel

Author: Alexander Popov, Positive Technologies

CVE-2021-26708 is assigned to five race condition bugs in the virtual socket implementation of the Linux kernel. I discovered and fixed them in January 2021. In this article I describe how to exploit them for local privilege escalation on Fedora 33 Server for x86_64, bypassing SMEP and SMAP. Today I gave a talk at Zer0Con 2021 on this topic (slides).


I like this exploit. The race condition can be leveraged for very limited memory corruption, which I gradually turn into arbitrary read/write of kernel memory, and ultimately full power over the system. That's why I titled this article "Four Bytes of Power."

December 1, 2020

Linux kernel heap quarantine versus use-after-free exploits

It's 2020. Quarantines are everywhere – and here I'm writing about one, too. But this quarantine is of a different kind.

In this article I'll describe the Linux Kernel Heap Quarantine that I developed for mitigating kernel use-after-free exploitation. I will also summarize the discussion about the prototype of this security feature on the Linux Kernel Mailing List (LKML).

March 17, 2020

CVE-2019-18683: Exploiting a Linux kernel vulnerability in the V4L2 subsystem


This article discloses exploitation of CVE-2019-18683, which refers to multiple five-year-old race conditions in the V4L2 subsystem of the Linux kernel. I found and fixed them at the end of 2019. I gave a talk at OffensiveCon 2020 about it (slides).

Here I'm going to describe a PoC exploit for x86_64 that gains local privilege escalation from the kernel thread context (where the userspace is not mapped), bypassing KASLR, SMEP, and SMAP on Ubuntu Server 18.04.