Linux Kernel Security

Linux kernel heap feng shui in 2022

An article by Michael S and Vitaly Nikolenko describing the kernel changes that affected exploitation techniques for slab-related vulnerabilities over the last few years.

Fuzzing USB with Raw Gadget

Slides and video from a talk by Andrey Konovalov on fuzzing USB drivers.

The talk covers:

🤖 Raw Gadget — a new interface for emulating USB devices
🪶 Fuzzing in a VM via virtual USB controllers
🔌 Reproducing found bugs via Raspberry Pi Zero

kconfig-hardened-check: new feature

kconfig-hardened-check is a tool for checking the security hardening options of the Linux kernel.

Initially, it supported checking compile-time Kconfig options that are relevant for security.

And now this tool can also check the kernel cmdline options, aka boot parameters.

A Kernel Hacker Meets Fuchsia OS

Alexander Popov (me) published an article about hacking the Zircon microkernel of Fuchsia OS.

Experience in Linux kernel security helped to assess Fuchsia OS from the attacker's point of view.

Summary:
🟪 Fuchsia security architecture
🟪 Exploit development experiments for the Zircon microkernel
🟪 PoC attack planting a rootkit into the microkernel

Tetragone: A Lesson in Security Fundamentals

An article by Pawel Wieczorkiewicz and Brad Spengler about bypassing post-exploitation detection provided by Tetragon.

The article also expands on the impossibility of preventing malicious post-exploitation activity if the prevention component works at the same privilege level as the attacked code.

Similar concerns affect LKRG. Check out the LKRG bypass article by Alexander Popov for the details.

Exploiting Dirty Pipe on Android

Two publications about exploiting Dirty Pipe on Android. Both use similar techniques without additional vulnerabilities.

1. Notes and an exploit by polygraphene.

2. Slides by Giovanni Rocca.

Learning Linux kernel exploitation — Part 2 — CVE-2022-0847

A detailed article by 0xricksanchez about the Dirty Pipe vulnerability and its exploitation. The article also recaps Dirty Cow and compares it to Dirty Pipe.

Looking for Remote Code Execution bugs in the Linux kernel

I wrote an article about fuzzing the Linux kernel network stack externally with syzkaller.

The article covers:

🧰 Introduction to syzkaller
💉 Using TUN/TAP for injecting packets into the kernel
🚚 Patching TUN/TAP for collecting coverage via KCOV
👽 Adding pseudo-syscalls for network fuzzing
🗄 Describing packet structure in syzlang
🏆 Showcases of found bugs

In the article, I put a focus on the presentation: highlighted syzlang code, made interactive snippets, added side notes that are actually on the side. I also implemented a dynamic table of contents (only visible on large screens).

The described work was done a few years ago, but I consider it still relevant. The recent trend of looking for remote Linux kernel exploits is quite exciting! I hope to see even more research in this area.

Writing a Linux Kernel Remote [Exploit] in 2022

An article by Samuel Page @sam4k1 about writing an exploit for a remotely-triggerable stack-buffer-overflow in TIPC (CVE-2022-0435).

Assuming the absence of KASLR and the Stack Protector, the exploit overwrites the stack with a ROP chain that hooks a syscall to hijack a root process.

How The Tables Have Turned: An analysis of two new Linux vulnerabilities in nf_tables

A detailed article by David Bouman about exploiting an integer-overflow leading to a limited stack-out-of-bounds read/write in the nf_tables module.

The exploit constructs a filter whose logic depends on the value of a kernel address that happens to be on the stack. This way, it leaks the KASLR offset by observing the side-effects.

The exploit then builds a ROP chain that leaves the softirq context where the bug is triggered, switches to the root network namespace, and gains root privileges.

CVE-2022-27666: Exploit esp6 module in Linux kernel

Xiaochen Zou aka ETenal published an article on exploiting a page_alloc-out-of-bounds in the esp6 crypto module.

The researcher:

1️⃣ performed page-level heap fengshui to gain page_alloc-to-slab overflow,

2️⃣ constructed arbitrary read/write using the msg_msg kernel object,

3️⃣ finally achieved root privileges via modprobe_path overwrite.

The article comes with excellent animated diagrams.

Racing against the clock — hitting a tiny kernel race window

An article by Jann Horn on using hardware timers to widen race condition windows.

Jann applied his method to a race condition in the garbage collector for unix sockets, which had a race window of only 12 instructions.

The article also contains Jann's investigations on the precision of hardware timers in Intel CPUs.

The Discovery and Exploitation of CVE-2022-25636

Nick Gregory published an article about exploiting a heap out-of-bounds write in netfilter. The researcher managed to hijack the kernel control flow.

Compilers: The Old New Security Frontier

Brad Spengler published the slides from his talk at BlueHat IL 2022.

He gave an overview of open problems in operating system security and described how compiler plugins could help.

Exploiting CVE-2021-41073 in io_uring

Valentina Palmiotti published an excellent write-up about exploiting a type confusion in io_uring to gain root privileges.

This bug allows freeing arbitrary slab allocations from the kmalloc-32 cache.

Valentina described how she constructed these exploit primitives:

✔️ UAF in kmalloc-32
✔️ Kernel heap info-leak
✔️ Control flow hijacking
✔️ Illegal privilege escalation

The researcher also described her experience with responsible disclosure.

The Dirty Pipe Vulnerability

An article by Max Kellermann about Dirty Pipe — a logical bug in the memory subsystem that allows writing to read-only files. The provided proof-of-concept works starting from Linux kernel version 5.8 released in August 2020.

The exploit makes the kernel merge a page cache entry belonging to a read-only file with another entry belonging to a pipe and thus writable by the user. This allows overwriting the in-memory contents of the read-only file.

Extending the proof-of-concept provided by Max Kellermann, Blasty has published an exploit for overwriting the contents of a SUID binary and getting root privileges.

Update: Another exploit. This one overwrites /etc/password. By Arinerron.

How to simplify exploiting CVE-2021-26708 using sshd

HardenedVault published a nice write-up that describes how to simplify my PoC exploit for CVE-2021-26708 in the Linux kernel.

They discovered how to perform heap spraying in the cred_jar slab cache for privilege escalation.

CVE-2022-0185: Exploiting a kernel heap buffer overflow for LPE

clubby789 published a detailed write-up about discovering and exploiting CVE-2022-0185 in the FS subsystem of the Linux kernel.

Exploit primitives:
▪️Kernel pointer leak and arbitrary writing using msg_msg
▪️Exploiting FUSE to control the race condition
▪️Overwriting the modprobe_path for privilege escalation

Zenith: Linux kernel RCE exploit for NetUSB driver

Axel Souchet published the Zenith exploit used at Pwn2Own Austin 2021.

Zenith exploits a memory corruption vulnerability in the NetUSB proprietary driver to get remote code execution on the TP-Link Archer C7 V5 router.

This router has no KASLR and executable kernel heap (unbelievable!).

Linux kernel Use-After-Free (CVE-2021-23134) PoC

An article by @Awarau1 about exploiting a use-after-free in NFC sockets to leak /etc/shadow.

Amusingly, uses TeX formatting on web to explain the exploit.