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System for emulation and dynamic analysis of Linux-based firmware

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Table of Contents

Introduction

FIRMADYNE is an automated and scalable system for performing emulation and dynamic analysis of Linux-based embedded firmware. It includes the following components:

  • modified kernels (MIPS: v2.6, ARM: v4.1, v3.10) for instrumentation of firmware execution;
  • a userspace NVRAM library to emulate a hardware NVRAM peripheral;
  • an extractor to extract a filesystem and kernel from downloaded firmware;
  • a small console application to spawn an additional shell for debugging;
  • and a scraper to download firmware from 42+ different vendors.

We have also written the following three basic automated analyses using the FIRMADYNE system.

  • Accessible Webpages: This script iterates through each file within the filesystem of a firmware image that appears to be served by a webserver, and aggregates the results based on whether they appear to required authentication.
  • SNMP Information: This script dumps the contents of the public and private SNMP v2c communities to disk using no credentials.
  • Vulnerability Check: This script tests for the presence of 60 known vulnerabilities using exploits from Metasploit. In addition, it also checks for 14 previously-unknown vulnerabilities that we discovered. For more information, including affected products and CVE's, refer to analyses/README.md.

In our 2016 Network and Distributed System Security Symposium (NDSS) paper, titled Towards Automated Dynamic Analysis for Linux-based Embedded Firmware, we evaluated the FIRMADYNE system over a dataset of 23,035 firmware images, of which we were able to extract 9,486. Using 60 exploits from the Metasploit Framework, and 14 previously-unknown vulnerabilities that we discovered, we showed that 846 out of 1,971 (43%) firmware images were vulnerable to at least one exploit, which we estimate to affect 89+ different products. For more details, refer to our paper linked above.

Note: This project is a research tool, and is currently not production ready. In particular, some components are quite immature and rough. We suggest running the system within a virtual machine. No support is offered, but pull requests are greatly appreciated, whether for documentation, tests, or code!

Setup

First, clone this repository recursively and install its dependencies.

  1. sudo apt-get install busybox-static fakeroot git dmsetup kpartx netcat-openbsd nmap python-psycopg2 python3-psycopg2 snmp uml-utilities util-linux vlan
  2. git clone --recursive https://github.com/firmadyne/firmadyne.git

Extractor

The extractor depends on the binwalk tool, so we need to install that and its dependencies.

  1. git clone https://github.com/ReFirmLabs/binwalk.git
  2. cd binwalk
  3. sudo ./deps.sh
  4. sudo python ./setup.py install
  • For Python 2.x, sudo apt-get install python-lzma
  1. sudo -H pip install git+https://github.com/ahupp/python-magic
  2. sudo -H pip install git+https://github.com/sviehb/jefferson.
  3. Optionally, instead of upstream sasquatch, our sasquatch fork can be used to prevent false positives by making errors fatal.

Database

Next, install, set up, and configure the database.

  1. sudo apt-get install postgresql
  2. sudo -u postgres createuser -P firmadyne, with password firmadyne
  3. sudo -u postgres createdb -O firmadyne firmware
  4. sudo -u postgres psql -d firmware < ./firmadyne/database/schema

Binaries

To download our pre-built binaries for all components, run the following script:

  • cd ./firmadyne; ./download.sh

Alternatively, refer to the instructions below to compile from source.

QEMU

To use QEMU provided by your distribution:

  • sudo apt-get install qemu-system-arm qemu-system-mips qemu-system-x86 qemu-utils

Note that emulation of x86-based firmware is not currently supported, but installing qemu-system-x86 resolves a packaging issue on certain Debian-based distributions.

Alternatively, use our modified version of qemu-linaro for certain firmware with an alphafs webserver that assumes a fixed memory mapping (not recommended), or upstream qemu.

Usage

  1. Set FIRMWARE_DIR in firmadyne.config to point to the root of this repository.
  2. Download a firmware image, e.g. v2.0.3 for Netgear WNAP320.
    • wget http://www.downloads.netgear.com/files/GDC/WNAP320/WNAP320%20Firmware%20Version%202.0.3.zip
  3. Use the extractor to recover only the filesystem, no kernel (-nk), no parallel operation (-np), populating the image table in the SQL server at 127.0.0.1 (-sql) with the Netgear brand (-b), and storing the tarball in images.
    • ./sources/extractor/extractor.py -b Netgear -sql 127.0.0.1 -np -nk "WNAP320 Firmware Version 2.0.3.zip" images
  4. Identify the architecture of firmware 1 and store the result in the image table of the database.
    • ./scripts/getArch.sh ./images/1.tar.gz
  5. Load the contents of the filesystem for firmware 1 into the database, populating the object and object_to_image tables.
    • ./scripts/tar2db.py -i 1 -f ./images/1.tar.gz
  6. Create the QEMU disk image for firmware 1.
    • sudo ./scripts/makeImage.sh 1
  7. Infer the network configuration for firmware 1. Kernel messages are logged to ./scratch/1/qemu.initial.serial.log.
    • ./scripts/inferNetwork.sh 1
  8. Emulate firmware 1 with the inferred network configuration. This will modify the configuration of the host system by creating a TAP device and adding a route.
    • ./scratch/1/run.sh
  9. The system should be available over the network, and is ready for analysis. Kernel messages are mirrored to ./scratch/1/qemu.final.serial.log. The filesystem for firmware 1 can be mounted to and unmounted from scratch/1/image with ./scripts/mount.sh 1 and ./scripts/umount.sh 1.
    • ./analyses/snmpwalk.sh 192.168.0.100
    • ./analyses/webAccess.py 1 192.168.0.100 log.txt
    • mkdir exploits; ./analyses/runExploits.py -t 192.168.0.100 -o exploits/exploit -e x (requires Metasploit Framework)
    • sudo nmap -O -sV 192.168.0.100
  10. The default console should be automatically connected to the terminal. You may also login with root and password. Note that Ctrl-c is sent to the guest; use the QEMU monitor command Ctrl-a + x to terminate emulation.

FAQ

run.sh is not generated

This is a common error that is encountered when the network configuration is unable to be inferred. Follow the checklist below to figure out the cause.

  1. inferNetwork.sh: Did this script find any network interfaces (e.g. Interfaces: [br0, 192.168.0.1])? If so, this is a bug; please report it. Otherwise, continue below.
  2. qemu.initial.serial.log: Does this file end with Unable to mount root fs on unknown-block(8,1)? If so, the initial filesystem image was not generated correctly using kpartx. Try deleting the scratch directory corresponding to this firmware image, and restart at makeImage.sh. Otherwise, the initial emulation didn't produce any useful instrumentation. Try increasing the timeout in inferNetwork.sh from 60 to 120 and restarting at inferNetwork.sh.
  3. qemu.initial.serial.log: Did the init process crash, and is this preceded by a failed NVRAM operation (e.g. nvram_get_buf: Unable to open key <foo>)? If so, see the FAQ entries below.

Log ends with "Kernel panic - not syncing: No working init found"

The firmware uses an initialization process with an unusual name. You'll need to manually inspect the filesystem to identify the correct one, then modify the script to specify its full path by appending a kernel boot parameter init=<path> to QEMU.

A process crashed, e.g. do_page_fault() #2: sending SIGSEGV for invalid read access from 00000000

It is likely that the process requested a NVRAM entry that FIRMADYNE does not have a default value for. This can be fixed by manually adding a source for NVRAM entries to NVRAM_DEFAULTS_PATH, an entry to NVRAM_DEFAULTS, or a file to OVERRIDE_POINT in libnvram. For more details, see the documentation for libnvram. Note that the first two options involve modifying config.h, which will require recompilation of libnvram.

How do I debug the emulated firmware?

  1. With full-system QEMU emulation, compile a statically-linked gdbserver for the target architecture, copy it into the filesystem, attach it to the process of interest, and connect remotely using gdb-multiarch. You'll need a cross-compile toolchain; either use the crossbuild-essential-* packages supplied by Debian/Ubuntu, build it from scratch using e.g. buildroot, or look for GPL sources and/or pre-compiled binaries online. If you have IDA Pro, you can use IDA's pre-compiled debug servers (located in the dbgsrv subdirectory of the install), though they are not GDB-compatible.
  2. With full-system QEMU emulation, pass the -s -S parameters to QEMU and connect to the stub using target remote localhost:1234 from gdb-multiarch. However, the debugger won't automatically know where kernel and userspace is in memory, so you may need to manually do add-symbol-file in gdb and break around try_to_run_init_process() in the kernel.
  3. With user-mode QEMU emulation, chroot into the firmware image (optional), set LD_LIBRARY_PATH to contain the FIRMADYNE libnvram, and pass both the -L parameter with the correct path to the firmware /lib directory, and the binary of interest to QEMU. This is easiest to debug, because you can attach directly to the process using gdb-multiarch, and interact directly with the process, but the system state may not be accurate since the host kernel is being used. It is also somewhat insecure, because the emulated firmware can access the host filesystem and interact with the host kernel.

Compiling from Source

If you would like to compile the entire FIRMADYNE system from scratch without using our pre-built binaries, please follow the steps below.

Toolchain

In order to build any of the binaries used by FIRMADYNE, you will need three cross-compilation toolchains for the following architecture triples. Use only musl libc as the C runtime library for the toolchain; others have not been tested.

  • arm-linux-musleabi
  • mipseb-linux-musl
  • mipsel-linux-musl

To simplify the process of building cross-compilation toolchains with musl, we recommend using the musl-cross project. Follow the below steps to build these toolchains from source, or alternatively click here to download our pre-built toolchains.

  1. git clone https://github.com/GregorR/musl-cross.git

  2. Modify or set the following variables in defs.sh

    • BINUTILS_URL=http://ftp.gnu.org/gnu/binutils/binutils-2.25.1.tar.bz2
    • GCC_VERSION=5.3.0
    • GMP_VERSION=6.0.0a
    • MPC_VERSION=1.0.2
    • MPFR_VERSION=3.1.3
    • LIBELF_VERSION=master
    • MUSL_DEFAULT_VERSION=1.1.12
    • MUSL_GIT_VERSION=615629bd6fcd6ddb69ad762e679f088c7bd878e2
    • LANG_CXX=no
    • GCC_BUILTIN_PREREQS=yes

  3. Modify or set the following variables in config.sh

    • CFLAGS="-fPIC"

  4. For little-endian MIPS, perform the following:

    • set TRIPLE=mipsel-linux-musl in config.sh
    • set LINUX_HEADERS_URL=https://mirrors.edge.kernel.org/pub/linux/kernel/v2.6/linux-2.6.39.4.tar.xz in defs.sh
    • run ./clean.sh to clean out any previous builds
    • run ./build.sh to build and install the toolchain into /opt/cross

  5. For big-endian MIPS, perform the following:

    • set TRIPLE=mipseb-linux-musl in config.sh
    • set LINUX_HEADERS_URL=https://mirrors.edge.kernel.org/pub/linux/kernel/v2.6/linux-2.6.39.4.tar.xz in defs.sh
    • run ./clean.sh to clean out any previous builds
    • run ./build.sh to build and install the toolchain into /opt/cross

  6. For little-endian ARM, perform the following:

    • set TRIPLE=arm-linux-musleabi, GCC_BOOTSTRAP_CONFFLAGS="--with-arch=armv6 --with-float=softfp", and GCC_CONFFLAGS="--with-arch=armv6 --with-float=softfp" in config.sh
    • set LINUX_HEADERS_URL=https://kernel.org/pub/linux/kernel/v4.x/linux-4.1.17.tar.xz in defs.sh
    • run ./clean.sh to clean out any previous builds
    • run ./build.sh to build and install the toolchain into /opt/cross

  7. You should have the following directories, or wherever you installed the toolchains:

    • /opt/cross/arm-linux-musleabi
    • /opt/cross/mipseb-linux-musl
    • /opt/cross/mipsel-linux-musl

console

  1. cd ./firmadyne/sources/console
  2. make clean && CC=/opt/cross/arm-linux-musleabi/bin/arm-linux-musleabi-gcc make && mv console ../../binaries/console.armel
  3. make clean && CC=/opt/cross/mipseb-linux-musl/bin/mipseb-linux-musl-gcc make && mv console ../../binaries/console.mipseb
  4. make clean && CC=/opt/cross/mipsel-linux-musl/bin/mipsel-linux-musl-gcc make && mv console ../../binaries/console.mipsel

libnvram

  1. cd ./firmadyne/sources/libnvram
  2. make clean && CC=/opt/cross/arm-linux-musleabi/bin/arm-linux-musleabi-gcc make && mv libnvram.so ../../binaries/libnvram.so.armel
  3. make clean && CC=/opt/cross/mipseb-linux-musl/bin/mipseb-linux-musl-gcc make && mv libnvram.so ../../binaries/libnvram.so.mipseb
  4. make clean && CC=/opt/cross/mipsel-linux-musl/bin/mipsel-linux-musl-gcc make && mv libnvram.so ../../binaries/libnvram.so.mipsel

Kernel

ARM

  1. git clone https://github.com/firmadyne/kernel-v4.1.git && cd kernel-v4.1
  2. mkdir -p build/armel
  3. cp config.armel build/armel/.config
  4. make ARCH=arm CROSS_COMPILE=/opt/cross/arm-linux-musleabi/bin/arm-linux-musleabi- O=./build/armel zImage -j8
  5. cp build/armel/arch/arm/boot/zImage ../firmadyne/binaries/zImage.armel

MIPS

  1. git clone https://github.com/firmadyne/kernel-v2.6.git && cd kernel-v2.6

  2. For big-endian MIPS, perform the following:

    1. mkdir -p build/mipseb
    2. cp config.mipseb build/mipseb/.config
    3. make ARCH=mips CROSS_COMPILE=/opt/cross/mipseb-linux-musl/bin/mipseb-linux-musl- O=./build/mipseb -j8
    4. cp build/mipseb/vmlinux ../firmadyne/binaries/vmlinux.mipseb

  3. For little-endian MIPS, perform the following:

    1. mkdir -p build/mipsel
    2. cp config.mipsel build/mipsel/.config
    3. make ARCH=mips CROSS_COMPILE=/opt/cross/mipsel-linux-musl/bin/mipsel-linux-musl- O=./build/mipsel -j8
    4. cp build/mipsel/vmlinux ../firmadyne/binaries/vmlinux.mipsel

Database

During development, the database was stored on a PostgreSQL server.

Data

Although we cannot redistribute binary firmware, the data used for our experiments is available here.

Schema

Below are descriptions of tables in the schema.

  • brand: Stores brand names for each vendor.
Column Description
id Primary key
name Brand name
  • image: Stores information about each firmware image.
Column Description
id Primary key
filename File name
brand_id Foreign key to brand
hash MD5
rootfs_extracted Whether the primary filesystem was extracted
kernel_extracted Whether the kernel was extracted
arch Hardware architecture
kernel_version Version of the extracted kernel
  • object: Stores information about each file in a filesystem.
Column Description
id Primary key
hash MD5
  • object_to_image: Maps unique files to their firmware images.
Column Description
id Primary key
oid Foreign key to object
iid Foreign key to image
filename Full path to the file
regular_file Whether the file is regular
permissions File permissions in octal
uid Owner's user ID
gid Group's group ID
  • product
Column Description
id Primary key
iid Foreign key to image
url Download URL
mib_filename Filename of the SNMP MIB
mib_hash MD5 of the SNP MIB
mib_url Download URL of the SNMP MIB
sdk_filename Filename of the source SDK
sdk_hash MD5 of the source SDK
sdk_url Download URL of the source SDK
product Product name
version Version string
build Build string
date Release date

Paper

The results discussed in our paper were produced using pre-release versions of the following:

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System for emulation and dynamic analysis of Linux-based firmware

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