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Cyber lab designed for analyzing shellcode, exploring memory exploits and supporting malware analysis

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Introduction

shadow-shell is a cyber lab designed for:

  • analyzing shellcode
  • exploring memory exploits
  • supporting malware analysis

Repository structure

The repository contains two main parts:

  • arsenal: command line tools to support malware analysis
    • shexec: a shellcode runner that can be combined with other tools like strace (Linux), ProcMon and TCPView (Windows) to analyze shellcode functionality
    • stalk-syscalls.js: A Frida syscall tracer script that can be used as an alternative to strace
  • lab: experimental code snippets, some are documented while others are not

⚠️ You should never execute untrusted shellcode on your system. Use an emulator, hardened VM or container for this purpose.

arsenal/
├── linux/
│   ├── arm64/
│   │   ├── shexec.s: Linux ARM64 shellcode runner
│   │   ├── shcode_hello.s: Linux ARM64 shellcode that prints "Hello!"
│   │   ├── shcode_shell.s: Linux ARM64 shellcode that opens a shell
│   │   └── stalk-syscalls.js: Frida ARM64 syscall tracer script
│   ├── x64/
│   │   ├── shexec.s: Linux x64 shellcode runner
│   │   ├── shcode_hello.s: Linux x64 shellcode that prints "Hello, World!"
│   │   └── stalk-syscalls.js: Frida x64 syscall tracer script
│   └── shexec.c: Linux shellcode runner (used as a reference while implementing shexec.s for different architectures)
└── windows/
    └── shexec.c: Windows shellcode runner

lab/
├── linux/
│   ├── buffer-overflow/: proof of concept for a buffer overflow with the goal of executing shellcode
│   └── frida/: experimental Frida scripts
└── windows/
    └── shellcode/: proof of concept for basic shellcode execution

Both POCs are documented in detail on my blog:

Workflow

Shellcode analysis

  1. Emulate the shellcode
    Use an emulator like Qiling to analyze the shellcode.

  2. Fallback to shexec + strace / shexec + Sysinternals
    If you suspect the shellcode may detect the emulator (and behave differently as a result) switch to using shexec with strace (Linux) or shexec + Sysinternals (Windows).

  3. Fallback to frida
    If the shellcode seems to detect tracing by strace or Sysinternals use frida.

  4. Fallback to eBPF tracing (Linux only)
    If the shellcode seems to detect tracing by frida use eBPF tracing. If you do not want to implement the eBPF probes yourself, you can use tools like Stratoshark.

How to build

Prerequisites

$ sudo dnf install docker
$ sudo dnf install mingw64-gcc
$ sudo dnf install nasm
$ sudo dnf install llvm
$ pip install frida-tools
$ rustup target add x86_64-pc-windows-gnu

x64 codebase

$ make x64

ARM64 codebase

I have an x64 PC so to quickly build ARM64 binaries my preference is to use an ARM64v8 Docker container.

$ sudo docker build --platform=linux/arm64 -t arm64 .
$ sudo docker run --platform=linux/arm64 --user $(id -u):$(id -g) --rm -it -v "$(pwd)":/workspace arm64 /bin/bash
$ make arm64

The image is also available on Docker Hub:

$ docker pull gemesa/arm64:latest

Alternatively an ARM64 cross-compiler could also be used.

$ dnf search *aarch64*
$ sudo dnf install gcc-aarch64-linux-gnu
$ sudo dnf install binutils-aarch64-linux-gnu
$ sudo dnf install qemu-system-aarch64
$ sudo dnf install qemu-system-aarch64-core
$ sudo dnf install qemu-user-static-aarch64
$ sudo dnf install sysroot-aarch64-fc41-glibc

Quick guide:

$ aarch64-linux-gnu-gcc -L /usr/aarch64-redhat-linux/sys-root/fc41/lib64 -L /usr/aarch64-redhat-linux/sys-root/fc41/lib --sysroot=/usr/aarch64-redhat-linux/sys-root/fc41 arsenal/linux/arm64/shexec.s -o shexec
$ aarch64-linux-gnu-as arsenal/linux/arm64/shcode_hello.s -o shcode_hello.o
$ aarch64-linux-gnu-ld shcode_hello.o -o shcode_hello
$ llvm-objcopy -O binary --only-section=.text shcode_hello shcode_hello.bin

To build the ARM64 binaries simply use the following command (ensure that the ARM64 cross-compiler is installed):

$ make arm64x

How to run

Linux ARM64

shexec

strace (QEMU)

$ dnf search *aarch64*
$ sudo dnf install qemu-system-aarch64
$ sudo dnf install qemu-system-aarch64-core
$ sudo dnf install qemu-user-static-aarch64

$ qemu-aarch64 -L /usr/aarch64-redhat-linux/sys-root/fc41/usr build/linux/arm64x/shexec build/linux/arm64x/shcode_hello.bin
file size: 52 bytes
Hello!
$ strace qemu-aarch64 -L /usr/aarch64-redhat-linux/sys-root/fc41/usr build/linux/arm64x/shexec build/linux/arm64x/shcode_hello.bin
...
mprotect(0x7f4956b7c000, 4096, PROT_READ) = 0
write(1, "Hello!\n", 7Hello!
)                 = 7
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], NULL, 8) = 0
exit_group(0)                           = ?
+++ exited with 0 +++

gdb (QEMU)

$ qemu-aarch64 -L /usr/aarch64-redhat-linux/sys-root/fc41/usr -g 1234 build/linux/arm64x/shexec build/linux/arm64x/shcode_hello.bin &
$ gdb
gef➤  set architecture aarch64
gef➤  target remote localhost:1234
(remote) gef➤ b _start
(remote) gef➤ c

strace (Docker on arm64 host)

$ sudo docker build --platform=linux/arm64 -t arm64 .
$ sudo docker run --platform=linux/arm64 --user $(id -u):$(id -g) --rm -it -v "$(pwd)":/workspace arm64 /bin/bash
$ strace build/linux/arm64/shexec build/linux/arm64/shcode_hello.bin
...
openat(AT_FDCWD, "build/linux/arm64/shcode_hello.bin", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0755, st_size=52, ...}) = 0
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0), ...}) = 0
getrandom("\x96\x76\xa8\x10\x42\x3b\x3b\x85", 8, GRND_NONBLOCK) = 8
brk(NULL)                               = 0x556f3c0000
brk(0x556f3e1000)                       = 0x556f3e1000
write(1, "file size: 52 bytes\n", 20file size: 52 bytes
)   = 20
mmap(NULL, 52, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f987c6000
read(3, "\1\251\214\322\201\215\255\362\341-\304\362A\1\340\362\341\217\37\370 \0\200\322\341\3\0\221\342\0\200\322"..., 52) = 52
close(3)                                = 0
mprotect(0x7f987c6000, 52, PROT_READ|PROT_WRITE|PROT_EXEC) = 0
write(1, "Hello!\n", 7Hello!
)                 = 7
exit(0)                                 = ?
+++ exited with 0 +++

strace (native)

$ ./build/linux/arm64/shexec build/linux/arm64/shcode_hello.bin
file size: 52 bytes
Hello!
$ echo $$
1918
$ ./build/linux/arm64/shexec build/linux/arm64/shcode_shell.bin
file size: 40 bytes
$ echo $$
19341
$ exit
$ strace ./build/linux/arm64/shexec build/linux/arm64/shcode_hello.bin
...
openat(AT_FDCWD, "build/linux/arm64/shcode_hello.bin", O_RDONLY) = 3
newfstatat(3, "", {st_mode=S_IFREG|0755, st_size=52, ...}, AT_EMPTY_PATH) = 0
newfstatat(1, "", {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0), ...}, AT_EMPTY_PATH) = 0
getrandom("\x20\xc3\xbe\x6a\x9d\x68\x76\xf9", 8, GRND_NONBLOCK) = 8
brk(NULL)                               = 0x55754e8000
brk(0x5575509000)                       = 0x5575509000
write(1, "file size: 52 bytes\n", 20file size: 52 bytes
)   = 20
mmap(NULL, 52, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7facfe6000
read(3, "\1\251\214\322\201\215\255\362\341-\304\362A\1\340\362\341\217\37\370 \0\200\322\341\3\0\221\342\0\200\322"..., 52) = 52
close(3)                                = 0
mprotect(0x7facfe6000, 52, PROT_READ|PROT_WRITE|PROT_EXEC) = 0
write(1, "Hello!\n", 7Hello!
)                 = 7
exit(0)                                 = ?

frida (native)

$ frida -l arsenal/linux/arm64/stalk-syscalls.js -f build/linux/arm64/shexec build/linux/arm64/shcode_hello.bin
     ____
    / _  |   Frida 16.5.9 - A world-class dynamic instrumentation toolkit
   | (_| |
    > _  |   Commands:
   /_/ |_|       help      -> Displays the help system
   . . . .       object?   -> Display information about 'object'
   . . . .       exit/quit -> Exit
   . . . .
   . . . .   More info at https://frida.re/docs/home/
   . . . .
   . . . .   Connected to Local System (id=local)
Spawned `build/linux/arm64/shexec build/linux/arm64/shcode_hello.bin`. Resuming main thread!
file size: 52 bytes
syscall @ 0x7f94453ac8, X8: 0xe2 (226)
[Local::shexec ]-> syscall @ 0x7f9452d024, X8: 0x40 (64) -> write()
    X0: 0x1
    X1: Hello!

    X2: 0x7
Process terminated
[Local::shexec ]->

Thank you for using Frida!

frida (Docker on arm64 host)

$ sudo docker build --platform=linux/arm64 -t arm64 .
$ sudo docker run --platform=linux/arm64 --user $(id -u):$(id -g) --rm -it -v "$(pwd)":/workspace arm64 /bin/bash
$ frida -l arsenal/linux/arm64/stalk-syscalls.js -f build/linux/arm64/shexec build/linux/arm64/shcode_hello.bin
     ____
    / _  |   Frida 16.5.9 - A world-class dynamic instrumentation toolkit
   | (_| |
    > _  |   Commands:
   /_/ |_|       help      -> Displays the help system
   . . . .       object?   -> Display information about 'object'
   . . . .       exit/quit -> Exit
   . . . .
   . . . .   More info at https://frida.re/docs/home/
   . . . .
   . . . .   Connected to Local System (id=local)
Spawned `build/linux/arm64/shexec build/linux/arm64/shcode_hello.bin`. Resuming main thread!
file size: 52 bytes
syscall @ 0x7f9d977b08, X8: 0xe2 (226)
[Local::shexec ]-> syscall @ 0x7f9da4f024, X8: 0x40 (64) -> write()
    X0: 0x1
    X1: Hello!

    X2: 0x7
Process terminated
[Local::shexec ]->

Thank you for using Frida!

Linux x64

shexec

strace (QEMU)

$ qemu-x86_64 build/linux/x64/shexec build/linux/x64/shcode_hello.bin
file size: 57 bytes
Hello, World!
$ strace qemu-x86_64 build/linux/x64/shexec build/linux/x64/shcode_hello.bin
...
mprotect(0x7f6f75e27000, 4096, PROT_READ) = 0
write(1, "Hello, World!\n\0", 15Hello, World!
)       = 15
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], NULL, 8) = 0
exit_group(0)                           = ?
+++ exited with 0 +++

gdb (QEMU)

$ qemu-x86_64 -g 1234 build/linux/x64/shexec build/linux/x64/shcode_hello.bin &
$ gdb
gef➤  target remote localhost:1234
(remote) gef➤ b _start
(remote) gef➤ c

strace (Docker on x64 host)

$ sudo docker build -f Dockerfile-x64 -t x64 .
$ sudo docker run --user $(id -u):$(id -g) --rm -it -v "$(pwd)":/workspace x64 /bin/bash
$ strace build/linux/x64/shexec build/linux/x64/shcode_hello.bin
...
openat(AT_FDCWD, "build/linux/x64/shcode_hello.bin", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0755, st_size=57, ...}) = 0
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0), ...}) = 0
getrandom("\x02\xc8\x9f\xe0\xfd\xfa\x65\x34", 8, GRND_NONBLOCK) = 8
brk(NULL)                               = 0x55d90b4ff000
brk(0x55d90b520000)                     = 0x55d90b520000
write(1, "file size: 57 bytes\n", 20file size: 57 bytes
)   = 20
mmap(NULL, 57, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3a41a40000
read(3, "H\307\300\1\0\0\0H\307\307\1\0\0\0H\2155\25\0\0\0H\307\302\17\0\0\0\17\5H\307"..., 57) = 57
close(3)                                = 0
mprotect(0x7f3a41a40000, 57, PROT_READ|PROT_WRITE|PROT_EXEC) = 0
write(1, "Hello, World!\n\0", 15Hello, World!
)       = 15
exit(0)                                 = ?
+++ exited with 0 +++

strace (native)

$ ./build/linux/x64/shexec build/linux/x64/shcode_hello.bin
file size: 57 bytes
Hello, World!
$ msfvenom -p linux/x64/exec CMD='echo \"Hello, World!\"' -f raw -o shellcode.bin
$ ./build/linux/x64/shexec shellcode.bin
file size: 57 bytes
Hello, World!
$ strace ./build/linux/x64/shexec build/linux/x64/shcode_hello.bin 
...
openat(AT_FDCWD, "build/linux/x64/shcode_hello.bin", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0755, st_size=57, ...}) = 0
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0x1), ...}) = 0
getrandom("\xae\x28\x5d\xfd\xd1\xae\x82\x68", 8, GRND_NONBLOCK) = 8
brk(NULL)                               = 0x55c7bbc4d000
brk(0x55c7bbc6e000)                     = 0x55c7bbc6e000
write(1, "file size: 57 bytes\n", 20file size: 57 bytes
)   = 20
mmap(NULL, 57, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f94405b3000
read(3, "H\307\300\1\0\0\0H\307\307\1\0\0\0H\2155\25\0\0\0H\307\302\17\0\0\0\17\5H\307"..., 57) = 57
close(3)                                = 0
mprotect(0x7f94405b3000, 57, PROT_READ|PROT_WRITE|PROT_EXEC) = 0
write(1, "Hello, World!\n\0", 15Hello, World!
)       = 15
exit(0)                                 = ?

frida (native)

$ frida -l arsenal/linux/x64/stalk-syscalls.js -f build/linux/x64/shexec build/linux/x64/shcode_hello.bin
     ____
    / _  |   Frida 16.5.9 - A world-class dynamic instrumentation toolkit
   | (_| |
    > _  |   Commands:
   /_/ |_|       help      -> Displays the help system
   . . . .       object?   -> Display information about 'object'
   . . . .       exit/quit -> Exit
   . . . .
   . . . .   More info at https://frida.re/docs/home/
   . . . .
   . . . .   Connected to Local System (id=local)
Spawned `build/linux/x64/shexec build/linux/x64/shcode_hello.bin`. Resuming main thread!
file size: 57 bytes
Hello, World!
[Local::shexec ]-> syscall @ 0x7f8cf16e3839, RAX: 0xa (10)
syscall @ 0x7f8cf001b01c, RAX: 0x1 (1) -> write()
    RDI: 0x1
    RSI: Hello, World!

    RDX: 0xf
syscall @ 0x7f8cf001b028, RAX: 0x3c (60)

frida (Docker on x64 host)

$ sudo docker build -f Dockerfile-x64 -t x64 .
$ sudo docker run --user $(id -u):$(id -g) --rm -it -v "$(pwd)":/workspace x64 /bin/bash
$ frida -l arsenal/linux/x64/stalk-syscalls.js -f build/linux/x64/shexec build/linux/x64/shcode_hello.bin
     ____
    / _  |   Frida 16.5.9 - A world-class dynamic instrumentation toolkit
   | (_| |
    > _  |   Commands:
   /_/ |_|       help      -> Displays the help system
   . . . .       object?   -> Display information about 'object'
   . . . .       exit/quit -> Exit
   . . . .
   . . . .   More info at https://frida.re/docs/home/
   . . . .
   . . . .   Connected to Local System (id=local)
Spawned `build/linux/x64/shexec build/linux/x64/shcode_hello.bin`. Resuming main thread!
file size: 57 bytes
Hello, World!
[Local::shexec ]-> syscall @ 0x7f8c4c216c19, RAX: 0xa (10)
syscall @ 0x7f8c4c30401c, RAX: 0x1 (1) -> write()
    RDI: 0x1
    RSI: Hello, World!

    RDX: 0xf
syscall @ 0x7f8c4c304028, RAX: 0x3c (60)

Windows x64

shexec.exe

Native

$ msfconsole
msf6 > info payload/windows/x64/shell_bind_tcp
...
Basic options:
Name      Current Setting  Required  Description
----      ---------------  --------  -----------
EXITFUNC  process          yes       Exit technique (Accepted: '', seh, thread, process, none)
LPORT     4444             yes       The listen port
RHOST                      no        The target address

Description:
  Listen for a connection and spawn a command shell (Windows x64)
...
msf6 > exit
$ msfvenom -p windows/x64/shell_bind_tcp -f raw -o shellcode.bin

Open ProcMon and TCPView then:

> .\shexec.exe shellcode.bin

TCPView

References

About

Cyber lab designed for analyzing shellcode, exploring memory exploits and supporting malware analysis

shadowshell.io/

Topics

rust exploit assembly x64 x86-64 reverse-engineering shellcode amd64 malware-analysis arm64 malware-research frida aarch64 buffer-overflow exploit-development shellcode-development frida-scripts stack-smashing memory-exploits

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