Difference between revisions of "Reverse-Engineering"

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More tools at http://wiki.secmobi.com/tools:android_dynamic_analysis
  
More tools at http://wiki.secmobi.com/tools:android_dynamic_analysis
 
* [http://www4.comp.polyu.edu.hk/~csxluo/NDroid.pdf On Tracking Information Flows through JNI in Android Applications (pdf)], A dynamic information flow tracing system for Android, sources [https://github.com/0-14N/NDroid here]
  
* [http://www4.comp.polyu.edu.hk/~csxluo/NDroid.pdf On Tracking Information Flows through JNI in Android Applications (pdf)], A dynamic information flow tracing system for Android, sources [https://github.com/0-14N/NDroid here]
  +
* [https://github.com/BaiduSecurityLabs/ZjDroid ZjDroid] Android app dynamic reverse tool based on Xposed framework (you'd better understand Chinese...)
   
 
==Java==
  
==Java==

Revision as of 21:52, 27 July 2014

Books

Resources

Static Analysis Tools

IDA Pro

Metasm

Metasm is a cross-architecture assembler, disassembler, compiler, linker and debugger.
It has some advanced features such as live process manipulation, GCC/Microsoft Visual Studio-compatible preprocessor, automatic backtracking in the disassembler (similar to "slicing"), C headers shrinking, linux/windows/remote debugging API interface, a C compiler/decompiler, a gdb-server compatible debugger, and various advanced features. It is written in pure Ruby, with no dependency.
Intel IA32 (16/32/64bits), MIPS, PPC. Ongoing: ARM
MZ, PE/COFF (32 and 64 bits), ELF (32 and 64 bits), Mach-O (incomplete) and UniversalBinary

REC Studio

  • x86, x64
  • Windows, Linux, Mac OS X
  • HLA disassembler

Useful commands: 

help
strings
calltree
showprocs
decompile /tmp/myprog.c

click on a function in the "Project" function list to HLA disass it

Hopper

  • Intel (32 and 64bits), and ARM (ARMv6, ARMv7 and ARM64) processors
  • Mach-O binaries (Mac and iOS), PE32/32+/64 Windows binaries and ELF binaries
  • decompiler
  • debugger
  • patcher

Capstone

  • ARM, ARM64 (ARMv8), Mips, PowerPC, Sparc, SystemZ & Intel

Radare

The reverse engineering framework

Bokken

GUI
git repo synced with mercurial repo

Amoco

Amoco is a python package dedicated to the (static) analysis of binaries
Very young but promising, seems easy to add an arch
With BBL symbolic execution

Miasm

Miasm is a a free and open source (GPLv2) reverse engineering framework. Miasm aims at analyzing/modifying/generating binary programs. * opening/modifying/generating PE/ELF 32/64 le/be using Elfesteem

  • Assembling/Disassembling ia32/ppc/arm
  • Representing assembly semantic using intermediate language
  • Emulating using jit (dynamic code analysis, unpacking, ...)
  • Expression simplification for automatic de-obfuscation
  • ...

Medusa

Medusa is a disassembler designed to be both modular and interactive. It runs on Windows and Linux

SmartDec

Native code to C/C++ decompiler
x86 and x86-64 architectures, ELF and PE file formats
IDA Pro & standalone versions, for Windows
Standalone i86 Windows version runs fine under Wine
Beta

Misc

Distorm

diStorm3 is really a decomposer, which means it takes an instruction and returns a binary structure which describes it rather than static text, this is great for advanced binary code analysis

PyPEELF

PyPEELF is a multi-platform binary editor written in Python, wxPython and BOA Constructor. It allows you to manage binary data in PE32, PE32+ (x64) and ELF binary files.

PyPEELF uses pefile to manage PE32 and PE32+ files and pyelf to manage ELF files. Besides, it uses winappdbg and pydasm in some others features like Task Running Viewer and Disassembling files.

PyPEELF was designed for Reverse Engineers who want to edit or visualize binary file data in multi-platforms. That is why PyPEELF runs under Windows and Unix/BSD operating systems

Retargetable decompiler

Support ELF & PE for Intel x86, ARM, ARM+Thumb, MIPS, PIC32, and PowerPC architectures
Online decompilation service available!

binwalk

Binwalk is a fast, easy to use tool for analyzing and extracting firmware images.

PREF

Portable Reverse Engineering Framework
On github 

apt-get install qtbase5-dev ...
qmake
make

Poor man's tools

File, -z to uncompress, -s to inspect non-files, e.g. /dev/sda1 

file -k [-z] [-s] mybin

Strings 

strings [-n min_length] -a -e [s|S|b|l|B|L] mybin

Android

Documentation

  • Dalvik: bytecode, dex & VM instructions

Dex2jar

A tool for converting Android’s .dex format to Java’s .class format
See also DeObfuscate jar with dex tool 

./d2j-dex2jar.sh myapp.apk

This returns a file myapp-dex2jar.jar
Then use Java decompilers: jad, jd-gui, cf below

Smali

smali/baksmali is an assembler/disassembler for the dex format used by dalvik, Android’s Java VM implementation

Apktool

It is a tool for reverse engineering 3rd party, closed, binary Android apps. It can decode resources to nearly original form and rebuild them after making some modifications; it makes possible to debug smali code step by step. Also it makes working with app easier because of project-like files structure and automation of some repetitive tasks like building apk, etc. 

apktool d myapp.apk

Apk Multi-Tool

Swiss knive (was Apk Manager)
Contains apktool, smali/baksmali etc
on Github for Linux release

  • 9 decompile apk / 1 select apk / 9 decompile apk

GetStrings

Small script to prepare a sed script to inject resource strings into jad, to ease reversing.
Update: inject resource names for other resources than strings, will still be more explanatory than 0x7f123456
To be used e.g. after apktool / Apk Multi-Tool decompilation 

#!/bin/bash
DECOMPILED_DIR=working/*apk/
cat $DECOMPILED_DIR/res/values/public.xml|grep "type=.string"|\
    sed 's/.*name="\?//;s/" id="\?/ /;s/"\? \/>//'|\
    awk --non-decimal-data '{print $2, int($2), $1}'\
    > getstring-pub
cat $DECOMPILED_DIR/res/values/strings.xml|grep '<string'|\
    sed 's/.*name="\?//; s/"\?>/ /;s/<\/string>//;s/#/\\#/g'\
    > getstring-str
join -1 3 -2 1 --nocheck-order getstring-pub getstring-str|\
    sed 's/[^ ]\+ \([[:alnum:]]\+\) [[:alnum:]]\+ \(.*\)/s#\1#"\2"#/'\
    > getstring-sed
rm getstring-pub getstring-str
cat $DECOMPILED_DIR/res/values/public.xml|grep "type="|\
    grep -v "type=.string"|\
    sed 's/.*type="\(.*\)" name="\(.*\)" id="\(.*\)" \/>/s#\3#\1:\2#/'\
    >> getstring-sed

SetStrings

find $1 -name "*.jad" -exec sed -i -f getstring-sed {} \;

Soot

Soot is a Java bytecode analysis and transformation framework, now supporting Dalvik too.
Get soot.jar

Help: 

java -jar soot.jar --help|less

SootDisassembleApkToJimple.sh 

#In case you don't have the right platform android.jar, you can force using another one, e.g.:
#FORCEJAR="-force-android-jar /path/to/android-sdk-linux_x86/platforms/android-17/android.jar"
java -jar soot.jar -allow-phantom-refs -android-jars /path/to/android-sdk-linux_x86/platforms -src-prec apk -process-dir $1 -output-format jimple $FORCEJAR

SootAssembleJimpleToDex.sh 

java -jar soot.jar -allow-phantom-refs -android-jars /path/to/android-sdk-linux_x86/platforms -src-prec jimple -process-dir sootOutput -output-format dex
mv sootOutput/classes.dex .

Example

Example of reverse-engineering and modding APK with smali:

  • in APK-Multi-Tool-Linux working dir:
    • Drop myapp.apk in place-apk-here-for-modding/
    • ./script.sh (and leave it always open in a separate window)
    • 9 decompile / 1 select myapp.apk / 9 decompile
    • ./getstrings
    • Copy apk to dex2jar working dir
    • Copy getstring-sed to jad working dir
  • in dex2jar working dir:
    • ./d2j-dex2jar.sh myapp.apk
    • Copy myapp-dex2jar.jar to jad working dir (and/or jd-gui)
  • in jad working dir:
    • ./unjar myapp-dex2jar.jar
    • ./setstrings.sh myapp-dex2jar
    • Analyse .jad file and understand what to modify
  • in jd-gui working dir:
    • As alternative analysis can also be done with jd-gui directly on .jar file
  • in APK-Multi-Tool-Linux working dir:
    • In working/ find corresponding .smali file and modify it
    • (in script.sh windows) 13 compile/sign/install

Example 2

Example of reverse-engineering and modding APK with Soot / jimple

  • in APK-Multi-Tool-Linux working dir:
    • Drop myapp.apk in place-apk-here-for-modding/
    • ./script.sh (and leave it always open in a separate window)
    • 1 extract apk
    • Copy apk to soot working dir
  • in soot working dir:
    • ./SootDisassembleApkToJimple.sh myapp.apk
    • Analyse and modify sootoutput/*.jimple files
    • ./SootAssembleJimpleToDex.sh
    • Copy classes.dex to overwrite APK-Multi-Tool-Linux/out/classes.dex
  • in APK-Multi-Tool-Linux working dir (in script.sh windows)
    • 3 zip apk / 2 regular app
    • 4 sign app
    • adb install place-apk-here-for-modding/repackaged-signed.apk

Dare

Dalvik Retargeting, a tool for converting Android’s .dex format to Java’s .class format

Retargeted .class: 

./dare -d output_dir -e myapp.apk

Optimized retargeted .class: (using Soot, slow!) 

./dare -o -d output_dir -e myapp.apk

Decompiled optimized retargeted .class: (using Soot, very slow!) 

./dare -c -d output_dir -e myapp.apk

APKInspector

The goal of this project is to help analysts and reverse engineers to visualize compiled Android packages and their corresponding DEX code. APKInspector provides both analysis functions and graphic features for the users to gain deep insight into the malicious apps
Still beta and inactive for a year.
GUI around other tools

Androguard

Reverse engineering, Malware analysis of Android applications … and more !

Seems to be able to tackle also dynamically loaded code, native code, reflection code

Dexdump

Java .dex file format decompiler
Inactive since 2009

FlowDroid

FlowDroid is a context-, flow-, field-, object-sensitive and lifecycle-aware static taint analysis tool for Android applications

Mobile Sandbox

Provides online static analysis of malware images.

JEB Decompiler

Commercial ($1000)
Decompile Android apps and obfuscated Dalvik bytecode

Misc

More tools at http://wiki.secmobi.com/tools:android_reversing_analysis

Online decompilation at http://www.decompileandroid.com/ (using dex2jar, jad, apktool, zip/unzip)

Java

JAD

Java Decompiler
To use on a jar (from dex2jar): 

#!/bin/bash
JAD=$(pwd)/jad
ODIR=${1%.jar}
if [ "$ODIR" == "$1" ]; then
    echo "Error: expecting a file ending with .jar"
    exit 1
fi
7z x -o${ODIR} $1
for d in $(find ${ODIR}/com -type d); do
  echo Entering $d
  cd $d
  # Clean Android stuffs
  rm *\$*.class
  for c in *.class; do
    $JAD $c
    # Want to keep the .class or not?
    rm $c
  done
  cd -
done

./unjar myapp-dex2jar.jar

jadretro

Helps converting Java 1.4, Java 1.5 or later classes so JAD gives better results

JadAlign

Aligns java-files, which are decompiled by jad 

java -jar JadHelper-0.0.1.jar myfile.java

No much effect on jad from dex

Jd-gui

JD-GUI is a standalone graphical utility that displays Java source codes of “.class” files

binary-refactor

Helper to manual de-obfuscate obfuscated jars

  • rename class/packages in a jar
  • match a jarjar-ed & obfuscated jar with a known jar,to find the 'same' classes
  • bytecode dump(asm)
  • class dependency graph

dirtyJOE

Java Overall Editor is a complex editor and viewer for compiled java binaries (.class files)

PJB

ELF

man elf

readelf

readelf -a -g -t --dyn-syms -W mybin

elfedit

objdump

objdump -C -g -F -x -T --special-syms mybin
objdump -d -l -r -R -S mybin
objdump -D -l -r -R -S mybin

nm

nm -a -C -S -s --special-syms mybin

ldd

Shared library dependencies: 

ldd -v mybin

PE

Pefile

A Python module to read and work with PE (Portable Executable) files, see usage examples 

#!/usr/bin/env python
import sys, pefile
pe = pefile.PE(sys.argv[1])
pe.dump_info()
open('out.txt', 'w').write(pe.dump_info())

Can run under Linux

PEiD

Can run with Wine

PETools

Can run with Wine

Resource Hacker

Can run with Wine

Dependency Walker

Can run with Wine

PEview

Can run with Wine

DLL Export Viewer

Can run with Wine
Under Wine, require absolute path to DLL so: click on gears, "load functions from the following DLL file", Browse

PEBrowse Pro

Can run with Wine

Explorer Suite

  • CFF Explorer: Allows also to modify a PE
  • Signature Explorer
  • PE Detective
  • Task Explorer (32 & 64)

PE Insider

Static protections

Packers

upx -d myfile
  • http://www.woodmann.com/crackz/Packers.htm
  • Crinkler: some insane PE packing tool coming from the demoscene world.
  • midgetpack Midgetpack is a binary packer for ELF binaries. The curve25519 is the real advantage of midgetpack. In this mode, you do not provide any password or key. Instead, a key file is generated at packing time. This key file must be used every time you wish to use the binary. When you start the binary, it will give a challenge and expect a response.

Dynamic Analysis Tools

IDA Pro

IDA Pro has some debugging capabilities too.
Local debugging: win32, windbg Remote debugging: 

gdbserver --multi <client_ip>:<port> # default IDA port: 23946

Then on IDA: select Remote GDB debugger, paths should be paths on the gdbserver host.
Tuning:

  • Debugger / options / Stop on process entry point
  • Compatible with lib preloading, cf below
  • from 6.4, can make use of Intel PIN tools for diff debugging, see tutorial (pdf)

Metasm

Metasm has debugging capabilities too.

Intel PIN tools

  • Official page
  • Windows, Linux, Mac OS X, Android
  • x86-32, x86-64 (only Intel platforms obviously)
  • binary instrumentation

The best way to think about Pin is as a "just in time" (JIT) compiler. The input to this compiler is not bytecode, however, but a regular executable. Pin intercepts the execution of the first instruction of the executable and generates ("compiles") new code for the straight line code sequence starting at this instruction. It then transfers control to the generated sequence. The generated code sequence is almost identical to the original one, but Pin ensures that it regains control when a branch exits the sequence. After regaining control, Pin generates more code for the branch target and continues execution. Pin makes this efficient by keeping all of the generated code in memory so it can be reused and directly branching from one sequence to another. In JIT mode, the only code ever executed is the generated code. The original code is only used for reference. When generating code, Pin gives the user an opportunity to inject their own code (instrumentation).

DynamoRIO

DynamoRIO is a runtime code manipulation system that supports code transformations on any part of a program, while it executes. DynamoRIO exports an interface for building dynamic tools for a wide variety of uses: program analysis and understanding, profiling, instrumentation, optimization, translation, etc. Unlike many dynamic tool systems, DynamoRIO is not limited to insertion of callouts/trampolines and allows arbitrary modifications to application instructions via a powerful IA-32/AMD64 instruction manipulation library. DynamoRIO provides efficient, transparent, and comprehensive manipulation of unmodified applications running on stock operating systems (Windows or Linux) and commodity IA-32 and AMD64 hardware.

For ARM, see also DynamoRIO-ARM and (dead?) DynamoRIO-for-ARM

TEMU

The BitBlaze infrastructure provides a component, called TEMU, for dynamic binary analysis. TEMU is built upon a whole-system emulator, QEMU, and provides the following functionality:

  • Dynamic taint analysis. TEMU is able to perform whole-system dynamic taint analysis. Marking certain information sources (e.g., keystrokes, network inputs, reads for certain memory locations, and function call outputs) as tainted, TEMU keeps track of the tainted information propagating in the system. This feature also provides a plug-in environment for dynamic symbolic execution, in which symbolic values are marked as tainted, and concrete values as untainted.
  • OS awareness. Information about OS-level abstractions like processes and files is important for many kinds of analysis. Using knowledge of the guest operating system (Windows XP or Linux), TEMU can determine what process and module is currently executing, what API calls have been invoked (with their arguments), and what disk locations belong to which files.
  • In-depth behavioral analysis. TEMU is able to understand how an analyzed binary interacts with the environment, such as what API calls are invoked, and what outstanding memory locations are accessed. By marking the inputs as tainted (i.e., symbolic), TEMU provides insights about how outputs are formulated from inputs.

QIRA

QEMU Interactive Runtime Analyser to do dynamic analysis as well as IDA does static analysis
Write-up example: ezhp

Vdb/Vtrace / Vivisect

  • debugger, static analysis
  • Windows, Linux, Android
  • Intel, ARM

vtrace is a cross-platform process debugging API implemented in python, and vdb is a debugger which uses it
vivisect is a Python based static analysis and emulation framework

Android

ADBI: Binary Instrumentation Framework for Android

Slides here

Dynamic Dalvik Instrumentation Framework for Android

Slides here

DroidScope

DECAF(short for Dynamic Executable Code Analysis Framework) is a binary analysis platform based on QEMU. This is also the home of the DroidScope dynamic Android malware analysis platform. DroidScope is now an extension to DECAF
Slides here and article here

DroidBox

Android Application Sandbox

TaintDroid

Realtime Privacy Monitoring on Smartphones

Soot

Java, Dalvik (see here and here)

GameCIH

GameGuardian

Drozer

Comprehensive security and attack framework for Android
Interacts with Dalvik VM and explore applications attack surface (activities, content providers, services, etc).
Can also be used remotely à la Metasploit with exploits & payloads

AndBug

A Scriptable Debugger for Android's Dalvik Virtual Machine

Hooker

Hooker is an opensource project for dynamic analysis of Android applications. This project provides various tools and applications that can be use to automaticaly intercept and modify any API calls made by a targeted application. It leverages Android Substrate framework to intercept these calls and aggregate all their contextual information (parameters, returned values, ...) in an elasticsearch database. A set of python scripts can be used to automatize the execution of an analysis in order to collect any API calls made by a set of applications.

Xposed

Changes app_process binary and hooks into all system or applications
Many modules
See also XDA forum

Cydia Substrate

Similar to Xposed but not via replacement of system components.
Hooks into Dalvik and native code

Misc

More tools at http://wiki.secmobi.com/tools:android_dynamic_analysis

Java

Javasnoop

A tool that lets you intercept methods, alter data and otherwise hack Java applications running on your computer.

ELF

ltrace/strace

Tracing library calls and system calls.
Getting a summary: 

ltrace -f -S mybin 2>&1|grep '(.*)'|sed 's/(.*//'|sort|uniq -c

Getting more: 

ltrace -f -i -S -n 4 -s 1024 mybin

ftrace

Tracing inner execution flow as well

Lib preloading

#define _GNU_SOURCE

#include <dlfcn.h>
#include <sys/types.h>
#include <unistd.h>
#include <errno.h>
#include <stdio.h>
#include <time.h>


// Kill nanosleep()
int nanosleep(const struct timespec *req, struct timespec *rem){
    printf("\n==== In our own nanosleep(), I dunnah want sleep\n");
    return 0;
}

// Kill usleep()
int usleep(useconds_t usec){
    printf("\n==== In our own usleep(), I dunnah want sleep\n");
    return 0;
}

// Fix time()
time_t time(time_t *t){
    printf("\n==== In our own time(), will return 1380120175\n");
    return 1380120175;
}

// Fix srand()
void srand(unsigned int seed){
    printf("\n==== In our own srand(), will do srand(0)\n");
    void (*original_srand)(unsigned int seed);
    original_srand = dlsym(RTLD_NEXT, "srand");
    unsigned int myseed = 0;
    return (*original_srand)(myseed);
}

#if 0
// Kill rand()
int rand(void){
    printf("\n==== In our own rand(), will return 0\n");
    return 0;
}
#else
// Intercept rand()
int rand(void){
    int (*original_rand)(void);
    original_rand = dlsym(RTLD_NEXT, "rand");
    int r = (*original_rand)();
    printf("\n==== In our own rand(), will return %04X\n", r);
    return r;
}
#endif

gcc -fPIC -shared -Wl,-soname,patch -o patch.so patch.c -ldl
export LD_PRELOAD=patch.so
export LD_LIBRARY_PATH=.:$LD_LIBRARY_PATH

ldpreloadhook

a quick open/close/ioctl/read/write/free symbol hooker

injectso

  • x86-32, x86-64, ARM (since v0.52)

scanmem

scanmem is a simple interactive debugging utility for linux, used to locate the address of a variable in an executing process. This can be used for the analysis or modification of a hostile process on a compromised machine, reverse engineering, or as a "pokefinder" to cheat at video games.

  • Linux/Android
  • with a GUI since v0.13: GameConqueror

GDB

Enable binary writing, here changing a conditional jump to unconditional jump: 

gdb -write -silent --args mycode 1 2 3
...
(gdb) set {unsigned char}0x400123 = 0xeb
(gdb) disassemble 0x400123 0x400124
0x400123 jmp 0x...

or injecting NOPs: 

(gdb) set {unsigned char}0x400123 = 0x90

Extensions

Stephen Bradshaw ha swritten some extensions to have more useful gdb info when debugging stripped binaries, closer to what you get with OllyDbg. See:

GUI

  • Voltron is an unobtrusive debugger UI for hackers
  • SchemDBG is a backend agnostic debugger frontend that focuses on debugging binaries without access to the source code

ERESI

The ERESI Reverse Engineering Software Interface is a multi-architecture binary analysis framework with a domain-specific language tailored to reverse engineering and program manipulation.

PE

Process Monitor

Process Explorer

RegShot

Computes diff between two registry snapshots

HeapMemView

OllyDbg

PE32-only dynamic disassembler and debugger: http://ollydbg.de/.
Version 1.1 is historically widespread, version 2.0 is re-written from scratch, still considered as beta by some.
Support software and hardware breakpoint, binary patching and repacking, symbol analysis, advanced instruction pattern search, trace with conditional breaking, etc.

ImmDbg

There is also a patched version of OllyDbg with advanced python scripting ability called Immunity Debugger: http://www.immunityinc.com/products-immdbg.shtml
Expect some OllyDbg plugins to not work properly with ImmDbg.
Plugins:

  • Mona, a debugger plugin / Exploit Development Swiss Army Knife

WinAppDbg

The WinAppDbg python module allows developers to quickly code instrumentation scripts in Python under a Windows environment.

Tracer.py

Based on WinAppDbg, finds interesting bits in trace by dichotomy signal/noise

  • run first time and try everything but not the interesting stuff -> use noise option
  • then run again and try interesting stuff -> use signal option

WTFDLL.py

Find libraries loaded at runtime and the functions called

Cuckoo Sandboxing

Currently only supporting Windows binaries.
Cuckoo Sandbox is a malware analysis system. You can throw any suspicious file at it and in a matter of seconds Cuckoo will provide you back some detailed results outlining what such file did when executed inside an isolated environment. Cuckoo generates a handful of different raw data which include:

  • Native functions and Windows API calls traces
  • Copies of files created and deleted from the filesystem
  • Dump of the memory of the selected process
  • Full memory dump of the analysis machine
  • Screenshots of the desktop during the execution of the malware analysis
  • Network dump generated by the machine used for the analysis

Dynamic protections

Patching

Exploitation

Tools

  • ROPgadget, supports ELF/PE/Mach-O format on x86, x64, ARM, PowerPC, SPARC and MIPS architectures
  • ROPshell, online, supports ELF/PE/Mach-O format on x86, x64, ARM
  • pwntools
  • PEDA: Python Exploit Development Assistance for GDB (x86/x64)
  • GEF: GDB enhanced features - multi-arch (x86/x64/mips/ppc/arm)
  • Hexcellents notes
  • ROP on ARM (pdf) by Xipiter / dontstuffbeansupyournose
  • Framing Signals a return to portable shellcode: article, slides

Mitigation techniques

Some are taken from excellent Android Hacker's Handbook

Hardening the Heap

Hardened version of dlmalloc? Alternatives?

This can be done with LD_PRELOAD, e.g. with tcmalloc 

LD_PRELOAD="/usr/lib/libtcmalloc.so"

Protecting against Integer Overflows

  • Protected calloc?
  • Hardened library for safe integer operations: safe_iop

Preventing Data Execution

Set stack (and heap) as non-executable.
Kernel marks stack as executable unless it finds a GNU_STACK program header without executable flag set.
To insert non-exec statement: 

flag: -znoexecstack


To test: 

/usr/sbin/execstack -q myprog
  • "?": myprog has no GNU_STACK -> stack is executable
  • "-": stack non-executable
  • "X": stack executable

Same: 

readelf -a myprog|grep -A1 GNU_STACK
  • present? with RW or RWE?

Same: 

cat /proc/123/maps|grep -E '(stack|heap)'
  • rw or rwx?

To modify existing bin: 

/usr/sbin/execstack -s myprog # set executable stack
/usr/sbin/execstack -c myprog # clear

Max nr of process IDs

/sbin/sysctl kernel.pid_max

Traditionally 32768 

/sbin/sysctl -w kernel.pid_max=4194303

ptrace

/sbin/sysctl kernel.yama.ptrace_scope

To allow ptrace: 

/sbin/sysctl -w kernel.yama.ptrace_scope=0

Address Space Layout Randomization

Bin needs to be compiled position-independent: 

CFLAGS: -fPIE
LDFLAGS: -pie

To test: 

readelf -h myprog | grep Type:
  • DYN? position-independent
  • EXEC? Not position-independent

or 

readelf -d myprog | grep TEXTREL

Global settings 

/sbin/sysctl kernel.randomize_va_space
/sbin/sysctl -w kernel.randomize_va_space=2
  • 0 – No randomization. Everything is static.
  • 1 – Conservative randomization. Shared libraries, stack, mmap(), VDSO and heap are randomized.
  • 2 – Full randomization. In addition to elements listed in the previous point, memory managed through brk() is also randomized.

To disable it locally (in a bash and its children) 

setarch `uname -m` -R /bin/bash

On 32 bit systems “ulimit -s unlimited” disables the randomization of the mmap()-ing

Protecting the Stack

ProPolice stack protection is enabled by using 

flags: -fstack-protector

Format String Protections

Enabled by using 

flags: -Wformat-security -Werror=format-security

Beware compiler cannot detect all corner cases
See also _FORTIFY_SOURCE=2 for runtime protection against %n

Read-Only Relocations

Partial relro enabled by using 

flags: -Wl,-z,relro

To test: 

readelf -h myprog|grep RELRO
  • GNU_RELRO? Partial relro protection present

Full relro enabled by using 

flags: -Wl,-z,relro -Wl,-z,now

To test: 

readelf -d myprog|grep NOW
  • flags NOW? Full relro protection present

Access Control Mechanisms

SELinux

Static source code analysis and fortifying

cppcheck

cppcheck --quiet --check-config .
cppcheck --xml --xml-version=2 --std=posix --std=c99 \
  --enable=style,performance,portability,information,unusedFunction \
  -I include --force --inconclusive .

flawfinder

flawfinder --quiet --dataonly --singleline --followdotdir .|sort -k 2 -r|less
flawfinder --immediate --dataonly --inputs --followdotdir .

gcc/clang

export CFLAGS="-Wall -g -O2 -Wextra -pipe -funsigned-char -fstrict-aliasing -Wchar-subscripts -Wundef -Wshadow -Wcast-align -Wwrite-strings -Wunused -Wuninitialized -Wpointer-arith -Wredundant-decls -Winline -Wformat -Wformat-security -Wswitch-enum -Winit-self -Wmissing-include-dirs -Wmissing-prototypes -Wstrict-prototypes -Wold-style-definition -Wbad-function-cast -Wnested-externs -Wmissing-declarations "

Clang: 

export CFLAGS="-Wunreachable-code"
export CFLAGS="$CFLAGS -fno-omit-frame-pointer -D_FORTIFY_SOURCE=2 -fstack-protector"
export LDFLAGS="$LDFLAGS -fsanitizer=address -fno-omit-frame-pointer -D_FORTIFY_SOURCE=2 -fstack-protector"
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