Writing Data

Radare can manipulate a loaded binary file in many ways. You can resize the file, move and copy/paste bytes, insert new bytes (shifting data to the end of the block or file), or simply overwrite bytes. New data may be give as a widestring, as assembler instructions, or the data may be read in from another file.

Resize the file using the r command. It accepts a numeric argument. A positive value sets a new size for the file. A negative one will truncate the file to the current seek position minus N bytes.

r 1024      ; resize the file to 1024 bytes
r -10 @ 33  ; strip 10 bytes at offset 33

Write bytes using the w command. It accepts multiple input formats like inline assembly, endian-friendly dwords, files, hexpair files, wide strings:

[0x00404888]> w?
|Usage: w[x] [str] [<file] [<<EOF] [@addr]
| w[1248][+-][n]       increment/decrement byte,word..
| w foobar             write string 'foobar'
| w0 [len]             write 'len' bytes with value 0x00
| w6[de] base64/hex    write base64 [d]ecoded or [e]ncoded string
| wa[?] push ebp       write opcode, separated by ';' (use '"' around the command)
| waf file             assemble file and write bytes
| wao[?] op            modify opcode (change conditional of jump. nop, etc)
| wA[?] r 0            alter/modify opcode at current seek (see wA?)
| wb 010203            fill current block with cyclic hexpairs
| wB[-]0xVALUE         set or unset bits with given value
| wc                   list all write changes
| wc[?][ir*?]          write cache undo/commit/reset/list (io.cache)
| wd [off] [n]         duplicate N bytes from offset at current seek (memcpy) (see y?)
| we[?] [nNsxX] [arg]  extend write operations (insert instead of replace)
| wf -|file            write contents of file at current offset
| wh r2                whereis/which shell command
| wm f0ff              set binary mask hexpair to be used as cyclic write mask
| wo[?] hex            write in block with operation. 'wo?' fmi
| wp[?] -|file         apply radare patch file. See wp? fmi
| wr 10                write 10 random bytes
| ws pstring           write 1 byte for length and then the string
| wt[f][?] file [sz]   write to file (from current seek, blocksize or sz bytes)
| wts host:port [sz]   send data to remote host:port via tcp://
| ww foobar            write wide string 'f\x00o\x00o\x00b\x00a\x00r\x00'
| wx[?][fs] 9090       write two intel nops (from wxfile or wxseek)
| wv[?] eip+34         write 32-64 bit value
| wz string            write zero terminated string (like w + \x00)

Some examples:

 [0x00000000]> wx 123456 @ 0x8048300
 [0x00000000]> wv 0x8048123 @ 0x8049100
 [0x00000000]> wa jmp 0x8048320

Write Over

The wo command (write over) has many subcommands, each combines the existing data with the new data using an operator. The command is applied to the current block. Supported operators include: XOR, ADD, SUB...

[0x4A13B8C0]> wo?
|Usage: wo[asmdxoArl24] [hexpairs] @ addr[:bsize]
|Example:
|  wox 0x90   ; xor cur block with 0x90
|  wox 90     ; xor cur block with 0x90
|  wox 0x0203 ; xor cur block with 0203
|  woa 02 03  ; add [0203][0203][...] to curblk
|  woe 02 03  
|Supported operations:
|  wow  ==  write looped value (alias for 'wb')
|  woa  +=  addition
|  wos  -=  substraction
|  wom  *=  multiply
|  wod  /=  divide
|  wox  ^=  xor
|  woo  |=  or
|  woA  &=  and
|  woR  random bytes (alias for 'wr $b'
|  wor  >>= shift right
|  wol  <<= shift left
|  wo2  2=  2 byte endian swap
|  wo4  4=  4 byte endian swap

It is possible to implement cipher-algorithms using radare core primitives and wo. A sample session performing xor(90) + add(01, 02):

[0x7fcd6a891630]> px
- offset -       0 1  2 3  4 5  6 7  8 9  A B  C D  E F  0123456789ABCDEF
0x7fcd6a891630  4889 e7e8 6839 0000 4989 c48b 05ef 1622  H...h9..I......"
0x7fcd6a891640  005a 488d 24c4 29c2 5248 89d6 4989 e548  .ZH.$.).RH..I..H
0x7fcd6a891650  83e4 f048 8b3d 061a 2200 498d 4cd5 1049  ...H.=..".I.L..I
0x7fcd6a891660  8d55 0831 ede8 06e2 0000 488d 15cf e600  .U.1......H.....


[0x7fcd6a891630]> wox 90
[0x7fcd6a891630]> px
- offset -       0 1  2 3  4 5  6 7  8 9  A B  C D  E F  0123456789ABCDEF
0x7fcd6a891630  d819 7778 d919 541b 90ca d81d c2d8 1946  ..wx..T........F
0x7fcd6a891640  1374 60d8 b290 d91d 1dc5 98a1 9090 d81d  .t`.............
0x7fcd6a891650  90dc 197c 9f8f 1490 d81d 95d9 9f8f 1490  ...|............
0x7fcd6a891660  13d7 9491 9f8f 1490 13ff 9491 9f8f 1490  ................


[0x7fcd6a891630]> woa 01 02
[0x7fcd6a891630]> px
- offset -       0 1  2 3  4 5  6 7  8 9  A B  C D  E F  0123456789ABCDEF
0x7fcd6a891630  d91b 787a 91cc d91f 1476 61da 1ec7 99a3  ..xz.....va.....
0x7fcd6a891640  91de 1a7e d91f 96db 14d9 9593 1401 9593  ...~............
0x7fcd6a891650  c4da 1a6d e89a d959 9192 9159 1cb1 d959  ...m...Y...Y...Y
0x7fcd6a891660  9192 79cb 81da 1652 81da 1456 a252 7c77  ..y....R...V.R|w

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