Due to the modular structure of payload stages its pretty trivial
to add DNS resolution instead of hard-coded IP address in stage0.
The only real complication here is that ReverseConnectRetries ends
up being one byte further down than in the original shellcode. It
appears that the original rev_tcp_dns payload suffers from the same
issue.
Hostname substitution is handled in the same method as the RC4 and
XOR keys, with an offset provided and replace_vars ignoring the
hostname.
Tested in x86 native and WOW64 on XP and 2k8r2 respectively.
This is a good option for those of us needing to leave persistent
binaries/payloads on hosts for long periods. Even if the hostname
resolves to a malicious party attempting to steal our hard earned
session, they'd be hard pressed to crypt the payload with the
appropriate RC4 pass. So long as we control the NS and records, the
hardenned shellcode should provide a better night's sleep if running
shells over the WAN. Changing the RC4 password string in the
shellcode and build.py should reduce the chances of recovery by RE.
Next step will likely be to start generating elipses for ECDH SSL
in meterpreter sessions and passing them with stage2 through the
RC4 socket. If P is 768-1024 the process is relatively quick, but
we may want to precompute a few defaults as well to have 2048+.
The HttpOpenRequest function from WinINet requires the
INTERNET_FLAG_KEEP_CONNECTION flag to communicate through an
authenticated proxy.
From MSDN ( http://tinyurl.com/chwt86j ):
"Uses keep-alive semantics, if available, for the connection. This
flag is required for Microsoft Network (MSN), NT LAN Manager (NTLM),
and other types of authentication."
Without this flag, the HTTP stager will fail when faced with a proxy
that requires authentication. The Windows HTTPS stager does not have
this problem.
For HTTP Meterpreter to communicate through an authenticated proxy a
separate patch will need to be made to the Meterpreter source code.
This is at line 1125 of source/common/core.c in the Meterpreter source
code.
My motivation for this request is for windows/dllinject/reverse_http
to download a DLL even when faced with an authenticated proxy. These
changes accomplish this.
Test environment:
I staged a SmoothWall device with the Advanced Proxy Web Add-on. I
enabled Integrated Windows Authentication with a W2K3 DC. I verified
the HTTP stager authenticated to and communicated through the proxy
by watching the proxy access.log
ESI is not clobbered; no need to clear EDX as only DL is filled before and
it is overwritten before use.
Shellcodes in ruby modules not regenerated, but I guess you want to
regenerate them again anyway :-)
Those stagers will encrypt the initial stage with a 128-bit RC4 key and
the stage length with a XOR key. Both keys are embedded in the stager.
This should provide good evasion capabilities in addition to some
protection against MITM reversing (if the stager is sent a different
route, like in an executable on an USB key).
Note that, from a cryptanalyst's standpoint, it is a bad idea to reuse the
same stager (or stagers with the same RC4 and XOR keys) more than once
since an identical key will result in an identical keystream and make
correlation attacks easy. But I doubt that matters in practice.
Also note that since communication after the initial statging is not
encrypted, these stagers should be used in combination with additional
encryption support in the payloads (like Meterpreter).
Provided as a block to be included into stagers and/or decoder stubs.
Also included is a test shellcode that can be used for verifying that the
algorithm is compatible to Ruby's OpenSSL RC4 algorithm.
Ryan Wincey
Alexandre Maloteaux
corelanc0d3r
Tod Beardsley
agix
James Lee
RageLtMan
Raphael Mudge
Michael Schierl
HD Moore
HD Moore
scriptjunkie
Matt Buck
Stephen Fewer
James Lee