Transparent proxy UDP

 Uncategorized  No Responses »
Fév 172019
 

In a previous article, we had built a transparent proxy for tcp (outbound) connections.

In short any tcp outbound connection on port_x would be redirected to ip:port_z.

Main usage was to implement a transparent proxy for http traffic (applications would « transparently » be redirected to a proxy accepting « intercepted » traffic).

This time, lets do the same for (outbound) UDP.

One possible scenario : intercept all outbound dns traffic and redirect to another dns server.

Syntax:

proxy-udp 1.0 by erwan2212@gmail.com
proxy-udp original_port new_port new_ip [local]
remember that if you divert to a local app, this local app could be diverted as well.

Example : proxy-udp 53 53 192.168.1.144 local
With a rogue dns server running locally (skip the ‘local’ if the rogue server is running on another host).

Note the warning about diverting to a local app.
For instance, you could be running your local rogue server locally but then since this rogue server will also perform dns queries, you would end up in catch 22 situation.
Possible workarounds :
-have your rogue server « escape » the filter and use a remote udp port different than the filtered one (i.e something different than 53) OR a different protocol (i.e something different than UDP)
-review the code and filter on the original dns server
-review the code and exclude the dns server used by the rogue server

Source code and binaries can be found on my github.

Build a lightweigth HTTPS server : step 1

 delphi  1 Response »
Fév 172019
 

Lets install Indy 10 in Lazarus.
Lazarus has this cool feature called Online Package Manager (OPM).

If you cannot find it under Package menu, go to package\install/uninstall package and move it from right column (availabe) to left column (install).

https://imgur.com/snlW7D5

Save and rebuild ide, and restart.

Now, go to OPM and install Indy and you are done : never been so easy 🙂

https://imgur.com/gxafmAz

Build a lightweigth HTTPS server

 delphi  1 Response »
Fév 172019
 

In the next 4 articles we will see how to build a lightweight HTTPS server which can be used in some situations to troubleshoot/test.

Step 1 : we will install Indy 10 in Lazarus
Step 2 : we will code a lightweight http server
Step 3 : we will generate a root certificate authority / use it to sign a certificate and turn our http server in https
step 4 : we will see the difference between CN field (normally matching your web server) and SAN field (nowadays required by modern browsers)

Transparent TCP proxy

 network  1 Response »
Fév 032019
 

Still playing with Windivert (see original article here), I this time decided to code a transparent proxy.

Principle is the following : divert a destination port (say tcp:80) to a new destination_ip:port.

On the destination ip, i am running privoxy (but any proxy supporting transparent mode would do).
In privoxy config file, I am setting accept-intercepted-requests=1 .

This will be completely transparent for the source application.

Nothing really fancy in the code except may be me storing the orginal remote ip (which we will need to re apply on the traffic back) in an array dynamic_source_port=remote_ip.

Source code and binaries can be found here.

TCPRedir

 network  No Responses »
Jan 272019
 

In a previous article, I did comment on a nice opensource library (Windivert) and shared a basic freepascal demo to use it.

This time I used this library to redirect (or reuse) a local port used by another application or service to another local port.

It could be handy to fool firewalls or to hijack traffic going to a service.

One of the best example that come to my mind is to redirect local port 445 to a an application/shell of your own listening on local port 1337.
Something you could not achieve like netsh port redirect as the port is already in use and/or used by a kernel service (SMB in our case).

The command line would then be tcpredir 445 1337.

Source code and binaries on Github.

One possible application example:

-divert local port 445 to port 1337
-set up a smb server on port 1337

https://i.imgur.com/kSCrC9M.png

Windivert : a user-mode packet capture-and-divert package for Windows

 network  4 Responses »
Jan 272019
 

Quoting the original web site (here) :

Windows Packet Divert (WinDivert) is a user-mode packet capture-and-divert package for Windows 2008, Windows 7, Windows 8, Windows 10 and Windows 2016.

WinDivert allows user-mode applications to capture/modify/drop network packets sent to/from the Windows network stack. In summary, WinDivert can:

capture network packets
filter/drop network packets
sniff network packets
(re)inject network packets
modify network packets
WinDivert can be used to implement user-mode packet filters, packet sniffers, firewalls, NAT, VPNs, tunneling applications, etc.

The main features of WinDivert include:

packet interception, sniffing, or dropping modes
supports loopback (localhost) traffic
full IPv6 support
network layer
simple yet powerful API
high-level filtering language
filter priorities
silent installation
freely available under the terms of the GNU Lesser General Public License (LGPL)

Similar to the raw socket sniffer (here), i have shared a demo (in freepascal) here.

Because windivert is a kernel driver, issues inherent to the windows raw sockets will not apply here.

CloneDisk : do a live backup of a volume

 clonedisk  1 Response »
Jan 212019
 

You have this volume you want to backup but this is a live volume : some apps are constantly writting to it and you need to backup a snapshot.

Lets use CloneDisk and VSCSC

On the command line :
-Lets create a volume shadow copy : vscsc.exe -wait f:
In CloneDisk :
-lets assign a x: logical drive letter to our shadow volume copy (step 1 below) -> this step is optional
-lets backup this x: logical drive, or dosdevice if you did not assign a letter, to a file (step 2 below)

You can now restore from this file but also open it in 7zip, mount it with imdisk, etc.

DNSPING v0.6

 network  No Responses »
Jan 062019
 

A slight update to previous version.

Syntax now is


dnsping 0.6 by erwan2212@gmail.com
usage: dnsping query nameserver query
usage: dnsping query nameserver query delay_seconds
usage: dnsping cache
usage: dnsping flush
usage: dnsping add nameserver hostname ip
usage: dnsping delete nameserver hostname ip

Additions are : cache & flush, add & delete (against a MS DNS server).

Download here.

Source code is here.

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