Understanding Bash STDOUT / STDERR using Hping3

Commands run on bash prompt can output content to standard output (STDOUT) and standard error (STDERR)

If you wish to suppress some data, it can be done by redirecting content from either sources to /dev/null. Alternate notations for the above are :



/dev/null refer to the Null Device File that discards all data written to it (http://en.wikipedia.org/wiki/Null_device)

Taking the example of hping3, we can see different outputs as below

The default output of hping3 is sent to both STDOUT and STDERR. The ping responses are sent to the STDOUT, whereas the packet summary/statics is sent to STDERR

Default Output

Default Output

When we send the output from hping3 to /dev/null, only the STDOUT is sent to /dev/null. The other part of the output is not sent to /dev/null as it is actually sent to STDERR

STDOUT to /dev/null

STDOUT to /dev/null

If we want to send the STDERR to /dev/null, we can do the same using the notation 2> . As mentioned earlier the integer notation for STDERR is ‘2’. Thus ‘2>’ represents redirecting STDERR to non-standard location.

STDERR to /dev/null

STDERR to /dev/null

If you don’t want any output from a command, you can simply redirect STDERR to STDOUT which in-turn is redirected to /dev/null

Both STDERR and STDOUT to /dev/null

Both STDERR and STDOUT to /dev/null

If in some weird use-case you wish to push everything to STDERR, it can be done using 1>&2



Knowing how to redirect STDOUT and STDERR is very useful when scripting in bash.

Hacking Guest Wifi Networks

(Cross-posting from my organization’s blog – http://niiconsulting.com/checkmate/2014/03/insecure-implementation-guest-wireless-networks/)

Most large organizations provide wireless facilities for their guest, which may include vendors, consultants, business associates, employees from other regions etc.

Certain points should be considered while implementing a guest wireless network.

  1. Encryption in use
  2. Captive Portals or Guest Authentication
  3. Network Segregation

Finding the SSID of a Hidden wireless network

To simplify the connectivity for guest devices some organizations configure their networks without encryption i.e. ‘OPEN’. To prevent un-authorized entities from connecting to their networks most of these networks are configured as HIDDEN. As is well known, this configuration does not really provide any security. It is simply a method of obfuscation (Non-Broadcast Wireless SSIDs Why hidden wireless networks are a bad idea).

To identify the SSID of a hidden network you would need:

  1. Wireless adapter which supports packet injection (http://www.aircrack-ng.org/doku.php?id=compatible_cards)
  2. Aircrack-ng wireless suite (http://www.aircrack-ng.org/)

I will be using an Alfa AWUS036H adapter. This card is well supported by Aircrack-ng.

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Does Your DLP/IRM Implementation Keep You Awake At Night?

With the fragmented manner of work culture in the 21st century, organizations have started to wake up to a fact that they cannot withhold information within the confines of their heavily guarded data-centers. Clients, employees and vendors need the information to continue smooth functioning of their businesses.

Information usually falls into anyone of the below categories:

Classification Legitimate Users Examples
Public  Visible to everyone in the world Tender documents
Internal Only for employees Memos, newsletters
Restricted Only for certain people/teams Contracts, Invoices, PO, Network Diagrams
Confidential Sensitive information – for very specific people Financial proposal
Private personal information of people Salaries, Employee HR Information

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How-to: Modify Apache-Coyote/1.1 Banner

If you’ve ever done a penetration test or got one done, you may have come across the following scenario:

HTTP Service running on port 8080, revealing the version information of the product in it banner.
The banner  revealed is Apache-Coyote/1.1.
This is the banner of the Apache Tomcat Web Server which runs on port 8080 by default.

Apache-Coyote/1.1 Version Disclosure

Now, as per good security practice, the banner should be removed or modified, so that it no longer reveals the version number.
This can be achieved by editing your server.xml configuration file found at the below location:


Original server.xml reveals version information

Modified server.xml

You may need to restart your server for the changes to reflect.
Once the Tomcat server is up, test the server to see if it shows the custom header.


> telnet localhost 8080

Web Server with Custom HTTP Banner


Hope this helps others who are looking for a solution to the banner version disclosure

Check out OWASP’s article on Securing Tomcat for more details.


Vulnerable Web Applications for learning

Update: 08/08/2010: Created a tabled output of the listing. Platforms for most applications added. More applications added to list thanks to comments.

Just a quick post. Someone on the ‘NULL’ mailing asked for WebGoat alternatives to learning Web Application penetration testing. The reponse was amazing, with many applications being listed as vulnerable web applications designed for learning web-app pentest. I have collected  all vulnerable web applications and listed them below for reference:

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[Tool] Unique Pattern Generator for Exploit Development

CAUTION: I have realised, that this script gives wrong results after a certain length of characters. It’s not recommended for use. The intention for this script was for me to learn some coding – which I have. But I haven’ got the time at the moment to fix the errors. Hopefully, sometime in the future, I’ll be able to re-write the code. You can use corelanc0d3r’s pvefindaddr.py, which is an excellent script for Immunity Debugger.

Update: Thanks to corelanc0d3r for pointing out that my script does not generate an output same as the metasploit and pvefindaddr scripts. This is useful, as pointed by him, to anyone wishing to mix the outputs/offsets between the tools. I have made relevant changes to the code and also fixed another bug which prevented all offsets from being calculated.

While developing exploits, at times you require a unique string for which any 4 consecutive characters selected at an instance are unique across the string(or may be repeated only after a large gap of characters). This is mostly used to find the ‘offset’ of the characters which have over-written the EIP register.

Metasploit (version 3.0+) has a tool for both:
1) to generate the string pattern (tools/pattern_create.rb)
2) to find the offset of the required pattern (tools/pattern_offset.rb)
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