Skip to main content

TcpDumpTutorial

When using a tool that displays network traffic a more natural (raw) way the burden of analysis is placed directly on the human rather than the application. This approach cultivates continued and elevated understanding of the TCP/IP suite, and for this reason I strongly advocate using tcpdump instead of other tools whenever possible.

An anagram for the TCP flags: Unskilled Attackers Pester RealSecurity Folk ]
Show me all URGENT (URG) packets...
# tcpdump 'tcp[13] & 32!=0'

Show me all ACKNOWLEDGE (ACK) packets...
# tcpdump 'tcp[13] & 16!=0'

Show me all PUSH (PSH) packets...
# tcpdump 'tcp[13] & 8!=0'

Show me all RESET (RST) packets...
# tcpdump 'tcp[13] & 4!=0'

Show me all SYNCHRONIZE (SYN) packets...
# tcpdump 'tcp[13] & 2!=0'

Show me all FINISH (FIN) packets...
# tcpdump 'tcp[13] & 1!=0'

Show me all SYNCHRONIZE/ACKNOWLEDGE (SYNACK) packets...
# tcpdump 'tcp[13]=18'
[ Note: Only the PSH, RST, SYN, and FIN flags are displayed intcpdump's flag field output. URGs and ACKs are displayed, but they are shown elsewhere in the output rather than in the flags field ]
Keep in mind the reasons these filters work. The filters above find these various packets because tcp[13] looks at offset 13 in the TCP header, the number represents the location within the byte, and the !=0 means that the flag in question is set to 1, i.e. it's on.
As with most powerful tools, however, there are multiple ways to do things. The example below shows another way to capture packets with specific TCP flags set.
Capture TCP Flags Using the tcpflags Option...
# tcpdump 'tcp[tcpflags] & & tcp-syn != 0'

Comments

Popular posts from this blog

Hacking Windows 10 UWP App: DLL Injection & common Vulnerabilities

I recently started working on  widows 10 Apps( Apps not Applications) security. Before diving deep in hacking terms lets try to understand what's new in Windows 10 UWP( Universal Platform) as compared to old Apps. Lets begin with how apps actually work on windows 10(desktop/tablet). Now windows 10 comes with a container only for running apps inside the isolated environment. By default, /APPCONTAINER(Linker Flag) is off. This option modifies an executable to indicate whether the app must be run in the appcontainer process-isolation environment. Specify /APPCONTAINER for an app that must run in the appcontainer environment—for example, a Windows Store app. (The option is set automatically in Visual Studio when you create a Windows Store app from a template.) For a desktop app, specify /APPCONTAINER:NO or just omit the option. The /APPCONTAINER option was introduced in Windows 8. Now there is no registry entry concept for these app in the System HIVE rather they install they own hiv

Jsunpack-n Tutorial (Analyzing Malicious Documents)

INSTALLATION: Required Dependencies(all these dependencies are present in jsunpack-n package in a folder named depend): 1) Build and install pynids (nids) from ./depends/pynids-0.6.1.tar.gz To compile pynids, you may need the following (ubuntu) packages: libpcap-dev pkg-config python-dev libgtk2.0-dev libnet1-dev         To install these package either use software center or command apt-get install PackageName     $ cd depends     $ tar xvfz pynids-0.6.1.tar.gz $ cd pynids-0.6.1/ directory $ python setup.py build $ sudo python setup.py install 2) Build SpiderMonkey 'js' from ./depends/js-1.8.0-rc1-src.tar.gz     This package has modifications to the spidermonkey source code; therefore, it is not recommended you use default smjs packages. (Details of the modifications are in INSTALL.spidermonkey.shellcode and INSTALL.spidermonkey, for historical purposes)     $ cd depends/     $ tar xvfz js-1.8.0-rc1-src.tar.gz     $ cd js-1.8.0-rc1-src     $ mak

SSI Injection Attack

SSIs are directives present on Web applications used to feed an HTML page with dynamic contents. They are similar to CGIs, except that SSIs are used to execute some actions before the current page is loaded or while the page is being visualized. In order to do so, the web server analyzes SSI before supplying the page to the user. The Server-Side Includes attack allows the exploitation of a web application by injecting scripts in HTML pages or executing arbitrary codes remotely. It can be exploited through manipulation of SSI in use in the application or force its use through user input fields. It is possible to check if the application is properly validating input fields data by inserting characters that are used in SSI directives, like:  Code: < ! # = / . " - > and [a-zA-Z0-9] Another way to discover if the application is vulnerable is to verify the presence of pages with extension .stm, .shtm and .shtml. However, the lack of these type of pages does not mean that th