Execution Flow

Fingerprinting of the operating system: In order to perform a valid path traversal, the adversary needs to know what the underlying OS is so that the proper file seperator is used.

Techniques
Port mapping. Identify ports that the system is listening on, and attempt to identify inputs and protocol types on those ports.
TCP/IP Fingerprinting. The adversary uses various software to make connections or partial connections and observe idiosyncratic responses from the operating system. Using those responses, they attempt to guess the actual operating system.
Induce errors to find informative error messages

Survey application: Using manual or automated means, an adversary will survey the target application looking for all areas where user input is taken to specify a file name or path.

Techniques
Use a spidering tool to follow and record all links on a web page. Make special note of any links that include parameters in the URL.
Use a proxy tool to record all links visited during a manual traversal of a web application. Make special note of any links that include parameters in the URL. Manual traversal of this type is frequently necessary to identify forms that are GET method forms rather than POST forms.
Use a browser to manually explore a website and analyze how it is constructed. Many browser's plug-in are available to facilitate the analysis or automate the URL discovery.

Attempt variations on input parameters: Using manual or automated means, an adversary attempts varying absolute file paths on all found user input locations and observes the responses.

Techniques
Access common files in root directories such as "/bin", "/boot", "/lib", or "/home"
Access a specific drive letter or windows volume letter by specifying "C:dirname" for example
Access a known Windows UNC share by specifying "\\UNC\share\name" for example

Access, modify, or execute arbitrary files.: An adversary injects absolute path traversal syntax into identified vulnerable inputs to cause inappropriate reading, writing or execution of files. An adversary could be able to read directories or files which they are normally not allowed to read. The adversary could also access data outside the web document root, or include scripts, source code and other kinds of files from external websites. Once the adversary accesses arbitrary files, they could also modify files. In particular situations, the adversary could also execute arbitrary code or system commands.

Techniques
Manipulate file and its path by injecting absolute path sequences (e.g. "/home/file.txt").
Download files, modify files, or try to execute shell commands (with binary files).

Absolute Path Traversal