CAPEC-139 Relative Path Traversal

An attacker exploits a weakness in input validation on the target by supplying a specially constructed path utilizing dot and slash characters for the purpose of obtaining access to arbitrary files or resources. An attacker modifies a known path on the target in order to reach material that is not available through intended channels. These attacks normally involve adding additional path separators (/ or \) and/or dots (.), or encodings thereof, in various combinations in order to reach parent directories or entirely separate trees of the target's directory structure.

1. [Explore] [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. 2. [Explore] [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. 3. [Experiment] [Attempt variations on input parameters] Using manual or automated means, an adversary attempts varying relative file path combinations on all found user input locations and observes the responses. 4. [Exploit] [Access, modify, or execute arbitrary files.] An adversary injects 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.

• The target application must accept a string as user input, fail to sanitize combinations of characters in the input that have a special meaning in the context of path navigation, and insert the user-supplied string into path navigation commands.

• [Low] To inject the malicious payload in a web page • [High] To bypass non trivial filters in the application

• Integrity: Modify Data • Confidentiality: Read Data • Confidentiality, Integrity, Availability: Execute Unauthorized Commands • Access Control: Bypass Protection Mechanism • Availability: Unreliable Execution

• Design: Input validation. Assume that user inputs are malicious. Utilize strict type, character, and encoding enforcement • Implementation: Perform input validation for all remote content, including remote and user-generated content. • Implementation: Validate user input by only accepting known good. Ensure all content that is delivered to client is sanitized against an acceptable content specification -- using an allowlist approach. • Implementation: Prefer working without user input when using file system calls • Implementation: Use indirect references rather than actual file names. • Implementation: Use possible permissions on file access when developing and deploying web applications.