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.
Likelihood Of Attack
High
Typical Severity
High
Relationships
This table shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf and ParentOf, and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.
Nature
Type
ID
Name
ChildOf
Standard Attack Pattern - A standard level attack pattern in CAPEC is focused on a specific methodology or technique used in an attack. It is often seen as a singular piece of a fully executed attack. A standard attack pattern is meant to provide sufficient details to understand the specific technique and how it attempts to accomplish a desired goal. A standard level attack pattern is a specific type of a more abstract meta level attack pattern.
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 plug-ins are available to facilitate the analysis or automate the URL discovery.
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.
Techniques
Provide "../" or "..\" at the beginning of any filename to traverse to the parent directory
Use a list of probe strings as path traversal payload. Different strings may be used for different platforms. Strings contain relative path sequences such as "../".
Use a proxy tool to record results of manual input of relative path traversal probes in known URLs.
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.
Techniques
Manipulate file and its path by injecting relative path sequences (e.g. "../").
Download files, modify files, or try to execute shell commands (with binary files).
Prerequisites
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.
Skills Required
[Level: Low]
To inject the malicious payload in a web page
[Level: High]
To bypass non trivial filters in the application
Consequences
This table specifies different individual consequences associated with the attack pattern. The Scope identifies the security property that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in their attack. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a pattern will be used to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
Scope
Impact
Likelihood
Integrity
Modify Data
Confidentiality
Read Data
Confidentiality
Integrity
Availability
Execute Unauthorized Commands
Access Control
Bypass Protection Mechanism
Availability
Unreliable Execution
Mitigations
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.
Example Instances
The attacker uses relative path traversal to access files in the application. This is an example of accessing user's password file.
However, the target application employs regular expressions to make sure no relative path sequences are being passed through the application to the web page. The application would replace all matches from this regex with the empty string.
Then an attacker creates special payloads to bypass this filter:
When the application gets this input string, it will be the desired vector by the attacker.
Related Weaknesses
A Related Weakness relationship associates a weakness with this attack pattern. Each association implies a weakness that must exist for a given attack to be successful. If multiple weaknesses are associated with the attack pattern, then any of the weaknesses (but not necessarily all) may be present for the attack to be successful. Each related weakness is identified by a CWE identifier.
Description
This table shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf and ParentOf, and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.
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