COMMON ATTACK PATTERN ENUMERATION AND CLASSIFICATIONLive MITRE record
CAPEC-126
Path Traversal
An adversary uses path manipulation methods to exploit insufficient input validation of a target to obtain access to data that should be not be retrievable by ordinary well-formed requests. A typical variety of this attack involves specifying a path to a desired file together with dot-dot-slash characters, resulting in the file access API or function traversing out of the intended directory structure and into the root file system. By replacing or modifying the expected path information the access function or API retrieves the file desired by the attacker. These attacks either involve the attacker providing a complete path to a targeted file or using control characters (e.g. path separators (/ or \) and/or dots (.)) to reach desired directories or files.
Abstraction
Standard
Typical severity
Very High
Likelihood of attack
High
Understand the attack
What is this attack pattern?
An adversary uses path manipulation methods to exploit insufficient input validation of a target to obtain access to data that should be not be retrievable by ordinary well-formed requests. A typical variety of this attack involves specifying a path to a desired file together with dot-dot-slash characters, resulting in the file access API or function traversing out of the intended directory structure and into the root file system. By replacing or modifying the expected path information the access function or API retrieves the file desired by the attacker. These attacks either involve the attacker providing a complete path to a targeted file or using control characters (e.g. path separators (/ or \) and/or dots (.)) to reach desired directories or files.
Execution flow
How does the attack proceed, step by step?
Explore
Fingerprinting of the operating system
In order to perform a valid path traversal, the attacker needs to know what the underlying OS is so that the proper file seperator is used.
Techniques used
- 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 attacker 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 the Application to Identify User-controllable Inputs
The attacker surveys the target application to identify all user-controllable file inputs
Experiment
Vary inputs, looking for malicious results
Depending on whether the application being exploited is a remote or local one, the attacker crafts the appropriate malicious input containing the path of the targeted file or other file system control syntax to be passed to the application
Exploit
Manipulate files accessible by the application
The attacker may steal information or directly manipulate files (delete, copy, flush, etc.)
Requirements
What does the attack require?
Prerequisites
- The attacker must be able to control the path that is requested of the target.
- The target must fail to adequately sanitize incoming paths
Skills required
- Low: Simple command line attacks or to inject the malicious payload in a web page.
- Medium: Customizing attacks to bypass non trivial filters in the application.
Resources required
- The ability to manually manipulate path information either directly through a client application relative to the service or application or via a proxy application.
Impact
What does a successful attack lead to?
Execute Unauthorized Commands
Affected scopes: Integrity, Confidentiality, Availability
Modify Data
Affected scopes: Integrity
Read Data
Affected scopes: Confidentiality
Unreliable Execution
Affected scopes: Availability
Defence
How is it prevented and mitigated?
1
Design: Configure the access control correctly.
2
Design: Enforce principle of least privilege.
3
Design: Execute programs with constrained privileges, so parent process does not open up further vulnerabilities. Ensure that all directories, temporary directories and files, and memory are executing with limited privileges to protect against remote execution.
4
Design: Input validation. Assume that user inputs are malicious. Utilize strict type, character, and encoding enforcement.
5
Design: Proxy communication to host, so that communications are terminated at the proxy, sanitizing the requests before forwarding to server host.
6
Design: Run server interfaces with a non-root account and/or utilize chroot jails or other configuration techniques to constrain privileges even if attacker gains some limited access to commands.
7
Implementation: Host integrity monitoring for critical files, directories, and processes. The goal of host integrity monitoring is to be aware when a security issue has occurred so that incident response and other forensic activities can begin.
8
Implementation: Perform input validation for all remote content, including remote and user-generated content.
9
Implementation: Perform testing such as pen-testing and vulnerability scanning to identify directories, programs, and interfaces that grant direct access to executables.
10
Implementation: Use indirect references rather than actual file names.
11
Implementation: Use possible permissions on file access when developing and deploying web applications.
12
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.
Real world
MITRE example instances
Example instance 1Detail
An example of using path traversal to attack some set of resources on a web server is to use a standard HTTP request
http://example/../../../../../etc/passwd
From an attacker point of view, this may be sufficient to gain access to the password file on a poorly protected system. If the attacker can list directories of critical resources then read only access is not sufficient to protect the system.