CAPEC-126: Path Traversal (Directory Traversal)

Overview

CAPEC-126 (Path Traversal) is a standard-level attack pattern catalogued by MITRE in the Common Attack Pattern Enumeration and Classification (CAPEC). It describes a recurring method attackers use to exploit software weaknesses.

How the attack works

The phases an attacker typically follows to carry out this attack.

Step 1
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.
- 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
Step 2
Explore
[Survey the Application to Identify User-controllable Inputs] The attacker surveys the target application to identify all user-controllable file inputs
Step 3
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
Step 4
Exploit
[Manipulate files accessible by the application] The attacker may steal information or directly manipulate files (delete, copy, flush, etc.)

What the attacker needs

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 skill: Simple command line attacks or to inject the malicious payload in a web page.
Medium skill: 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.

Consequences

What a successful CAPEC-126 attack can achieve.

Execute Unauthorized Commands

Affects: Integrity, Confidentiality, Availability

The attacker may be able to create or overwrite critical files that are used to execute code, such as programs or libraries.

Modify Data

Affects: Integrity

The attacker may be able to overwrite or create critical files, such as programs, libraries, or important data. If the targeted file is used for a security mechanism, then the attacker may be able to bypass that mechanism. For example, appending a new account at the end of a password file may allow an attacker to bypass authentication.

Read Data

Affects: Confidentiality

The attacker may be able read the contents of unexpected files and expose sensitive data. If the targeted file is used for a security mechanism, then the attacker may be able to bypass that mechanism. For example, by reading a password file, the attacker could conduct brute force password guessing attacks in order to break into an account on the system.

Unreliable Execution

Affects: Availability

The attacker may be able to overwrite, delete, or corrupt unexpected critical files such as programs, libraries, or important data. This may prevent the software from working at all and in the case of a protection mechanisms such as authentication, it has the potential to lockout every user of the software.

How to mitigate it

Defenses that reduce the risk of CAPEC-126.

Design: Configure the access control correctly.
Design: Enforce principle of least privilege.
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.
Design: Input validation. Assume that user inputs are malicious. Utilize strict type, character, and encoding enforcement.
Design: Proxy communication to host, so that communications are terminated at the proxy, sanitizing the requests before forwarding to server host.
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.
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.
Implementation: Perform input validation for all remote content, including remote and user-generated content.
Implementation: Perform testing such as pen-testing and vulnerability scanning to identify directories, programs, and interfaces that grant direct access to executables.
Implementation: Use indirect references rather than actual file names.
Implementation: Use possible permissions on file access when developing and deploying web applications.
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.

Examples

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.

The CWE weaknesses that CAPEC-126 exploits.

CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

How this attack relates to others in the CAPEC hierarchy.

Parent

CAPEC-153: Input Data Manipulation

Child

Can precede

CAPEC-664: Server Side Request Forgery

Terminology & mappings

Alternate terms

Directory Traversal

Mapped taxonomies

WASC: Path Traversal (33)
OWASP Attacks: Path Traversal

Frequently asked questions

Common questions about CAPEC-126.

What is CAPEC-126?

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.

How does a Path Traversal attack work?

It typically unfolds over 4 phases. It begins with: [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.

How do you prevent CAPEC-126?

Design: Configure the access control correctly.

What weaknesses does CAPEC-126 target?

CAPEC-126 exploits 1 CWE weakness, including CWE-22 (Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')).

How severe is CAPEC-126?

MITRE rates CAPEC-126 as Very High severity with high likelihood of attack.

References

Attack-pattern data is sourced from the MITRE CAPEC catalog (v3.9). Weakness associations link to the corresponding CWE entries on RadicalNotion.AI.