CAPEC-213 - Directory Traversal

An attacker with access to file system resources, either directly or via application logic, will use various file path specification or navigation mechanisms such as ".." in path strings and absolute paths to extend their range of access to inappropriate areas of the file system. The attacker attempts to either explore the file system for recon purposes or access directories and files that are intended to be restricted from their access. Exploring the file system can be achieved through constructing paths presented to directory listing programs, such as "ls" and 'dir', or through specially crafted programs that attempt to explore the file system. The attacker engaging in this type of activity is searching for information that can be used later in a more exploitive attack. Access to restricted directories or files can be achieved through modification of path references utilized by system applications.

Severity

Likelihood

Confidentiality

Integrity

Availability

  • Scopes 4
  • Execute unauthorized code or commands
  • Availability
  • Confidentiality
  • Integrity
  • Modify files or directories
  • Integrity
  • Read files or directories
  • Confidentiality
  • DoS: crash / exit / restart
  • Availability

Low level: Simple command line attacks.

Medium level: Programming attacks.

The target must leverage and access an underlying file system.

The attacker must have access to an application interface or a direct shell that allows them to inject directory strings and monitor the results.

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 -- whitelisting approach.