Path Traversal in AI Agent File Tools

Path traversal attacks manipulate file paths to escape the intended directory scope. When an AI agent has file system tools, an attacker can influence the agent to access files outside its authorized workspace using relative path sequences like ../ or symlink following.

The Attack

An agent with a file reading tool restricted to /workspace/ receives a request to read ../../../etc/passwd. If the tool naively joins the workspace path with the requested filename, the resulting path resolves outside the workspace to a sensitive system file.

Agents are especially susceptible because they construct file paths from natural language. A user asking "read the configuration file at ../../config/secrets.yaml" might cause the agent to generate a path traversal attempt without recognizing the security implication.

Common Variants

Dot-dot-slash sequences are the classic traversal technique. Multiple ../ segments climb up the directory tree.

URL encoding disguises traversal sequences. %2e%2e%2f decodes to ../ and may bypass string-matching filters.

Null byte injection terminates the path early in some languages, stripping appended suffixes like file extensions.

Symlink following creates a symbolic link inside the authorized directory that points outside it. If the agent follows symlinks, it escapes the sandbox.

Defense Strategies

Canonicalize paths. Resolve the full canonical path using the operating system's path resolution. Then verify the canonical path starts with the authorized base directory. This catches all forms of relative path traversal.

Reject relative components. Authensor's policy engine rejects file paths containing .., and the file system tool should independently enforce this as well.

Disable symlink following. Open files with options that prevent symlink traversal. Check that intermediate directory components are not symlinks pointing outside the sandbox.

Chroot or container isolation. Run the agent in a filesystem namespace where the sandbox root is the actual root. Path traversal cannot escape the namespace boundary.

Policy enforcement. Define allowlisted paths in your Authensor policy. Every file operation is evaluated against the path rules. The policy specifies exactly which directories and file patterns the agent can access.

Monitoring

Alert on any file access attempts that are denied due to path policy violations. These indicate either misconfiguration or active exploitation. Authensor's audit trail records the requested path and the canonical resolved path, making it straightforward to identify traversal attempts.