threat-modeling.md

Threat Model Analysis for sharkdp/fd

Threat: Inherent Risk of fd Extended Features (-x, -e)

• Description: fd provides powerful features like -x (execute a command for each found file) and -e (use a custom executor). If an application utilizes these features, especially with any degree of dynamic command construction or user-influenced parameters (even indirectly), it introduces a significant risk. An attacker, by manipulating inputs that influence the files fd finds or the parameters passed to the executed command, could potentially inject and execute arbitrary commands on the server. Even if user input doesn't directly construct the command, if it influences the files that fd finds and passes to -x or -e, vulnerabilities can arise if the executed command is not designed to handle arbitrary file paths securely.
• Impact: Arbitrary command execution on the server. This can lead to full system compromise, data breaches, data manipulation, denial of service, or privilege escalation, depending on the command executed and the permissions of the user running fd.
• Affected FD Component: The -x (execute) and -e (executor) options of fd.
• Risk Severity: Critical
• Mitigation Strategies:
  • Avoid -x and -e if possible: The most secure approach is to avoid using these features altogether unless absolutely necessary. Consider alternative approaches to achieve the desired functionality without relying on command execution via fd.
  • Strictly Control Command Construction (if -x or -e are essential): If -x or -e must be used, ensure the command being executed is statically defined and never constructed dynamically based on user input or even indirectly user-influenced data.
  • Input Validation for Executed Commands (if unavoidable dynamic parts): If there are unavoidable dynamic parts in the executed command (which is highly discouraged), rigorously validate and sanitize any data that influences the command or its arguments. Use allow-lists and escape shell metacharacters.
  • Least Privilege for Executed Commands: Ensure the command executed by -x or -e runs with the minimum necessary privileges.
  • Sandboxing/Isolation for Executed Commands: If possible, execute the commands spawned by -x or -e in a sandboxed environment or container to limit the impact of potential vulnerabilities.

Threat: Resource Exhaustion via Complex fd Queries

• Description: fd's search functionality, while efficient in many cases, can become resource-intensive when processing extremely complex queries, very broad search patterns (e.g., highly complex regular expressions or overly broad glob patterns like .* in deep directory structures), or when searching very large file systems. An attacker could intentionally craft such queries to overload the server, causing a denial of service. This is especially relevant if the application allows users to define or influence the search patterns used by fd.
• Impact: Denial of Service (DoS). The application becomes slow or unresponsive, potentially impacting all users. Server overload can affect other applications on the same server. In severe cases, it could lead to system instability or crashes.
• Affected FD Component: fd's core search engine and pattern matching logic when handling complex or broad queries, especially in large file systems.
• Risk Severity: High (can easily lead to service disruption)
• Mitigation Strategies:
  • Timeout Mechanisms for fd Execution: Implement strict timeouts for fd command execution to prevent runaway processes from consuming resources indefinitely.
  • Resource Limits (cgroups, ulimit): Limit the CPU, memory, and I/O resources available to the process executing fd using operating system mechanisms.
  • Input Complexity Limits for Search Patterns: Restrict the complexity of user-provided search patterns. For example, limit the length or complexity of regular expressions, or restrict the depth of directory searches.
  • Rate Limiting for Search Requests: Implement rate limiting on the number of fd search requests from a single user or IP address within a given timeframe.
  • Monitoring and Alerting for Resource Usage: Monitor system resource usage (CPU, memory, I/O) and set up alerts for unusual spikes or sustained high usage related to fd processes.