Path Traversal Detection Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching path traversal detection, ported and verified for Python. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your Python project — whether you're validating in a Django view, a FastAPI endpoint, or a standalone data processing script.

Python Implementation

# Path Traversal Detection
# ReDoS-safe | RegexVault — Dev & Systems > File Paths

import re

path_traversal_detection_pattern = re.compile(r'(?:^|[/\\])\.\.[/\\]|(?:^|[/\\])\.[/\\]|(?:^|[/\\])\.\.($)')

def validate_path_traversal_detection(value: str) -> bool:
    return bool(path_traversal_detection_pattern.fullmatch(value))

# Example
print(validate_path_traversal_detection("../etc/passwd"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Dev & Systems > File Paths category and carries a ReDoS-safe certification. That matters for Python developers because particularly important in Python web servers where CPU-bound regex operations can stall concurrent request handling. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

MATCH indicates traversal was found — use as a BLOCK pattern. Normalize paths with realpath() before this check to prevent double-encoding bypass.