feat(python/django): path traversal rule

rules/python/django/path_traversal.yml

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+imports:
+  - python_shared_lang_dynamic_input
+  - python_shared_lang_import2
+  - python_shared_lang_import4
+patterns:
+  - pattern: $<FILE_SYSTEM_STORAGE>($<...>$<UNSANITIZED_DYNAMIC_INPUT>$<...>)
+    filters:
+      - variable: UNSANITIZED_DYNAMIC_INPUT
+        detection: python_django_path_traversal_dynamic_input
+        scope: result
+      - variable: FILE_SYSTEM_STORAGE
+        detection: python_shared_lang_import4
+        scope: cursor
+        filters:
+          - variable: MODULE1
+            values: [django]
+          - variable: MODULE2
+            values: [core]
+          - variable: MODULE3
+            values: [files]
+          - variable: MODULE4
+            values: [storage]
+          - variable: NAME
+            values: [FileSystemStorage]
+  - pattern: $<DEFAULT_STORAGE>.save($<UNSANITIZED_DYNAMIC_INPUT>, $<...>)
+    filters:
+      - variable: DEFAULT_STORAGE
+        detection: python_shared_lang_import4
+        scope: cursor
+        filters:
+          - variable: MODULE1
+            values: [django]
+          - variable: MODULE2
+            values: [core]
+          - variable: MODULE3
+            values: [files]
+          - variable: MODULE4
+            values: [storage]
+          - variable: NAME
+            values: [default_storage]
+      - variable: UNSANITIZED_DYNAMIC_INPUT
+        detection: python_django_path_traversal_dynamic_input
+        scope: result
+auxiliary:
+  - id: python_django_path_traversal_dynamic_input
+    sanitizer: python_django_path_traversal_sanitizer
+    patterns:
+      - pattern: $<UNSANITIZED_DYNAMIC_INPUT>
+        filters:
+          - variable: UNSANITIZED_DYNAMIC_INPUT
+            detection: python_shared_lang_dynamic_input
+            scope: cursor
+  - id: python_django_path_traversal_sanitizer
+    patterns:
+      - pattern: $<OS_PATH_NORMPATH>()
+        filters:
+          - variable: OS_PATH_NORMPATH
+            detection: python_shared_lang_import2
+            scope: result
+            filters:
+              - variable: MODULE1
+                values: [os]
+              - variable: MODULE2
+                values: [path]
+              - variable: NAME
+                values: [normpath]
+languages:
+  - python
+severity: high
+metadata:
+  description: Unsanitized dynamic input in file path
+  remediation_message: |
+    ## Description
+
+    Using unsanitized dynamic input to determine file paths can allow attackers to gain access to files and folders outside of the intended scope. This vulnerability occurs when input provided by users is directly used to access the filesystem without proper validation or sanitization.
+
+    ## Remediations
+
+    - **Do not** directly use external input to construct file paths. This can lead to unauthorized file access.
+    - **Do** sanitize external input used in file paths. Use `os.path.normpath` to normalize paths and remove any redundant separators in order to prevent path traversal attacks.
+      ```python
+      os.path.normpath(os.path.join(base_directory, user_input))
+      ```
+    - **Do** use absolute path checks to confirm that the constructed path is within the expected directory
+        ```python
+        base = os.path.abspath(base_directory)
+        user_path = os.path.abspath(os.path.join(base_directory, user_input))
+        if user_path.startswith(base)
+          # Handle or reject the input
+       ```
+
+    ## References
+
+    - [OWASP Path Traversal](https://owasp.org/www-community/attacks/Path_Traversal)
+  cwe_id:
+    - 22
+  id: python_django_path_traversal
+  documentation_url: https://docs.bearer.com/reference/rules/python_django_path_traversal

tests/python/django/path_traversal/test.js

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+const {
+  createNewInvoker,
+  getEnvironment,
+} = require("../../../helper.js")
+const { ruleId, ruleFile, testBase } = getEnvironment(__dirname)
+
+describe(ruleId, () => {
+  const invoke = createNewInvoker(ruleId, ruleFile, testBase)
+
+  test("path_traversal", () => {
+    const testCase = "main.py"
+
+    const results = invoke(testCase)
+
+    expect(results).toEqual({
+      Missing: [],
+      Extra: []
+    })
+  })
+})

tests/python/django/path_traversal/testdata/main.py

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+from django.core.files.storage import FileSystemStorage as FSS
+
+# bearer:expected python_django_path_traversal
+fs = FSS(sys.argv[0])
+request_file = request.FILES['document']
+file = fs.save(request_file)
+
+from django.core.files.storage import default_storage
+import os.path
+
+default_storage.save(os.path.normpath(sys.argv[1]))
+x = os.path.normpath(sys.argv[2])
+default_storage.save(x)