pySCG: adding docs for CWE-1109 as part of #531

docs/Secure-Coding-Guide-for-Python/CWE-710/CWE-1109/README.md

@@ -0,0 +1,180 @@
+# CWE-1109: Use of Same Variable for Multiple Purposes
+
+Avoid reusing names of variables, functions, classes, built-in functions, packages, or standard Python modules
+
+Redefining identifiers from *The Python Standard Library* \[[Python 2025](https://docs.python.org/3/library/index.html)\], any internals `str` and `os` or other parts of the project can result in unexpected behavior and errors. Issues can multiply when identifiers are made global in a project.
+
+## Non-Compliant Code Example (Built-in Function)
+
+The redefined built-in function `len()` in `noncompliant01.py` in incorrectly adding each element to a "sum" instead of calculating the length of an object.
+
+*[noncompliant01.py](noncompliant01.py):*
+
+```python
+# SPDX-FileCopyrightText: OpenSSF project contributors
+# SPDX-License-Identifier: MIT
+"""Non-compliant Code Example"""
+
+number_list = [1, 2, 3, 4, 5, 6, 7, 8, 9]
+print(f"len({number_list}) == {len(number_list)}")
+
+
+def len(numbers: list[int]) -> int:
+    """implementing a dodgy version of a build in method"""
+    result = 0
+    for number in numbers:
+        result += number
+    return result
+
+
+#####################
+# Trying to exploit above code example
+#####################
+
+print(f"len({number_list}) == {len(number_list)}")
+
+```
+
+The first `print(f"len({number_list}) == {len(number_list)}")` using the original `len()` is listing the correct number of `9` entries.
+The second print statement using the redefined `len()` is listing `45`.  
+
+**Example output:**
+
+```bash
+len([1, 2, 3, 4, 5, 6, 7, 8, 9]) == 9
+len([1, 2, 3, 4, 5, 6, 7, 8, 9]) == 45
+```
+
+Redefining `len()` can break its usage for other data types such as strings causing crashes. The redefined `len()` will cause a `print(len("Hello World!"))` to throw a `TypeError` as we combine `int` with `char`.
+
+## Compliant Solution (Built-in Function)
+
+Ensure that all functions do not reuse the names as defined in Built-in Functions \[[Python built-in 2025](https://docs.python.org/3.9/library/functions.html)\] and do not reuse the identifiers as defined in The *The Python Standard Library* \[[Python 2025](https://docs.python.org/3/library/index.html)\].
+
+*[compliant01.py](compliant01.py):*
+
+```python
+# SPDX-FileCopyrightText: OpenSSF project contributors
+# SPDX-License-Identifier: MIT
+"""Compliant Code Example"""
+
+number_list = [1, 2, 3, 4, 5, 6, 7, 8, 9]
+print(f"len({number_list}) == {len(number_list)}")
+
+
+def custom_len(numbers: list[int]) -> int:
+    """implementing a dodgy version of a build in method"""
+    result = 0
+    for number in numbers:
+        result += number
+    return result
+
+
+#####################
+# Trying to exploit above code example
+#####################
+
+print(f"len({number_list}) == {len(number_list)}")
+
+```
+
+## Non-Compliant Code Example (Class)
+
+The standard module `os` and function `getpid()` are being redefined in `noncompliant02.py`.
+
+*[noncompliant02.py](noncompliant02.py):*
+
+```python
+# SPDX-FileCopyrightText: OpenSSF project contributors
+# SPDX-License-Identifier: MIT
+"""Non-compliant Code Example"""
+
+import os
+
+print(f"Process id='{os.getpid()}'")
+
+
+class os:
+    """redefining standard class"""
+
+    @staticmethod
+    def getpid():
+        """redefining standard class method"""
+        return "Not implemented"
+
+
+#####################
+# Trying to exploit above code example
+#####################
+
+print(f"Process id='{os.getpid()}'")
+
+```
+
+The `os.getpid()` method from the standard module is no longer called after redefining it and prints "Not implemented" instead of the process ID.
+
+**Example output:**
+
+```bash
+Process id='19354'
+Process id='Not implemented'
+```
+
+## Compliant Solution (Class)
+
+Ensure that all packages, classes and functions do not reuse the identifiers as defined in *The Python Standard Library* \[[Python 2025](https://docs.python.org/3/library/index.html)\].
+
+*[compliant02.py](compliant02.py):*
+
+```python
+# SPDX-FileCopyrightText: OpenSSF project contributors
+# SPDX-License-Identifier: MIT
+"""Compliant Code Example"""
+
+import os
+
+print(f"Process id='{os.getpid()}'")
+
+
+class custom_os:
+    """redefining standard class"""
+
+    @staticmethod
+    def getpid():
+        """redefining standard class method"""
+        return "Not implemented"
+
+
+#####################
+# Trying to exploit above code example
+#####################
+
+print(f"Process id='{os.getpid()}'")
+
+```
+
+## Automated Detection
+
+On the 'class' example we have `C0103` complains about missing PascalCase naming style, `R0801`: Similar lines in `2` files, and `R0903` we do not list as their detection is not in relation to the actual issue.
+
+|Tool|Version|Checker|Description|
+|:---|:---|:---|:---|
+|pylint|2.9.6|[W0622](https://pylint.pycqa.org/en/latest/user_guide/messages/warning/redefined-builtin.html?highlight=W0622)|Redefining built-in 'len' (redefined-builtin)|
+|pylint|2.9.6|[E0102](https://pylint.pycqa.org/en/latest/user_guide/messages/error/function-redefined.html)|class already defined line 5 (function-redefined), detecting `class os`:|
+
+## Related Guidelines
+
+|||
+|:---|:---|
+|[MITRE CWE](http://cwe.mitre.org/)|Pillar: [CWE-710: Improper Adherence to Coding Standards)](https://cwe.mitre.org/data/definitions/710.html)|
+|[MITRE CWE](http://cwe.mitre.org/)|Base: [CWE - CWE-1109: Use of Same Variable for Multiple Purposes](https://cwe.mitre.org/data/definitions/1109.html)|
+|[SEI CERT Coding Standard for Java](https://wiki.sei.cmu.edu/confluence/display/java/SEI+CERT+Oracle+Coding+Standard+for+Java)|[DCL01-J. Do not reuse public identifiers from the Java Standard Library](https://wiki.sei.cmu.edu/confluence/display/java/DCL01-J.+Do+not+reuse+public+identifiers+from+the+Java+Standard+Library)|
+|[SEI CERT C Coding Standard](https://web.archive.org/web/20220511061752/https://wiki.sei.cmu.edu/confluence/display/c/SEI+CERT+C+Coding+Standard)|[PRE04-C. Do not reuse a standard header file name](https://wiki.sei.cmu.edu/confluence/display/c/PRE04-C.+Do+not+reuse+a+standard+header+file+name)|
+|[SEI CERT C++ Coding Standard](https://wiki.sei.cmu.edu/confluence/pages/viewpage.action?pageId=88046682)|[VOID PRE04-CPP. Do not reuse a standard header file name](https://wiki.sei.cmu.edu/confluence/pages/viewpage.action?pageId=88046904)|
+
+## Bibliography
+
+|||
+|:---|:---|
+|\[Python 2025\].|*The Python Standard Library* \[online\]. Available from: <https://docs.python.org/3/library/index.html> \[accessed 24 June 2025\]|
+|\[Python built-in 2025\].|*Built-in Functions* \[online\]. Available from: <https://docs.python.org/3.9/library/functions.html> \[accessed 24 June 2025\]|

docs/Secure-Coding-Guide-for-Python/CWE-710/CWE-1109/compliant01.py

@@ -1,14 +1,21 @@
 # SPDX-FileCopyrightText: OpenSSF project contributors
 # SPDX-License-Identifier: MIT
-""" Compliant Code Example """
-numbers = ["one", "two", "three"]
+"""Compliant Code Example"""
 
-print(f"len({numbers}) == {len(numbers)}")
+number_list = [1, 2, 3, 4, 5, 6, 7, 8, 9]
+print(f"len({number_list}) == {len(number_list)}")
 
 
-def custom_len(x):
-    """ implementing a dodgy version of a build in method """
-    return sum(1 for _ in x) + 1
+def custom_len(numbers: list[int]) -> int:
+    """implementing a dodgy version of a build in method"""
+    result = 0
+    for number in numbers:
+        result += number
+    return result
 
 
-print(f"len({numbers}) == {len(numbers)}")
+#####################
+# Trying to exploit above code example
+#####################
+
+print(f"len({number_list}) == {len(number_list)}")

docs/Secure-Coding-Guide-for-Python/CWE-710/CWE-1109/compliant02.py

@@ -1,18 +1,23 @@
 # SPDX-FileCopyrightText: OpenSSF project contributors
 # SPDX-License-Identifier: MIT
-""" Compliant Code Example """
+"""Compliant Code Example"""
+
 import os
 
-print(f"Logged in user is {os.getlogin()}")
+print(f"Process id='{os.getpid()}'")
 
 
 class custom_os:
-    """ redefining standard class """
+    """redefining standard class"""
 
     @staticmethod
-    def getlogin():
-        """ redefining standard class method """
+    def getpid():
+        """redefining standard class method"""
         return "Not implemented"
 
 
-print(f"Logged in user is {os.getlogin()}")
+#####################
+# Trying to exploit above code example
+#####################
+
+print(f"Process id='{os.getpid()}'")

docs/Secure-Coding-Guide-for-Python/CWE-710/CWE-1109/noncompliant01.py

@@ -1,14 +1,21 @@
 # SPDX-FileCopyrightText: OpenSSF project contributors
 # SPDX-License-Identifier: MIT
-""" Non-compliant Code Example """
-numbers = ["one", "two", "three"]
+"""Non-compliant Code Example"""
 
-print(f"len({numbers}) == {len(numbers)}")
+number_list = [1, 2, 3, 4, 5, 6, 7, 8, 9]
+print(f"len({number_list}) == {len(number_list)}")
 
 
-def len(x):
-    """ implementing a dodgy version of a build in method """
-    return sum(1 for _ in x) + 1
+def len(numbers: list[int]) -> int:
+    """implementing a dodgy version of a build in method"""
+    result = 0
+    for number in numbers:
+        result += number
+    return result
 
 
-print(f"len({numbers}) == {len(numbers)}")
+#####################
+# Trying to exploit above code example
+#####################
+
+print(f"len({number_list}) == {len(number_list)}")

docs/Secure-Coding-Guide-for-Python/CWE-710/CWE-1109/noncompliant02.py

@@ -1,17 +1,23 @@
 # SPDX-FileCopyrightText: OpenSSF project contributors
 # SPDX-License-Identifier: MIT
-""" Non-compliant Code Example """
+"""Non-compliant Code Example"""
+
 import os
-print(f"Logged in user is {os.getlogin()}")
+
+print(f"Process id='{os.getpid()}'")
 
 
 class os:
-    """ redefining standard class """
+    """redefining standard class"""
 
     @staticmethod
-    def getlogin():
-        """ redefining standard class method """
+    def getpid():
+        """redefining standard class method"""
         return "Not implemented"
 
 
-print(f"Logged in user is {os.getlogin()}")
+#####################
+# Trying to exploit above code example
+#####################
+
+print(f"Process id='{os.getpid()}'")

docs/Secure-Coding-Guide-for-Python/readme.md

@@ -109,7 +109,7 @@ It is __not production code__ and requires code-style or python best practices t
 |[CWE-710: Improper Adherence to Coding Standards](https://cwe.mitre.org/data/definitions/710.html)|Prominent CVE|
 |:----------------------------------------------------------------|:----|
 |[CWE-1095: Loop Condition Value Update within the Loop](CWE-710/CWE-1095/README.md)||
-|[CWE-1109: Use of Same Variable for Multiple Purposes](CWE-710/CWE-1109/.)||
+|[CWE-1109: Use of Same Variable for Multiple Purposes](CWE-710/CWE-1109/README.md)||
 |[CWE-489: Active Debug Code](CWE-710/CWE-489/README.md)|[CVE-2018-14649](https://www.cvedetails.com/cve/CVE-2018-14649),<br/>CVSSv3.1: __9.8__,<br/>EPSS: __69.64__ (12.12.2023)|
 
 ## Biblography