GitHub Security Advisory: GHSA-3x2w-63fp-3qvw
Package: scitokens (PIP)
Severity: HIGH (CVSS 8.1)
CWE: CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Vulnerable versions: < 1.9.7
Patched in: 1.9.7

Summary: SciTokens has an Authorization Bypass via Path Traversal in Scope Validation

Details:
### Summary
The `Enforcer` is vulnerable to a path traversal attack where an attacker can use dot-dot (`..`) in the `scope` claim of a token to escape the intended directory restriction. This occurs because the library normalizes both the authorized path (from the token) and the requested path (from the application) before comparing them using `startswith`.

### Details
**File:** `src/scitokens/scitokens.py`  
**Methods:** `_check_scope`, `_scope_path_matches`  
**File:** `src/scitokens/urltools.py`  
**Method:** `normalize_path`

## Description
When a token is verified, the `Enforcer` extracts the authorized path from the `scope` or `scp` claim. This path is passed through `urltools.normalize_path`, which uses `posixpath.normpath` to resolve relative segments.

If a token has a scope like `read:/home/user1/..`, the normalization process converts this to `/home`. When the enforcer checks if a request for `/home/user2` is authorized, it compares it against the normalized path `/home`.

### Vulnerable Logic Flow:

1.  **Normalization:** In `_check_scope`, the path `/home/user1/..` is normalized to `/home`.
2.  **Comparison:** In `_scope_path_matches`, the requested path `/home/user2` is checked against the allowed path `/home`:
    ```python
    return requested_path.startswith(allowed_path + '/')
    # "/home/user2".startswith("/home/") is True
    ```

### Bypassing with URL Encoding:
Since `normalize_path` unquotes the path before normalizing, an attacker can also use URL-encoded dots (e.g., `%2e%2e`) to hide the traversal from simple string filters that don't account for encoding.

### Root Traversal:
A scope like `read:/anything/..` normalizes to `read:/`, which grants access to the entire file system (or whatever resource space the enforcer is guarding).

## Impact
An attacker who can influence the `scope` claim (e.g., in environments where tokens are issued with user-provided sub-paths) can gain access to directories and files outside of their intended authorization.

## Proof of Concept
The following examples demonstrate the bypass (see `poc_path_traversal.py` for a full reproduction):

- **Scope:** `read:/home/user1/..` -> **Access Granted to:** `/home/user2`
- **Scope:** `read:/anything/..` -> **Access Granted to:** `/etc/passwd`
- **Scope:** `read:/foo/%2e%2e/bar` -> **Access Granted to:** `/bar`
```


import scitokens
import os
import sys

# Ensure we can import from src
if os.path.exists("src"):
    sys.path.append("src")

def test_path_traversal_bypass():
    print("--- Proof of Concept: Path Traversal in Scope Validation ---")
    
    issuer = "https://scitokens.org"
    enforcer = scitokens.Enforcer(issuer)
    
    # Imagine an application that expects to restrict a user to their own directory: /home/user1
    # The application validates that the token has 'read' access to /home/user1
    
    # MALICIOUS TOKEN
    # An attacker provides a token with a scope that uses '..' to traverse up.
    # 'read:/home/user1/..' effectively re