CWE-842: Placement of User into Incorrect Group

What is Placement of User into Incorrect Group?

• Overview: Placement of User into Incorrect Group (CWE-842) occurs when a user is mistakenly assigned to a group with inappropriate access levels, potentially granting them unintended privileges and access to sensitive resources.

• Exploitation Methods:

• Attackers can exploit this vulnerability by gaining unauthorized access through the improperly assigned group privileges.
• Common attack patterns include privilege escalation and lateral movement within a system to access restricted data or execute unauthorized actions.

• Security Impact:

• Direct consequences include unauthorized access to sensitive data and resources.
• Potential cascading effects involve the compromise of additional accounts or systems due to elevated privileges.
• Business impact can include data breaches, loss of customer trust, regulatory penalties, and financial loss.

• Prevention Guidelines:

• Specific code-level fixes include implementing strict group membership validation and review processes.
• Security best practices involve conducting regular audits of group memberships and access levels.
• Recommended tools and frameworks include using centralized identity and access management (IAM) solutions to automate and monitor group assignments.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

def assign_group(user_id, requested_group):
    # Simulate a user database and group assignment
    user_db = {
        1: {'username': 'alice', 'groups': ['user']},
        2: {'username': 'bob', 'groups': ['user']}
    }

    # Directly trusting the requested_group parameter without validation
    user_db[user_id]['groups'].append(requested_group)  # Vulnerability: No validation of requested_group

    return user_db[user_id]['groups']

# Usage
print(assign_group(1, 'admin'))  # User 'alice' is incorrectly placed into the 'admin' group

Vulnerability Explanation

The code above demonstrates a vulnerability where a user can be placed into an incorrect group due to lack of validation. By directly appending the requested_group parameter to the user's groups, any group name can be added, including privileged groups like 'admin'. This could allow unauthorized users to escalate privileges.

How to fix Placement of User into Incorrect Group?

To fix this vulnerability, we need to implement a validation mechanism that ensures only authorized group assignments are made. This involves:

1. Defining a set of permissible group assignments: Only allow specific users to be assigned to specific groups.
2. Implementing checks and balances: Use validation logic to confirm that the user requesting the group change has the authority to do so.
3. Logging and auditing: Keep logs of group assignment changes for auditing purposes.

Fixed Code Example

def assign_group(user_id, requested_group, actor_id):
    # Simulate a user database and group assignment
    user_db = {
        1: {'username': 'alice', 'groups': ['user']},
        2: {'username': 'bob', 'groups': ['user']}
    }

    # Define valid group assignments for each user
    valid_group_assignments = {
        1: ['user', 'editor'],  # Alice can only be 'user' or 'editor'
        2: ['user']  # Bob can only be 'user'
    }

    # Check if the requested group is valid for the user and if the requester has the authority
    if requested_group in valid_group_assignments.get(user_id, []) and actor_id == 1:  # Assume actor_id 1 is an admin
        user_db[user_id]['groups'].append(requested_group)
    else:
        raise PermissionError("Invalid group assignment or insufficient permissions")

    return user_db[user_id]['groups']

# Usage
try:
    print(assign_group(1, 'editor', 1))  # Valid change by authorized user
except PermissionError as e:
    print(e)

try:
    print(assign_group(1, 'admin', 1))  # Invalid change, 'admin' is not allowed
except PermissionError as e:
    print(e)

Fix Explanation

• Validation of Group Assignments: We introduced a valid_group_assignments dictionary to explicitly define which groups each user can be part of. This prevents arbitrary group assignments by restricting them to predefined values.
• Authorization Check: Added an actor_id parameter to ensure that the entity requesting the change has the authority to do so. In this example, only the user with actor_id 1 (assumed to be an administrator) can perform group assignments.
• Error Handling: Introduced error handling to raise a PermissionError if an invalid group assignment is attempted, providing feedback to the calling function.
• Logging and Auditing: While not shown in the code, implementing logging of all group changes can provide an audit trail for further security analysis and accountability.

The improved examples now adhere to best practices for Python, with proper syntax highlighting and clear explanations of both the vulnerability and the fix.