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Cybersecurity > Chapter 4 - Access Control > Flashcards

Chapter 4 - Access Control Flashcards

1
Q

Acess Control Definition

Define Access Control

A

The prevention of unauthorized access of a resource (or entering into physical facility)

also prevent legitimate users from using in unauthorize way

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2
Q

RFC Definition (of computer security)

Define Access Control

A

Process by which use of system** resources** is regulated according to a security policy and permitted only by authorized entities

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3
Q

Difference between User Authentication and Access Control

Define Access Control

A

Authentication establishes **who **you are and Access control establishes what you can do within a system

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4
Q

Relationship to other security functions

Define Access Control

“Broader Context of Access Control”

A
  1. Authentication: first verifies credentials of user are valid
  2. Access Control: Grants permissions to a system resource
  3. Auditing: Independent review of system records and activities to test adequacy, ensure compliance, and detect breaches
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5
Q

Access control policies should dictate:

Access Control Principles

A
  • Who can access a resource
  • What type of access is allowed
  • Under what conditions
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6
Q

Access Control Basic Elements

Access Control Basic Elements

A
  1. Subject (entity capable of accessing objects)
  2. Object (Resource to be accessed)
  3. Access Rights (What subject can do with object)

Subjects held accountable for actions they initiate!!!

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7
Q

Classes of Subject (3)

Access Control Basic Elements

A
  1. Owner
  2. Group
  3. World
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8
Q

Examples of Access Rights

Access Control Basic Elements

A
  • read
  • write
  • execute
  • delete
  • create
  • search
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9
Q

What are the three main Access Control Policies?

Access Control Principles

A
  1. Discretionary Access Control (DAC): Based on identity of requestor
  2. Mandatory Access Control (MAC): Based on labels and security clearances
  3. Role-based Access Control (RBAC): Based on roles that users have in system

Not mutually exclusive, we can implement multiple at once!!!

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10
Q

DAC definition

DAC

A

Scheme in which an entity may enable another entity to access some resource

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11
Q

How is DAC often implemented?

DAC

A

An access matrix where:

  • Rows = subjects
  • Columns = objects
  • Each cell = access rights

(That subject has to an object)

The value of cell password file:Eric = read

*From these we make access control lists and capability lists

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12
Q

Why use ACLs or Capability Lists?

DAC

A
  • Access matrix can become huge
  • most of the cells are empty which wastes space
  • changing permissions requires modifying matrix, more cumbersome than list
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13
Q

What are Access Control Lists (ACLs)

DAC

A

List of subjects that can acccess a particular object

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14
Q

What are capability lists?

DAC

A

List of objects that a particular subject can access

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15
Q

ACL
Pro vs Con

DAC

A

Pro:
* Object owner can easily control who can access their resource

Con:
* Takes up too much space/search overhead (Many more objects in system compared to subjects)

good for managing permissions from perspective of objects (unix)

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16
Q

Capability List
Pro vs Con

DAC

A

Pro:
* Easy to see what a user is allowed to access
* More flexible, subjects can access many objects and its easier to control that with capability lists

Con:
* Harder to manage by object (see all subjects that can access specific object)

Good for user-focused resource control

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17
Q

How are UNIX files managed?

DAC

A

inodes

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18
Q

What is an inode (index node) in Unix

DAC

A

A data structure in Unix that stores key information about a file for operating systemsto provide efficient hierarchical organization and access control

Does not contain file name or file contents

  • File Attributes
  • File permissions
  • File control information

remember directory = file with list of file names and their respective inodes

19
Q

inode table

A

stored in disk, contains inodes of all files in filesystem

20
Q

What happens when a Unix file is opened

DAC

A

Its inode is brought into main memory (in memory-resistant inode table)

Inode table contains inodes of all files in the file system

  1. System checks:
    * UID (unique user ID)
    * GID (Group ID)
    * Protection bits (Specify access permissions)
  2. System grants either owner (UID), group (GID) or other class permissions
21
Q

How are the 12 protection bits used to show permissions?

DAC

A

Here’s a clearer version you can update your flashcard with:

Q: How are the 12 protection bits used to show permissions?
A:
1. 3 bits – Owner (rwx)
2. 3 bits – Group (rwx)
3. 3 bits – Other (rwx)
4. 3 bits – Special permissions:

•	SUID (Set User ID):
•	s – Execute bit is set (rwsr-xr-x)
•	S – Execute bit is not set (rwSrw-r--)
•	SGID (Set Group ID):
•	s – Execute bit is set (rwxr-sr-x)
•	S – Execute bit is not set (rwxrwS--)
•	Sticky Bit:
•	t – Execute bit is set (rwxr-xr-t)
•	T – Execute bit is not set (rwxr-xr-T)

Special bits explanation:
• Lowercase (s or t) – Execute permission is present.
• Uppercase (S or T) – Execute permission is not present, but the special permission still applies

22
Q

what happens when stickybit is applied to directory

A

only owners of files in directory can rename, move or delete users

23
Q

What does this 12 bit permission structure imply?

rwxr-x—

DAC

A
  1. Owner can read, write and execute (all permissions)
  2. Group can read and execute but not write
  3. Other classes have no permission
  4. No special permissions
24
Q

What does this 12 bit permission structure imply?

rwxr-sr–T

DAC

A
  1. Owner can read, write, and execute
  2. Group can read and execute with owner permissions
  3. Others can only read
  4. Only owner can delete/rename files
25
Q

rwxr–r–T

A
  • Owner can read, write, and execute.
  • Group can read.
  • Others can read.
  • Only the owner can delete the file.

because stickybit is located in execute field of other, we use t or T to decide if other can execute or not. T MEANS THEY CAN’T

26
Q

rwsr-sr– how is this 12 bits?

A

111 110 100 001

The 9-character representation does not grow beyond 9 characters. It overlays the 12 bits by modifying the x positions for special permissions.

27
Q

Set UserID (SUID)
and
Set Group ID (SGID)

DAC

A
  • or SUID means file will be executed w/ same permissions as owner of executable file
  • GUID means executed with same permissions as group owner of the file

Ex: Passwd comman needs to edit files like /etc/passwd to change password, but these files are owned by root and can only be modified by root.

28
Q

Why should you be careful with special permissions like SUID and SGID?

DAC

A

Attackers can inject malicious commands as root user

29
Q

Role of superuser (root) in Unix

DAC

A

Exempt from usual access restrictions

Has system-wide access

Can install software and manage users

Kernel can only run with superuser privileges

NEVER run untrusted software with superuser

30
Q

Why is the traditional Unix file access control inadequate for complex environments?

DAC

A

No individual user control, would require huge number of groups, impossible to represent some constraints

Modern Unix systems like Linux and FreeBSD support ACLs

31
Q

What do Modern UNIX systems support instead of the traditional file access control?

DAC

A

ACLs

More fine-grained control than traditional 12-bit protection system

  • setfacl: Used to assign an ACL to a file or directory.
  • getfacl: Used to retrieve and display the ACL associated with a file or directory.
32
Q

Why is ACL Model better than traditional 12-bit permission system?

DAC

A

Extends these permissions: more granular assignments.

Traditional Permissions:
You would either need to add them all to the group or open access to “others.”
ACLs:
Assign specific read, write, or execute permissions to only the required users, without affecting the rest of the group or “others.”

33
Q

What is an Access Control List (ACL) in Unix

DAC

A

ACL tailored to Unix or Unix-like systems to extend the traditional permission model (owner, group, others), to allow defining permissions for individual users (beyond owner, group, others)

• still maintaining hierarchical structure
• Set mask for added control

34
Q

What is the two-step process in ACL model in UNIX?

DAC

A

Process requests access to file:
1. OS selects most appropriate ACL entry (Owner, user, group, or others)
2. OS verifies if the matching entry grants sufficient permissions to fulfill the request

35
Q

Mask in ACL model

DAC

A

Sets maximum permissions for group/named entries, even if some are assigned higher permissions

36
Q

What is Mandatory Access Control (MAC)?

MAC

A

Access is determined by system-enforced security labels and classifications, often used in military settings

Labeling mechanism used

Prevent illegal flow of information through the enforcement of “multi-level security”

37
Q

Downside of MAC

MAC

A

Requires a very strict classification of subject and objects, making it too rigid

Information access limited by the “need-to-know

38
Q

Compartment

MAC

A

Projects that are associated with a piece of classified information

Maybe file is labeled Secret;Finance – Secret Clearance and Finance Compartment access

39
Q

Classification
vs
Clearance

MAC

A

Classification: Class of an object
Clearance: Indication that a subject is trusted up to a certain level

“A subject can read an object is the subject dominates the object”

40
Q

What is a “Need-to-Know” Principle in MAC?

A

Access is limited to users who require it for their duties, even if they have the proper security clearance

41
Q

Role-Based Access Control (RBAC)

RBAC

A

Access is granted based on roles assigned to users, rather than user identities

  • Users assigned to different roles
  • widespread commercial use and area of active research, NIST standards developed
42
Q

What is RBAC0?

RBAC0

A

Base model in 4 model RBAC family (basis for RBAC standardization efforts, as they are actually ongoing) Containing four types of entities
1. User (individual accessing system)
2. Role (named job function)
3. Permission (approval of particular mode of access to one or more objects)
4. Session (mapping between a user and an activated subset of their roles)

43
Q

What is RBAC2?

RBAC2

A
  1. Mutually Exclusive Roles (only user can assume one role from a set)
  2. Cardinality: Limits on the number of users per role
  3. Prerequisite Roles: Users must have a specific role before assuming another
44
Q

What is RBAC1?

RBAC1

A

It adds role hierarchies to the basic RBAC model, where roles inherit permissions from subordinate roles.

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