What are discretionary access control (DAC) and its limitations in terms of security risks?
Discretionary Access Control (DAC) is a security mechanism used in computer systems to regulate access to resources based on the identity and permissions of users. It allows the owner of a resource to determine who can access it and what actions can be performed on it. DAC is widely used in various operating systems, including Linux, to enforce security policies and protect sensitive data.
In DAC, each resource is associated with an access control list (ACL) that specifies the permissions granted to different users or groups. These permissions typically include read, write, and execute privileges. The owner of a resource can modify the ACL to grant or revoke permissions as needed. For example, in a Linux system, the chmod command can be used to change the permissions of a file or directory.
However, DAC has certain limitations that can pose security risks in computer systems. One limitation is the lack of granularity in access control. In DAC, permissions are typically assigned at the file or directory level, which means that all users with access to a particular resource have the same level of permissions. This can be problematic when different users require different levels of access to the same resource. For instance, in a shared directory, if one user needs read-only access while another user needs read-write access, DAC cannot enforce this level of granularity.
Another limitation of DAC is the reliance on the integrity of the owner of a resource. Since the owner has the ability to modify the ACL, there is a risk that the owner may accidentally or maliciously grant excessive permissions to unauthorized users. For example, if a user mistakenly changes the permissions of a sensitive file to allow public access, it can lead to unauthorized disclosure of sensitive information.
Additionally, DAC does not provide a centralized mechanism for managing access control policies. Each resource has its own ACL, making it difficult to enforce consistent access control across the entire system. This can result in inconsistencies or gaps in the security posture of the system. For instance, if an administrator forgets to set appropriate permissions on a newly created resource, it may inadvertently become accessible to unauthorized users.
Furthermore, DAC does not provide strong protection against insider threats. Since DAC relies on the identity of the user, it cannot prevent an authorized user from abusing their privileges to access or modify resources that they should not have access to. For example, a disgruntled employee with legitimate access to sensitive files can easily copy or modify them without being detected by DAC.
To mitigate these security risks, additional security mechanisms can be implemented in conjunction with DAC. For example, Role-Based Access Control (RBAC) can be used to provide a more fine-grained and centralized access control mechanism. RBAC allows access to resources based on the roles assigned to users, rather than their individual identities. This can help enforce consistent access control policies and reduce the risk of unauthorized access.
While DAC is a widely used access control mechanism in computer systems, it has limitations that can pose security risks. These limitations include the lack of granularity, reliance on the integrity of the owner, lack of centralized management, and vulnerability to insider threats. To address these limitations, additional security mechanisms such as RBAC can be implemented.
Other recent questions and answers regarding EITC/IS/CSSF Computer Systems Security Fundamentals:
- Is the goal of an enclave to deal with a compromised operating system, still providing security?
- Could machines being sold by vendor manufacturers pose a security threats at a higher level?
- What is a potential use case for enclaves, as demonstrated by the Signal messaging system?
- What are the steps involved in setting up a secure enclave, and how does the page GB machinery protect the monitor?
- What is the role of the page DB in the creation process of an enclave?
- How does the monitor ensure that it is not misled by the kernel in the implementation of secure enclaves?
- What is the role of the Chamorro enclave in the implementation of secure enclaves?
- What is the purpose of attestation in secure enclaves and how does it establish trust between the client and the enclave?
- How does the monitor ensure the security and integrity of the enclave during the boot-up process?
- What is the role of hardware support, such as ARM TrustZone, in implementing secure enclaves?
View more questions and answers in EITC/IS/CSSF Computer Systems Security Fundamentals