What is Access Control Entry?

Access Control Entry (ACE) is data within an access control list detailing the access privileges assigned to an individual user or a collective group of users. In the Access Control Entry system, an identification (ID) distinguishes each ACE and identifies the specific individual or group of subjects.


Each access control entry includes:

  • A security identifier (SID) representing a specific user or group
  • Bit flags that decide if child objects can inherit the ACE
  • A flag indicating the type of ACE
  • An access mask detailing permission rights


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Access Control List Types


An Access Control List (ACL) is similar to an organized list of rules that determine who can do what. ACLs contain many access control entries that define the access rights of different individuals or groups. Two varieties of ACLs exist:


Filesystem ACLs regulate access to files and directories, informing operating systems about user permissions and allowed actions.


Networking ACLs control access to the network, guiding routers and switches on permissible traffic types and activities.


Active Directory ACLs Microsoft’s Active Directory service operates as an LDAP server, storing and sharing setup details regarding users and computers within a domain. It enhances the LDAP specification by incorporating a similar access-control list mechanism found in the NTFS filesystem used by Windows NT. With Windows 2000, Microsoft expanded the syntax for access-control entries, enabling administrators to grant or deny access not only to entire LDAP objects but also to specific attributes within these objects.


ACLs traffic identification


ACLs can also categorize traffic identification:


Standard ACL

Standard ACLs, the original form of access control lists, filter network traffic by inspecting the source IP address in packets. To create a standard IP access list, you employ access-list numbers within the range of 1-99 or 1300-1999 (expanded range). These designated numbers inform the router that you intend to establish a standard IP access list, prompting the router to anticipate syntax that solely specifies the source IP address.


Extended ACL

Extended ACLs expand upon the capabilities of standard ACLs by considering both the source and destination addresses. They enable you to define the source and destination addresses, along with the protocol, TCP, and UDP port numbers that characterize them. Through extended access lists, you can grant users access to a physical LAN while preventing them from reaching particular hosts-or even specific services hosted on those systems.


Named ACL

Named ACL is a way to control network traffic flow by filtering packets based on specific criteria. It uses a meaningful name (e.g., “web_server_access”) making it easier to remember and associate with its purpose. This holds particular importance for documentation and ongoing maintenance tasks. Named ACL also configures entries within a dedicated mode, providing better organization.


Dynamic ACL

A dynamic ACL is an access control list whose entries are determined and applied during the execution of the access policy. These entries are stored and enforced for the duration of the access session. The ACL entries originate from a session variable, which can gather content from external sources like Active Directory, LDAP, RADIUS, or internal sources such as iRules, data groups, or a combination thereof.


Reflexive ACL

Reflexive ACL is commonly used in network security to control traffic flow based on dynamic session information.It dynamically tracks and permits return traffic for outbound connections initiated by devices within a network.They are commonly used in scenarios where traditional static ACLs may not be sufficient, such as in environments with dynamic IP addresses or for controlling traffic flows in stateful firewall configurations.


Context-based ACLs (CBACs)

These are ACLs that can be used to control access to resources based on the context of the request, such as the user’s identity, role, or location. CBACs can be used to implement more granular security policies.


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ACE Objects


There exist six types of ACEs, with three being supported by all securable objects, while the remaining three are Object-specific ACEs, upheld by directory service objects.


Object-specific ACEs are designed specifically for directory service (DS) objects. Within an object-specific ACE, a pair of GUIDs are included to broaden the scope of protection the ACE offers to an object.


This table lists the three types of Access Control Entries supported by all securable objects:

Type Description
Access-denied ACE Used in a discretionary access control list (DACL) to deny access rights to a trustee.
Access-allowed ACE Used in a DACL to allow access rights to a trustee.
System-audit ACE Used in a system access control list (SACL) to generate an audit record when the trustee attempts to exercise the specified access rights.


Discretionary Access Control List (DACL)

A discretionary access control list (DACL) specifies which users and groups have permission to access an object and which are denied access. If a user or group is not listed in the DACL, they will be denied access.

By default, the DACL is managed by the user who created the object or the owner of the object to which the DACL belongs. Similar to an ACL, each entry in the list is called an access control entry or ACE.


System Access Control List (SACL)


A SACL, or system access control list, is a list that tells the system which users or actions should be audited when they try to access an object. This helps in finding security issues and understanding the extent of damage.


Similar to a DACL, the owner or creator of the object usually controls SACLs by default. The access control entries (ACEs) in a SACL decide whether to record failed or successful attempts when a user tries to access the object.


ACE Vulnerabilities


There are many types of vulnerabilities relevant to ACEs such as:


Privilege Escalation: An attacker could exploit vulnerabilities in ACEs to gain unauthorized access to resources with higher privileges, potentially compromising the entire system.

Permission Bypass: Vulnerabilities could allow attackers to bypass intended access restrictions defined by ACEs, accessing and manipulating sensitive data without proper authorization.

Race Conditions: Certain vulnerabilities might arise from race conditions, where the order of operation between system processes creates unintended access paths due to misconfigured or flawed ACEs.

Logic Flaws: Errors in the logic used to evaluate ACEs could lead to unintended access grants or denials, potentially compromising system security.


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Access Control Entry Hardening


Hardening Access Control Entry (ACE) involves implementing measures to strengthen the security and resilience of access control mechanisms within an organization’s IT infrastructure. This process includes a thorough review and adjustment of access control lists (ACLs), ensuring only necessary permissions are granted, and following principles of least privilege and role-based access control (RBAC) to limit access based on users’ roles.


Regular monitoring, auditing, and updating of ACE configurations, alongside strong authentication methods and encryption, contribute to robust access control. Properly configuring ACEs involves adhering to the principle of least privilege, setting strict limits on resource permissions, and using precise ACE specifications. Automating the regular review of ACE settings for critical system components, alongside the application of advanced ACL configurations, further strengthens security and prevents privilege escalation.

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