COMP3371 Cyber Security

1. COMP3371 Cyber Security Richard Henson University of Worcester October2015

2. Week 5: Access Control using Active Directory • Objectives: • Explain the components of a network directory service • Analyse Windows active directory and compare it with an x500 standard service • Explain how the use of security policies can help prevent network internal security breaches • Apply security policies to a Windows Server setup

3. “Network Directories” & the PKI • Directories not to be confused with “folders”… • former is generally a data store that changes only infrequently… • e.g. a telephone directory • to avoid confusion, computer-based directories also called “repositories” • Lots of different “network databases” have evolved on the web • not a good idea! • often contain same info... one updated (e.g. someone’s address, all should be updated - but unlikely to be the case in practice

4. A Directory for the whole Internet? • Total solution: • use just one repository (meta directory) for that type of info (e.g. global telephone directory) • provide it on the web as a “directory service” • Use LDAP applications to directly access that info • Achieved through Distributed Directory…

5. Distributed Directory • Paper-based equivalent – series of telephone directories each covering a clearly define area • collectively cover a wide geographical region • serve a variety of purposes • all part of the same system for communication • Distributed directory on a computer network • Entry for an entity may appear in multiple directories • For example, one for each email system (if more than one) • For example, one for gaining access to the network by logging on • Directory synchronisation essential for tying the distributed directories together

6. Development of Internet Protocols: roles of IETF and IESG • IESG provides technical management of IETF activities • power to translate RFC proposals into RFC standards • Procedure: • draft RFC submitted • if accepted: IESG elevates it to RFC “draft” status • RFC then given consideration as a standard… • draft RFC eventually may become a true Internet standard • LDAP -> x509 good e.g. of successful evolution

7. X500 Architecture • Based on the OSI model • X500 agreed database spec: RFC 1006 • allows OSI applications to run over IP network • Full X500 Architecture: • DMD (directory management domain) • DUA (directory user agents) • DIB (directory information base – object oriented!) • e.g: a directory service database • DIT (directory information tree) • a hierarchical organization of entries which are distributed across one or more servers • DSA (directory system agent[s]) • works with DIT across servers

8. X500 Protocols • DAP (Directory Access protocol) • DSP (Directory System protocol) • DISP (Directory Information Shadowing Protocol) • DOP (Directory operational binding management protocol) • Collectively: • wide range of functionality • structure cumbersome

9. Simplifying X500 - LDAP • Developed by University of Michigan Researchers, early 1990s • gave up on the complexities of X.500 • came up with a scheme that: • retained the X.500 directory structure • gave it a streamlined access protocol based on standard TCP/IP instead of ISO • Other improvements: • pared-down referral mechanism • more flexible security model • no fixed replication protocol

10. Microsoft and LDAP • Microsoft wanted to get into the database server market, realised that Internet-compatibility was needed • needed X500 in its directory service planned for next version of NT • adapted Michigan Uni LDAP… • Microsoft helped build the original PKI service provider (Verisign) using the LDAP protocol • Also ODSI (Open Directory Services Interface): • allowed developers to build applications that register with, access, and manage multiple directory services with a single set of well-defined interfaces

11. Microsoft and x500 • 1996: launched Exchange v4 • email server • provided the infrastructure to enable DAP clients to access its directory service information… • Client-end X.500 DAP-compliant • Outlook as network client • Outlook Express as Internet client) • client for US gov defence messaging

12. Database for Exchange Server • Microsoft adopted/devised ESENT (Extensible Storage Engine… NT) database • arranged as a single file organised in a balanced B-tree hierarchical structure • Also used a new db engine ESE (JET blue) • uses ISAM (Indexed and Sequential Access) • manages data efficiently; crash recovery mechanism ensures data consistency is maintained even in the event of a system crash • in Windows as ESENT.DLL

13. X509 (Digital Certificates) • Digital Certificate store had to follow X500 standard to be “Internet compatible” • original X509 specification: RFC1422 (1993) • LDAP protocol for the “look up” • Refined many times… • current version RFC5280 (2008)

14. LDAP, ESE, and Active Directory • According to Microsoft… • “Active Directory incorporates decades of communication technologies into the overarching Active Directory concept…” • Certainly a very successful commercial roll out of an X500 compliant directory service • also used (uses) ESE to manage data • and DNS to integrate with www locations • and LDAP to manage PKI requests…

15. Continuous Development of AD • Continued to work with IETF • Exchange v5 also used the ESE/LDAP/DNS enhancement… • each version of Windows Server extended the Active Directory services further… • even Group Policies managed through AD • Development continues…

16. Directory Services and AD • Active Directory has just one data store, known as the directory • stored as NTFS.DIT • where does “.dit” originate from? • distributed across ALL thedomain controllers • links to objects on/controlled by each of the dc • changes automatically replicated to all dcs • Contains details of: • stored objects • shared resources • network user and computer accounts

17. AD, DNS, and Domain Trees • One great thing bout being Internet-compatible is that Active Directory can also logically link domains together • very useful for networksusing > one domain • each domain in the directory is identified by a DNS domain name and requires one or more domain controllers • Multiple domains with contiguous DNS domain names, make up a parent-child structure known as a domain tree • If Domain names are non-contiguous, they form separate domain trees

18. “Trust Relationships” between Windows Domains & using DNS • System of account authentication between domains was established in the Windows NT architecture • but Windows NT trust relationships were isolated and individual • Active Directory enables trust relationships through DNS naming • users and computers can be authenticated between any domains

19. Active Directory Trust Relationships • Extends the principle… • domains can link together in a schematic way • To form “domain trees” • Trust relationships are automatically created between adjacent domains (parent and child domains) in the tree • users and computers can now be authenticated between ANY domains in the domain tree • So how does this all work securely in practice, across an entire enterprise????

20. Access Controls • Set of security mechanisms used to control what a user can do as a result of logging on to a secured environment • enforce “authorisation” • “identification” and “authentication” may also be associated with logging on • Effect includes: • access to systems, services & resources • interactions users can perform

21. Remote Logon and Kerberos Authentication • Another university: MIT • Series of KDC (Kerberos Distribution Centres) • each a secure database of authorised users, passwords & domain names • maintained using Kerberos V5 security protocol • uses strong encryption • freely available… • Active Directory + Kerberos = Very Powerful combination • Even used to authenticate across mobile & wireless networks

22. Components of “Enterprise wide” Login with kerberos authentication • Active Directory tree logical connects and “trusts” servers throughout the enterprise • Servers in their turn control access to users within domains • Group(s) selected during the user authentication process • Group Policy Objects invoked which rewrite registry settings and control client desktops

23. Users, Groups, Security, and NTFS partitions • Any file or folder on an NTFS partition will have file permissions imposed • Typical permissions: • No Access • Read only • Read and Execute • Write • Modify • Ownership/Full Control • Much wider range of permissions available

24. Point for debate: is “read only” access dangerous? • If information held on server, and accessed by dumb terminals… • secure enough! • this was the case in the days of centralised networks with no distributed processing • With client-server networking, read only means “the user can take a copy” • is this dangerous, from an organisational security point of view?

25. Principle of Least Privilege • Providing users with sufficient access to do their work… • but no more than that! • Privileges can also be applied temporarily to provide controlled flexibility • Even individual administrators can have the principle applied to them • if they have responsibility for particular resources… • shouldn’t have privileges relating to other resources not within their work remit

26. Groups and Group Policy • May be convenient for managers and administrators to put users into groups • Settings for group provides particular access to data & services • Problems… • user in wrong group(s) • group has wrong settings

27. The Registry and User Control • The Registry - a simple data store • has many user settings • Settings uploaded into memory on boot-up • easily overwritten by settings from policy files • policies can be used for groups of users • resultant policy controls the desktop

28. What is The Registry? • A hierarchical and “active” store of system and user settings viewable using REGEDT32.exe • Five basic subtrees: • HKEY_LOCAL_MACHINE : local computer info. Does not change no matter which user is logged on • HKEY_USERS : default user settings • HKEY_CURRENT_USER : current user settings • HKEY_CLASSES_ROOT : software config data • HKEY_CURRENT_CONFIG : “active” hardware profile • Each subtree contains one or more subkeys

29. Location of the Windows Registry • c:\windows\system32\config • “users” may be denied access • Six files (no extensions): • Software • System – hardware settings • Sam, Security • not viewable through regedt32 • Default – default user • Sysdiff – HKEY USERS subkeys • Also: ntuser.dat file • user settings that override default user

30. Structure of anActive Directory Tree • A hierarchical system of organisational data objects • A Tree can be • single domain with org. units • group of domains

31. Domain, Trees & Forests • Domain objects divide into organisational units (OUs) • Microsoft recommend using OUs in preference to domains for imposing structure for admin purposes • flexibility to use either one domain or several… • “Forest” contains data needed to connect all objects in the tree even connect different trees • Logical linking creates “trusts” for remote users

32. Active Directory and DNS • DNS (Domain Name System) • Internet-based system for naming host computers • In Active Directory • each server in the tree has a unique IP address • but only domains can have a unique DNS identity • potential confusion when setting up domain structure!!

33. Managing Security Across a Directory Tree • Different admin levels: • domain admin: look after domain • enterprise admin: control all domains in the organisation! • justification of those large salaries? • Achieved through Group Policies… • users with different needs • but they had better be right!

34. Group Policy in Windows Networks • Group Policy settings define the various components of the user's desktop environment that a system administrator needs to manage: • programs that are available to users • programs that appear on the user's desktop • Start menu options • Group Policy Objects – used with authenticated users to enhance flexibility and scalability of security beyond “domains”, and “trusted domains” • Required level of trust achieved through: • Active directory “trees” based on DNS • Kerberos authentication

35. Implementation of Group Policy Objects • Group Policy Objects (GPO) are EXTREMELY POWERFUL… • contain all specified settings to give a group of users their desktop with agreed security levels applied • template editing tool available as a “snap-in” with Windows Servers • Policy provides a specific desktop configuration for a particular group of users • The GPO is in turn associated with selected Active Directory objects: • Sites, Domains, organizational units

36. Combined Power of Group Policies and Active Directory • Enables written user/group policies to be easily implemented in software • Enables policies to be applied across whole domains: • beyond in trusted contiguous domains in the domain tree • Or, using kerberos, even across any non-contiguous domains in the same forest