NewSID

            Copyright © 1997-2002  Mark Russinovich and Bryce Cogswell

                               Last updated December 9, 2002 v4.0 


                               Introduction
                               Many organizations use disk image cloning to 
                              perform mass rollouts of Windows. This technique 
                              involves copying the disks of a fully installed 
                              and configured Windows computer onto the disk 
                              drives of other computers. These other computers 
                              effectively appear to have been through the same 
                              install process, and are immediately available for 
                              use. 

                              While this method saves hours of work and hassle 
                              over other rollout approaches, it has the major 
                              problem that every cloned system has an identical 
                              Computer Security Identifier (SID). This fact 
                              compromises security in Workgroup environments, 
                              and removable media security can also be 
                              compromised in networks with multiple identical 
                              computer SIDs.

                              Demand from the Windows community has lead 
                              PowerQuest, Ghost Software and Altiris to develop 
                              programs that can change a computer's SID after a 
                              system has been cloned. However, PowerQuest's SID 
                              Changer and Ghost Software's Ghost Walker are only 
                              sold as part of each company's high-end product. 
                              Further, they both run from a DOS command prompt 
                              (Altiris' changer is similar to NewSID).

                              NewSID is a program we developed that changes a 
                              computer's SID. It is free, comes with full 
                              source, and is a Win32 program, meaning that it 
                              can easily be run on systems that have been 
                              previously cloned. NewSID works Windows NT 4, 
                              Windows 2000, Windows XP and Windows .NET Server. 
                              Please read this entire article before you use 
                              this program.

                              Version Information: 
                                Version 4.0 introduces support for Windows XP 
                                and .NET Server, a wizard-style interface, 
                                allows you to specify the SID that you want 
                                applied, and also the option to rename a 
                                computer (which results in a change of both 
                                NetBIOS and DNS names). 
                                Version 3.02 corrects a bug where NewSid would 
                                not correctly copy default values with invalid 
                                value types when renaming a key with an old SID 
                                to a new SID. NT actually makes use of such 
                                invalid values at certain times in the SAM. The 
                                symptom of this bug was error messages reporting 
                                access denied when account information was 
                                updated by an authorized user. 
                                Version 3.01 adds a work-around for an 
                                inaccessible Registry key that is created by 
                                Microsoft Transaction Server. Without the 
                                work-around NewSID would quit prematurely. 
                                Version 3.0 introduces a SID-sync feature that 
                                directs NewSID to obtain a SID to apply from 
                                another computer. 
                                Version 2.0 has an automated-mode option, and 
                                let's you change the computer name as well. 
                                Version 1.2 fixes a bug in that was introduced 
                                in 1.1 where some file system security 
                                descriptors were not updated. 
                                Version 1.1 corrects a relatively minor bug that 
                                affected only certain installations. It also has 
                                been updated to change SIDs associated with the 
                                permission settings of file and printer shares. 

                               Cloning and Alternate Rollout Methods
                               One of the most popular ways of performing mass 
                              Windows rollouts (typically hundreds of computers) 
                              in corporate environments is based on the 
                              technique of disk cloning. A system administrator 
                              installs the base operating system and add-on 
                              software used in the company on a template 
                              computer. After configuring the machine for 
                              operation in the company network, automated disk 
                              or system duplication tools (such as Ghost 
                              Software's Ghost, PowerQuest's Image Drive, 
                              Altiris' RapiDeploy, and Innovative Software's 
                              ImageCast) are used to copy the template 
                              computer's drives onto tens or hundreds of 
                              computers. These clones are then given final 
                              tweaks, such as the assignment of unique names, 
                              and then used by company employees.

                              Another popular way of rolling out is by using the 
                              Microsoft sysdiff utility (part of the Windows 
                              Resource Kit). This tool requires that the system 
                              administrator perform a full install (usually a 
                              scripted unattended installation) on each 
                              computer, and then sysdiff automates the 
                              application of add-on software install images. 

                              Because the installation is skipped, and because 
                              disk sector copying is more efficient than file 
                              copying, a cloned-based rollout can save dozens of 
                              hours over a comparable sysdiff install. In 
                              addition, the system administrator does not have 
                              to learn how to use unattended install or sysdiff, 
                              or create and debug install scripts. This alone 
                              saves hours of work.
                               The SID Duplication Problem
                               The problem with cloning is that it is only 
                              supported by Microsoft in a very limited sense. 
                              Microsoft has stated that cloning systems is only 
                              supported if it is done before the GUI portion of 
                              Windows Setup has been reached. When the install 
                              reaches this point the computer is assigned a name 
                              and a unique computer SID. If a system is cloned 
                              after this step the cloned machines will all have 
                              identical computer SIDs. Note that just changing 
                              the computer name or adding the computer to a 
                              different domain does not change the computer SID. 
                              Changing the name or domain only changes the 
                              domain SID if the computer was previously 
                              associated with a domain.

                              To understand the problem that cloning can cause, 
                              it is first necessary to understand how individual 
                              local accounts on a computer are assigned SIDs. 
                              The SIDs of local accounts consist of the 
                              computer's SID and an appended RID (Relative 
                              Identifier). The RID starts at a fixed value, and 
                              is increased by one for each account created. This 
                              means that the second account on one computer, for 
                              example, will be given the same RID as the second 
                              account on a clone. The result is that both 
                              accounts have the same SID.

                              Duplicate SIDs aren't an issue in a Domain-based 
                              environment since domain accounts have SID's based 
                              on the Domain SID. But, according to Microsoft 
                              Knowledge Base article Q162001, "Do Not Disk 
                              Duplicate Installed Versions of Windows NT", in a 
                              Workgroup environment security is based on local 
                              account SIDs. Thus, if two computers have users 
                              with the same SID, the Workgroup will not be able 
                              to distinguish between the users. All resources, 
                              including files and Registry keys, that one user 
                              has access to, the other will as well.

                              Another instance where duplicate SIDs can cause 
                              problems is where there is removable media 
                              formated with NTFS, and local account security 
                              attributes are applied to files and directories. 
                              If such a media is moved to a different computer 
                              that has the same SID, then local accounts that 
                              otherwise would not be able to access the files 
                              might be able to if their account IDs happened to 
                              match those in the security attributes. This is 
                              not be possible if computers have different SIDs.

                              An article Mark has written, entitled "NT Rollout 
                              Options", was published in the June issue of 
                              Windows NT Magazine. It discusses the duplicate 
                              SID issue in more detail, and presents Microsoft's 
                              official stance on cloning. To see if you have a 
                              duplicate SID issue on your network, use PsGetSid 
                              to display machine SIDs.
                               NewSID
                               NewSID is a program we developed to change a 
                              computer's SID. It first generates a random SID 
                              for the computer, and proceeds to update instances 
                              of the existing computer SID it finds in the 
                              Registry and in file security descriptors, 
                              replacing occurrences with the new SID. NewSID 
                              requires administrative privileges to run. It has 
                              two functions: changing the SID, and changing the 
                              computer name. 

                              To use NewSID's auto-run option, specify "/a" on 
                              the command line. You can also direct it to 
                              automatically change the computer's name by 
                              including the new name after the "/a" switch. For 
                              example:

                                     newsid /a [newname]

                              Would have NewSID run without prompting, change 
                              the computer name to "newname" and have it reboot 
                              the computer if everything goes okay.

                              NewSID's SID-synchronizing feature that allows you 
                              to specify that, instead of randomly generating 
                              one, the new SID should be obtained from a 
                              different computer. This functionality makes it 
                              possible to move a Backup Domain Controller (BDC) 
                              to a new Domain, since a BDC's relationship to a 
                              Domain is identified by it having the same 
                              computer SID as the other Domain Controllers 
                              (DCs). Simply choose the "Synchronize SID" button 
                              and enter the target computer's name. You must 
                              have permissions to change the security settings 
                              of the target computer's Registry keys, which 
                              typically means that you must be logged in as a 
                              domain administrator to use this feature.

                              Note that when you run NewSID that the size of the 
                              Registry will grow, so make sure that the maximum 
                              Registry size will accomodate growth. We have 
                              found that this growth has no perceptible impact 
                              on system performace. The reason the Registry 
                              grows is that it becomes fragmented as temporary 
                              security settings are applied by NewSID. When the 
                              settings are removed the Registry is not 
compacted.

                              Note that while we have thoroughly tested NewSID, 
                              you must use it at your own risk. As with any 
                              software that changes file and Registry settings, 
                              it is highly recommended that you completely 
                              back-up your computer before running NewSID.
                               Moving a BDC
                               Here are the steps you should follow when you 
                              want to move a BDC from one domain to another: 
                                Boot up the BDC you want to move and log in. Use 
                                NewSID to synchronize the SID of the BDC with 
                                the PDC of the domain to which you wish to move 
                                the BDC. 
                                Reboot the system for which you changed the SID 
                                (the BDC). Since the domain the BDC is now 
                                associated with already has an active PDC, it 
                                will boot as a BDC in its new domain. 
                                The BDC will show up as a workstation in Server 
                                Manager, so use the "Add to Domain" button to 
                                add the BDC to its new domain. Be sure to 
                                specify the BDC radio button when adding. 

                               How it Works
                               NewSID starts by reading the existing computer 
                              SID. A computer's SID is stored in the Registry's 
                              SECURITY hive under SECURITY\SAM\Domains\Account. 
                              This key has a value named F and a value named V. 
                              The V value is a binary value that has the 
                              computer SID embedded within it at the end of its 
                              data. NewSID ensures that this SID is in a 
                              standard format (3 32-bit subauthorities preceded 
                              by three 32-bit authority fields).

                              Next, NewSID generates a new random SID for the 
                              computer. NewSID's generation takes great pains to 
                              create a truly random 96-bit value, which replaces 
                              the 96-bits of the 3 subauthority values that make 
                              up a computer SID.

                              Three phases to the computer SID replacement 
                              follow. In the first phase, the SECURITY and SAM 
                              Registry hives are scanned for occurrences of the 
                              old computer SID in key values, as well as the 
                              names of the keys. When the SID is found in a 
                              value it is replaced with the new computer SID, 
                              and when the SID is found in a name, the key and 
                              its subkeys are copied to a new subkey that has 
                              the same name except with the new SID replacing 
                              the old. 

                              The final two phases involve updating security 
                              descriptors. Registry keys and NTFS files have 
                              security associated with them. Security 
                              descriptors consist of an entry that identifies 
                              which account owns the resource, which group is 
                              the primary group owner, an optional list of 
                              entries that specify actions permitted by users or 
                              groups (known as the Discretionary Access Control 
                              List - DACL), and an optional list of entries that 
                              specify which actions performed by certain users 
                              or groups will generate entries in the system 
                              Event Log (System Access Control List - SACL). A 
                              user or a group is identified in these security 
                              descriptors with their SIDs, and as I stated 
                              earlier, local user accounts (other than the 
                              built-in accounts such as Administrator, Guest, 
                              and so on) have their SIDs made up of the computer 
                              SID plus a RID.

                              The first part of security descriptor updates 
                              occurs on all NTFS file system files on the 
                              computer. Every security descriptor is scanned for 
                              occurrences of the computer SID. When NewSID finds 
                              one, it replaces it with the new computer SID.

                              The second part of security descriptor updates is 
                              performed on the Registry. First, NewSID must make 
                              sure that it scans all hives, not just those that 
                              are loaded. Every user account has a Registry hive 
                              that is loaded as HKEY_CURRENT_USER when the user 
                              is logged in, but remains on disk in the user's 
                              profile directory when they are not. NewSID 
                              identifies the locations of all user hive 
                              locations by enumerating the 
                              HKEY_LOCAL_MACHINE\Software\Microsoft\Windows 
                              NT\CurrentVersion\ProfileList key, which points at 
                              the directories in which they are stored. It then 
                              loads them into the Registry using RegLoadKey 
                              under HKEY_LOCAL_MACHINE and scans the entire 
                              Registry, examining each security descriptor in 
                              search of the old computer SID. Updates are 
                              performed the same as for files, and when its done 
                              NewSID unloads the user hives it loaded. As a 
                              final step NewSID scans the HKEY_USERS key, which 
                              contains the hive of the currently logged-in user 
                              as well as the .Default hive. This is necessary 
                              because a hive can't be loaded twice, so the 
                              logged-in user hive won't be loaded into 
                              HKEY_LOCAL_MACHINE when NewSID is loading other 
                              user hives.

                              Finally, NewSID must update the ProfileList 
                              subkeys to refer to the new account SIDs. This 
                              step is necessary to have Windows NT correctly 
                              associate profiles with the user accounts after 
                              the account SIDs are changed to reflect the new 
                              computer SID.

                              NewSID ensures that it can access and modify every 
                              file and Registry key in the system by giving 
                              itself the following privileges: System, Backup, 
                              Restore and Take Ownership.
                               Using the Source
                               Full source code to NewSID has been provided for 
                              educational purposes. You may not use this code in 
                              a commercial or freeware SID-changing product, but 
                              you may use its techniques in other programs for 
                              private or commercial use.




