File and Directory Access 06-1. How is file and directory security enforced? 06-2. What is NTFS? 06-3. Are there are vulnerabilities to NTFS and access controls? 06-4. What is Samba and why is it important? 06-5. I hack remotely. Once in, how can I do all that GUI stuff?
06-1. How is file and directory security enforced?
Since files and directories are considered objects (same as services), the security is managed at an "object" level.
An access-control list (ACL) contains information that controls access to an object or controls auditing of attempts to access an object. It begins with a header contains information pertaining to the entire ACL, including the revision level, the size of the ACL, and the number of access-control entries (ACEs) in the list.
After the header is a list of ACEs. Each ACE specifies a trustee, a set of access rights, and flags that dictate whether the access rights are allowed, denied, or audited for the trustee. A trustee can be a user account, group account, or a logon account for a service program.
A security descriptor can contain two types of ACLs: a discretionary ACL (DACL) and a system ACL (SACL).
In a DACL, each ACE specifies the types of access that are allowed or denied for a specified trustee. An object's owner controls the information in the object's DACL. For example, the owner of a file can use a DACL to control which users can have access to the file, and which users are denied access.
If the security descriptor for an object does not have a DACL, the object is not protected and the system allows all attempts to access the object. However, if an object has a DACL that contains no ACEs, the DACL does not grant any access rights. In this case, the system denies all attempts to access the object.
In a SACL, each ACE specifies the types of access attempts by a specified trustee that cause the system to generate audit records in the system event log. A system administrator controls the information in the object's SACL. An ACE in a SACL can generate audit records when an access attempt fails, when it succeeds, or both.
To keep track of the individual object, a Security Identifier (SID) uniquely identify a user or a group.
A SID contains:
A privilege is used to control access to a service or object more strictly than is normal with discretionary access control. Privileges provide access to services rarely needed by most users. For example, one type of privilege might give access for backups and restorals, another might allow the system time to be changed.
06-2. What is NTFS?
NTFS is the Windows NT special file system. This file system is tightly integrated into Windows security -- it is what allows access levels to be set from the directory down to individual files within a directory.
06-3. Are there are vulnerabilities to NTFS and access controls?
Not so much vulnerabilities as there are quirks -- quirks that can be exploited to a certain degree.
For example, let's say the system admin has built a home directory for you on the server, but has disallowed the construction of directories or files that you wish to make available to the group Everyone. You are wanting to make this special directory so that you can easily retrieve some hack tools but you are cut off. However, if the sys admin left you as the owner of the home directory, you can go in and alter its permissions. This is because as long as you are the owner or Administrator you still control the file. Oh sure, you may get a few complaints from the system when you are doing it, but it can be done.
Since NTFS has security integrated into it, there are not too many ways around it. The main one requires access to the physical system. Boot up the system on a DOS diskette, and use NTFSDOS.EXE. It will allow you to access an NTFS volume bypassing security.
The last quirk is that if you have a directory with Full Control instead of RWXDPO permissions, then you get a hidden permission called File Delete Child. FDC cannot be removed. This means that all members of the group Everyone can delete any read-only file in the directory. Depending on what the directory contains, a hacker can replace a file with a trojan.
06-4. What is Samba and why is it important?
Samba is a freeware app developed by Andy Tridgell. It is a great tool for helping integrate Unix into Microsoft Windows and Lan Manager environments. The main idea is that you can, with Samba, allow a Unix machine to access file and directories. The other handy thing about Samba is that like most Unix freeware you get the source code.
Most hackers seem to have Linux up and running, so loading up Samba allows you several tactical advantages. A number of the exploits described here require access to a privileged port (< 1024). If you are root on your own Linux box, you can start exploits from those needed ports. A lot of the tests in the NMRC lab were conducted using Samba. In fact when World Star Holdings Ltd in Canada had their lame Cybertest '96 contest on June 12th, yours truly used Samba to break in (but I wasn't first).
Samba talks SMB and can directly access Windows NT hardware, and Hobbit (email@example.com) has put together a very interesting paper entitled "CIFS: Common Insecurities Fail Scrutiny". It is highly recommended reading for admins and hackers alike. Included in the paper are details and source patches to allow easier attacking on NT.
Studying the source code of Samba taught me a lot, but Hobbit's paper puts everything in a whole new light. It provides some well documented basics on how a lot of the communications work, detailing exactly WHY certain protocols and behaviours are vulnerable to abuse.
Get Samba and read its documentation. Read Hobbit's paper and apply the patches. Period.
06-5. I hack remotely. Once in, how can I do all that GUI stuff?
The main problem is adjusting NT file security attributes. Some utilities are available with NT that can be used, but I'd recommend using the NT Command Line Security Utilities. They include:
saveacl.exe - saves file, directory and ownership permissions to a file restacl.exe - restores file permissions and ownership from a saveacl file listacl.exe - lists file permissions in human readable format swapacl.exe - swaps permissions from one user or group to another grant.exe - grants permissions to users/groups on files revoke.exe - revokes permissions to users/groups on files igrant.exe - grants permisssions to users/groups on directories irevoke.exe - revokes permissions to users/groups on directories setowner.exe - sets the ownership of files and directories nu.exe - 'net use' replacement, shows the drives you're connected to
The latest version can be found at ftp://ftp.netcom.com/pub/wo/woodardk/.
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