Transcript bh-win-03-riley

Surviving
OpenHack 4
Steve Riley and Timothy Bollefer
Microsoft Corporation
Yes we can
• Believe it!
• Any reasonably skilled administrator can build
a Windows environment that is secure and
resilient against attack
• You’ll learn today how we won the latest
OpenHack competition by eWeek
• You can use these principles today on your
own deployments
System components
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Web application
IIS 5.0
Windows 2000 AS
IPSec policies
Remote management and monitoring
SQL Server 2000
Passwords
• Keep this in mind: we used no firewalls!
Web application
Web application
• Built on eWeek’s eXcellence Awards web site
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User sets up account
Enters a product or service for judging
Submits a credit card number to pay entry fee
Read information about award
• Built with .NET Framework
• ASP.NET
• ADO.NET
• Cryptography class libraries
Web application
User authentication
• ASP.NET provides many options
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Integrated Windows authentication
Basic
Digest
.NET Passport
Client certificate
Forms (custom)
• eWeek requested forms
Web application
Forms authentication
• POST user name and password over SSL
• Use encrypted cookie to keep logon session
• Unauthenticated users can access home page
(and a couple others)
• Requests to secure pages get redirected to logon
page
Web application
Page protection
• Request forms authN with three lines of code
• <system.web> section of Web.config file in
application’s root folder
• Applies to all pages in application
• Protect certain pages in subfolder with a
little more code
• Add another Web.config here
• Inherits authN info from top-level file
• Denies access to unauthenticated users
Web application
Page protection—request authN
<authentication mode="Forms">
<forms loginUrl="Login.aspx"
name="OPSAMPLEAPP"/>
</authentication>
Web application
Page protection—required authN
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<system.web>
<authorization>
<deny users="?" />
</authorization>
</system.web>
</configuration>
demo
Web.config files
Web application
Account creation and login
• New account
• Encrypt password with 3DES
• Store in database with user name
• Login to existing account
• Encrypt password with 3DES
• Compare with encrypted password in database
• Create cookie and send to user
• System.Web.Security.FormsAuthentication class
• All over SSL
• Prevents replay attacks
Web application
Input validation
• Critically important security function
• Ensure user input doesn’t change
application’s behavior
• Helps guard against—
• Buffer overruns
• Cross-site scripting
• Malicious code execution
Web application
Input validation
• Requires multiple layers
• Plan for the worst
• Assume one or more tiers could be compromised
• Four checks
• Validate all field input
• Validate query string portion of URL
• Use stored procedures with type-checked
parameters
• HTML-encode all data sent to users
Web application
Input validation—1st check
• Two ASP.NET classes
• RegularExpressionValidator
• RequiredFieldValidator
• Limited input characters to space,
apostrophe, comma, period, letters, numbers
• Other characters blocked
• Commonly used to upload malicious code
Web application
Input validation—2nd check
• Parse URL query string
• System.Text.RegularExpressions.Regex
• Validate input with regular expression
• Allow numbers only
Regex isNumber = new Regex("^[0-9]+$");
if(isNumber.Match(inputData) ) {
// use it
}
else {
//discard it
}
Web application
Input validation—3rd check
• Use stored procedures for data access
• Limits app’s interaction with database
• Strongly-typed parameters
• Allowing web app to dynamically build
queries is baaaaad!
• Whacked web server  arbitrary code injection
• Input parameters are type-checked first
Web application
Input validation—4th check
• HTML encode all data sent back to user
• HtmlEncode method in
System.Web.HttpServerUtility class
• Prevents cross-site scripting attacks
• Compromise database  enter script in records 
return to user  execute in browser
• Script commands translated to harmless text
SomeLabel.Text = Server.HtmlEncode(username);
demo
Input validation code
Web application
Storing secrets
• Need to protect two kinds here
• Database connection/login string
• User password and credit card information
• Use different approaches for each
Web application
Storing secrets—connection string
• Web app needs to authenticate to database
• Usual method is to store ID/password in code
• Holy grail for an attacker
• Use integrated Windows authN
• String contains only server location and DB name
• Stored in “code-behind” file—core app logic
• Not user interface definition files
• Still not enough
• Attacker on physical machine could read file
• So…
Web application
Storing secrets—connection string
• Encrypt string using data protection API
(DPAPI) functions
• CryptProtectData and CryptUnprotectData
• Encrypts secrets without having to manage or
store keys
• Store string in registry
• ACL the registry key—
• Administrators
• ASPNET worker process
Web application
Storing secrets—user info
• DPAPI is less useful here
• Keys based on local machine information
• Each web server in the farm would have its own
key; can’t access shared info this way
Web application
Storing secrets—user info
• Generate 3DES encryption key and
initialization vector
• TripleDES class in
System.Security.Cryptography
• Symmetrically encrypt password and credit
card number stored in DB
• Salt: cryptographically strong random first block
• Encrypt key and IV with DPAPI and store in
ACLed registry on each web server
demo
Code for
storing secrets
Internet Information
Services 5.0
IIS 5.0
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Updated service packs and security patches
Moved default web site
Ran IISLockDown tool
Installed and updated .NET Framework
Remapped extensions
Configured account privileges and
permissions
• Installed URLScan
• Added ACLs to application folder and logs
IIS 5.0
Default web site location
• Move out of %systemdrive%\inetpub
• Put in different folder on different volume
• Attacker needs to see directory tree now
• Can’t access the system drive with ..\
IIS 5.0
IISLockDown
• Use static web server template
• No need for dynamic content types in this app
• Will modify in a bit
• Get it now:
http://microsoft.com/technet/security/tools/tools/lockto
ol.asp
IIS 5.0
.NET Framework
• Redistributable:
http://msdn.microsoft.com/downloads/sample.asp?url=/msdn
-files/027/001/829/msdncompositedoc.xml
• Service pack 2:
http://msdn.microsoft.com/netframework/downloads/updates
/sp/default.asp
• Latest hotfix (cred strengthening):
http://support.microsoft.com/default.aspx?scid=kb;enus;Q329250
• MDAC 2.7:
http://www.microsoft.com/data/download.htm
IIS 5.0
Remove extension mappings
• Need only .aspx and a few static content
types
• Remap other application extensions to
404.dll extension
• Included with IISLockDown
IIS 5.0
Account privileges and perms
• Use default local ASPNET service account
• Created during Framework installation
• Placed in Users local group
• Also receives—
• temporary ASP.NET folder: full
• %windir%\temp: full
• Framework installation folder: read
• Add this account to local Web application
group created by IISLockDown
• This group can’t run executables
• Update group’s perms to run the C# compiler and
resource converter
IIS 5.0
URLScan
• Part of IISLockDown
• Parser examines URL before passing it to IIS
• Configuration—
• Allow only the app’s extensions
• Block long requests
• More details:
http://www.microsoft.com/technet/security/tools/tools/ur
lscan.asp
IIS 5.0
Folder and log ACLs
• Web content folders—
• ASP.NET worker process: read
• Anonymous: read-only on served content
• Log folders—
• System account and Administrators group only
• All others: deny
• IIS and URLScan logs
demo
IISLockDown
Extension remapping
Accounts
URLScan
Folder/log ACLs
Windows 2000
Advanced Server
Windows 2000 AS
• Updated service packs and security patches
• Disable unused OS services
• Various registry-based tightenings
Windows 2000 AS
Unused services
Baseline template disables these:
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Alerter
Appmgmt
Bits
Browser
Clipsrv
Dfs
Dhcp
Fax
Ismserv
Kdc
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Messenger
Mnmsrvc
Msdtc
Netdde
Netddedsdm
Ntfrs
Rasauto
Rasman
Remoteregistry
Sharedaccess
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Spooler
Tapisrv
Tlntsvr
Trksvr
Trkwks
Utilman
Winmgmt
Wmi
Wuauserv
Windows 2000 AS
Unused services
• SQL Server
• Lanmanserver—manual
• Sqlserveragent—disabled
• Terminal server
• Lmhosts—disabled
• Web server
• Lanmanserver—disabled
• VPN server
• Rasauto, Rasauto, Lmhosts, Tapisrv,
Remoteregistry—automatic
Windows 2000 AS
Reg tweaks—NoLMHash
HKLM\System\CurrentControlSet\
Control\LSA
• Prevents Windows from storing LM hash
format passwords
• Susceptible to decryption
• Key in Windows 2000; value in Windows XP
and Server 2003
Windows 2000 AS
Reg tweaks—NoDefaultExempt
HKLM\System\CurrentControlSet\
Services\IPSec
• IPSec normally exempts Kerberos traffic from
policy engine
• Change default so that no traffic is allowed
from source port 88
• See IPSec section for more details
Windows 2000 AS
Reg tweaks—DisableIPSourceRouting
HKLM\System\CurrentControlSet\
Services\Tcpip\Parameters
• Prevents an application from specifying a
route in an IP packet
• Enforces use of computer’s default gateway
• Eliminates certain man-in-the-middle attacks
Windows 2000 AS
Reg tweaks—SynAttackProtect
HKLM\System\CurrentControlSet\
Services\Tcpip\Parameters
• Limits system resources allocated to incoming
requests
• Prevents certain SYN-flood attacks and
denials of service
demo
Registry tweaks
IPSec policies
IPSec policies
• Traffic requirements
• Web server  SQL Server
• RAS  management net over L2TP
• Mgmt server  clients for Terminal Services and
file sharing
• Mgmt server  all servers over private NICs
• All servers  mgmt server file shares
IPSec policies
Protection
• Use digital certificates for authentication
• Standalone CA taken offline after machine
enrollment
• Signed (SHA-1)
• Between all computers; enforces machine-tomachine authentication
• Protects integrity
• Encrypted (MD5)
• To/from management server
• Protects confidentiality of internal traffic if frontend were compromised
IPSec policies
Policy properties
• Initial config on all servers
• Block all IP and all ICMP traffic
• Web server  SQL Server
• “Authenticate and sign” action: IPSec AH
• Mgmt server  everything
• “AuthN, sign, encrypt” action: IPSec ESP+AH
• Internet  web servers
• Permit
IPSec policies
Relationships
demo
IPSec UI—
each server’s policy
Remote management
and monitoring
Remote management
• An OH requirement is to show it’s possible to
update the app during the contest
• Our solution:
• L2TP+IPSec remote-access VPN
• Terminal Services
• Restricted file shares
Remote management
L2TP+IPSec remote-access VPNs
• L2TP is the tunnel; IPSec encrypts it
• Remote administrator needs—
• Computer certificate trusted by RRAS server
• Remote access account credentials
• Achieve trusted computer and user
• Computer certificate is non-exportable
• We know where the user is coming from
• User account to log on to RRAS (and TS)
• We know who the user is
Remote management
Terminal Services
• Individual accounts on each computer (no
domain here)
• Password strength described later
• TS access limited to OHTS computer only
• Carried over the VPN
• Although TS traffic is already encrypted
• From OHTS can connect to TS on other
computers
• “Nesting” TS works just fine
Remote management
File shares
• “inbox” share
• To drop off changed site content
• Write-only
• “outbox” share
• To retrieve files for analysis
• Read-only
Remote management
Physical network
demo
VPN configuration
SQL Server 2000
SQL Server 2000
• It’s all about reducing the “surface area”
exposed to attackers
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Installed software
Authentication
Service account
Communications protocols
Recovery actions
Application permissions
SQL Server
Installed software
• Service pack 2 and latest security patches
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Upgrade tools
Debug symbols
Replication support
Books online
Development tools
• Disable—
• Msdtc
• SQL Server agent
• Microsoft search
SQL Server
Authentication
• Modified local security policy to allow
NTLMv2 only
• Configure for Windows only
• No need to store SA ID/password on web server
• Set huge SA password
• In case someone “accidentally” changes authN
• Set audit level to “Failure”
• Good evidence of attempted attack forensics
• But if attacker did figure out password, how would
you know…?
• Maybe should audit success and failure
SQL Server
Service account
• Default is LocalSystem
• Has too many permissions!
• Create local user account for SQL service
• Strong password
• User can’t change
• No TS access
• Or can use domain user account if network
access is necessary
SQL Server
A couple others
• Communications protocol
• In server network utility: hide SQL Server from
client broadcasts
• Remove named pipes protocol (need TCP/IP only)
• Recovery actions
• Set to “restart the service”
• In service properties page
• More of a reliability thing…
SQL Server
Application permissions
• Delete sample Northwind and Pubs databases
• Create application database
• Grant app account permissions on stored
procedures but on the tables themselves
• Prevents execution of ad hoc SQL queries
• Ensure this account has no permissions anywhere
else in SQL Server
demo
SQL Server configuration
Passwords
Passwords
• Do we even need to mention this? ;)
• Include characters from at least three—
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Lowercase alphabet
Uppercase alphabet
Numbers
Non-alphanumerics
• The super-paranoid should use all four plus
ALT+??? symbols
• Go for length
Learnings
Learnings
• Every deployment is unique, but certain
principles apply everywhere
• Use, adapt, modify as necessary
• Need to state the obvious here (after all, this
is a PowerPoint presentation…)
The obvious
• Plan for security in the original design
• Always install latest service packs and patches
(design should include plan for this)
• Always use complex non-intuitive passwords
• Reduce surface area by disabling unnecessary
functionality
• Adhere to the principle of least privilege
• Anticipate failure; practice defense in depth
• Always run IISLockDown and URLScan on IIS
• Validate all input data
• Use only parameterized stored procedures on a
database
© 2003 Microsoft Corporation. All rights reserved.
This presentation is for informational purposes only. MICROSOFT MAKES NO WARRANTIES, EXPRESS OR IMPLIED, IN THIS SUMMARY.