sql server security - attack

04/12/23 www.sqlsecurity.com 1

SQL Server Security

Attack & Defense

Chip Andrews (www.sqlsecurity.com)

January 2003

AtlantaMDF Users Group


Presentation Outline

• Introduction• Attack

– Fingerprinting– Account Acquisition– Privilege Escalation– SQL-Injection

• Defense– Tools (Scanners/Patches)– Hardening Scripts– Secure Deployment– Input Validation– Best-Practices


SQL Server Presence

• Biztalk Server 2000• Commerce Server 2000• Application Center Server 2000• Third-Party Apps (SQL/MSDE)

– Tumbleweed Worldsecure– Valadeo Technologies, Inc.– O’Reilly & Associates, Inc. (WebBoard)– Telemate.net

• Hierarchical File systems looming in the future (rumored link between Yukon and Longhorn development)


MSDE Proliferation

Microsoft SQL Server Desktop Engine (formerly the Microsoft Data Engine)• Development methodologies (agile) often suggest

each developer (or team) have a local database instance – http://martinfowler.com/articles/evodb.html

• Visual Studio.NET installs MSDE (vsDotNet/NetSDK)

• .NET Framework SDK (required for samples)• Office XP


Section 1 - Attack

• Fingerprinting/Discovery

• Acquiring Access

• Privilege Escalation

• Backdoors

• Covering tracks


Discovery - Target Acquisition• Server fingerprinting via IP stack identification

– Nmap/nmapnt – www.insecure.org/nmap– www.eeye.com

• IIS Web Servers - a good bet SQL Server is driving it– telnet targetname 80– HEAD / HTTP/1.0– www.netcraft.com

• Dig for hints about target database usage– Newsgroups

• Groups.google.com• SQL discussion boards (www.swynk.com)

– Job Postings• Corporate website (click ‘careers’)• www.monster.com etc.


Discovery - Port Scanning

• Use nslookup / whois to determine IP addresseswhois “target.”@whois.arin.net

• TCP port 1433 (and 2433)– SQL Server defaults to listen on these ports since ip-

sockets net-lib is installed by default (along with named pipes)

– Hosting providers are particularly juicy targets

• UDP port 1434 (SQL Server Resolution Service)


SQL Server Discovery – UDP 1434

• Multiple instancing capabilities of SQL Server 2000 make enumeration a functional requirement

• A specially formed UDP packet directed at port 1434 will cause the SQL 2K listener service to divulge information about every instance of SQL Server running on that machine– Packet Information

• Version (Inaccurate – does not show patch level)• Instance names• Net-libs supported• TCP ports and pipe names • Clustered status (bullseye!)


Broadcast Discovery

• Since the listener may exist on multiple machines, it is possible to send a broadcast UDP packet to port 1434 to discover all instances of SQL Server 2000 on a subnet– Osql –L (will return a raw listing) but only of server

names and only via broadcast to 255.255.255.255– Network subnets such as 192.168.1.x (with a

255.255.255.0 mask) can be scanned using a single packet directed at 192.168.1.255

– Any network class works find (Class A, B, C)


SQLPing Utility

• Directs a custom udp packet at a specific target or subnet and enumerates the server info across multiple instances

SQLPinging 192.168.1.255

Listening....

ServerName:LANDROVER

InstanceName:SQL2K

IsClustered:No

Version:8.00.194

tcp:1241

np:\\LANDROVER\pipe\MSSQL$SQL2K\sql\query

ServerName:LANDROVER

InstanceName:MSSQLServer

IsClustered:No

Version:7.00.623

np:\\LANDROVER\pipe\sql\query

tcp:1433

rpc:LANDROVER

http://www.sqlsecurity.com


Discovery – Service Enumeration

sc \\machine_name query bufsize= 60000|find “MSSQL” • Requires Windows authenticated user and

NetBIOS connectivity• Easily scriptable (replace machine name with IP

address)• Provides a way to see where SQL Servers exist on

hosts even the server is not running or SQL TCP ports have been blocked


Account Acquisition• Common Accounts

– Sa (In the name of all that is holy – do not leave this blank)

– distributor_admin (nor this one…)

• Brute Force (mixed security model)– Attacks the inherent weakness of the native SQL Server

security model– Multiple freeware tools (sqldict, sqlpoke,sqlbf)– Mssqlserver lacks account lockouts or password

complexity requirements– Do we even need to mention null ‘sa’ account

passwords?


Account Acquisition (cont.)• Connection strings (mixed mode)

– Client registry (regedit)– Imbedded in ASP source or client-side script (RDS)– Config files (global.asa, connect.inc, web.config)

• Source code disclosure– IIS has had plenty (online.securityfocus.com)

• Sniffing (mixed or NT security mode)– Wifi networks – L0phtcrack (to obtain NT account)– Sniffing SQL (TCP 1433) traffic (non SSL/RPC)

• Plaintext transmission of credentials• Passwords trivially obfuscated (combination of Unicode sprinkled

with an XOR operation)


De-obfuscating SQL Server Passwords

Hex A2 B3 92 92

Swap Digits

2A 3B 29 29

Binary 0010 1010 0011 1011 0010 1001 0010 1001

5A 0101 1010 0101 1010 0101 1010 0101 1010

XOR 0111 0000 0110 0001 0111 0011 0111 0011

Hex 70 61 73 73

Text P a s s


Account Acquisition - SQL Injection

Defined: The introduction of unintended SQL code to an application’s database at runtime.

• This effectively provides an attacker with a SQL Server account by using your application as a middle-man in the attack

• SQL injection attacks rarely alerts IDS systems (worsened by SSL)

• Difficult to track down all the areas of exploitation since the only real solution is manual code review

• No amount OS security, firewalls, patch diligence will stop SQL injection.

• The best solution is good coding practices


SQL Injection Sample

• ASP Code Sample<%

Set Conn =

Server.CreateObject("ADODB.Connection")

Conn.open “dsn=myapp;Trusted_Connection=Yes“

Set RS = Conn.Execute("SELECT * from book_list where book_name=‘" & request.form(“txtBookname”) & “’)

%>


SQL Injection Sample Cont.

• Consider if the attacker searches for a book named: ‘ union select name from sysobjects--

• Single quote closes the intended statement• Union statement appends a new dataset to the

query so the attacker can see information he wants• Could just as easily call any stored procedure or

DDL command the attacker wanted given appropriate level of privilege


SQL Injection - Tricks

• Tricks attackers use– UNION statements to append data ripped from other SQL– “—” double hyphen comment indicator to block out the rest of the

intended SQL– Try a single quote in input fields to see if the query fails (failure usually

indicates bad input validation and possible exploitation)

– exec master..xp_cmdshell ‘ping HACKER_IP’ to check for ‘sa’-level exploitable hosts

– select name from sysobjects where type = ‘u’ can expose tables to exploit

– Insert tablename exec sp_whatever – good way to see output of stored procedures

– Use @@version to return SQL Server and OS versions and Service Packs


Account Acquisition – Buffer Overflows

• By overflowing buffers on listening ports it is possible to gain a system shell on an un-patched target server with the privilege level of the SQL Server service account (often LocalSystem)

• There are known attacks against both the SQL Resolution service by David Litchfield (http://online.securityfocus.com/bid/5311 ) and the TCP SQL Service listener “Hello Bug” by Dave Aitel (http://lists.insecure.org/lists/pen-test/2002/Aug/0016.html)

• Exploit code for both is “in the wild”• Buffer overflows exist externally as well as internally

(privilege escalation) through server functions and extended stored procedures


Privilege Escalation

• Primary methods– Un-patched Server bugs such as

• _Many_ extended stored procedure privilege escalation attacks

• Multiple Openrowset vulnerabilities

• Check online.securityfocus.com/bid for the latest

– Trojan stored procedures (sp_who for example)– Deferred compilation (EXECUTE)


Privilege Escalation (cont.)• Other methods

– xp_regread (registry enumeration)• Any normal user can see the service context via

master..xp_regread 'HKEY_LOCAL_MACHINE' ,'SYSTEM\CurrentControlSet\Services\MSSQLSERVER','ObjectName'

– Openrowset – heterogeneous queries can allow attackers to brute-force their way into other systems

– Errors in extended stored procedures and system stored procedures• SQLAgent Jobs - http://www.ngssoftware.com/advisories/mssql-

esppu.txt • Webtasks

http://www.ngssoftware.com/advisories/mssql-webtasks.txt • The list goes on….

– See online.securityfocus.com for a complete listing– Bottom Line: if you are not keeping up with patches then any user

with SQL Server access can trivially elevate privilege unless extensive steps have been taken


They’re in as sysadmins - Now What?

• Create a backdoor SQL or NT account

• Insert trojan extended stored procedures to capture passwords/data/events

• Use tftp to pull in toolkits

• Use this SQL Server to launch attacks against other hosts

• Install proxy server to make this machine a platform for further attackers on other systems

• Take your data and make you suffer

• As usual – possibilities are limited only by the imagination


Attack Conclusion• Take time to put yourself in the place of someone who

really wants to get at you or your employer– How far can you get?– What if the attacker is a former employee?– Do our defenses match the threat and risk levels?– Would be even be aware if we were under attack?

• Scan your networks and determine what people on the inside and the outside can access

• Brute-force your own systems to be sure password complexity and account policies (if using Windows security) are sufficient– Multitude of free tools at www.sqlsecurity.com


Defense

• What can you do to protect against each level of attack?

• How do I keep up to date with patches without an army of admins?

• What are some general defensive guidelines?

• What is the best defense for each type of SQL Server deployment?


Secure Installation/Configuration• Lockdown scripts (www.sqlsecurity.com)

– Check service context– Check patch level– Set mode to Windows Authentication– Assign long, random ‘sa’ account password– Enable authentication auditing– Disable SQLAgent, Microsoft Distributed Transaction Coordinator

(MSDTC), and MSSEARCH– Disable adhoc queries on all providers– Remove sample databases– Tighten permissions on master/msdb database objects– Increase log history– Delete temp files used for install/upgrades


Discovery Defense• Block UDP 1434 inbound

– BOL says you cannot do this but you can– Remember that named instances must be port configured on client

• Firewall connections from all untrusted clients by IP address• Remove un-needed netlibs• Keep credentials out of connection strings• Unfortunately the “Hide Server” option in TCP/IP properties

does not help– TCP port forced to 2433– If any other netlibs are installed the server will still respond to UDP

1434 calls


Account Acquisition Defense• Strong password enforcement

– Entropy, Lifetime, Length

• Enable auditing (at least failed logins)• Encrypt all sensitive traffic

– SSL recommended – Multi-protocol encryption not recommended

• No multiple instance support (instances only supported on Named Pipes, TCP/IP, NWLink, and Shared Memory netlibs)

• RPC encryption API only – weaker key management

• Keep credentials out of connection strings and encrypted when possible

– DPAPI (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnnetsec/html/SecNetHT08.asp)

– Use Windows Auth when possible


Privilege Escalation Defense• Especially important to KEEP CURRENT WITH

PATCHES– Perform custom scripting if need-be– Use Commercially available patch tools

• HFNetChk Pro - www.shavlik.com• UpdateExpert – www.stbernard.com • Service Pack Manager 2000 - www.securitybastion.com

– Write Microsoft at [email protected] and emplore them to:

• Include SQL Patches in Windows Update• Perform patches to all instances on demand• Make SQL Server patch installs more user-friendly


Privilege Escalation Defense• As an admin, never run user-created stored procedures and functions

without inspecting it first– This can be particularly problematic when users encrypt stored procedures (see

www.sqlsecurity.com for tools to decrypt)

• Run extended stored procedures using fully-qualified designation (master.dbo.xp_cmdshell)

• Block access to public role to all procedures that could be abused (submit suggestions for Lockdown Script)

• No longer recommending the “dropping” of extended stored procedures– Complicates Service Pack Installations– Breaks vital SQL Server mechanisms such as the use of Enterprise Manager,

Query Analyzer, and Profiler– Could break as Microsoft introduces new functionality


SQL Injection Defenses: Input Validation

• Scrub input data to make sure it contains only acceptable charactersreplace(inputstring,’,’’) Remove single quotes to help

prevent quote-closing attacks

Set myregex = new regexp

myregex.global = True myregex.pattern = “\W+”

cleaninput=myregex.replace

Remove all characters except a-zA-Z0-9

Set myregex = new regexp

myregex.global = True

myregex.pattern = “\D+”

cleaninput=myregex.replace

Numbers only


Input Validation – Stored Procedures

• Stored procedures can help enforce stronger typing but using them at every database access can be brutal due to the sheer number of procs that may need to be created or because of application requirements

– Since SQL Server has already compiled the query plan for the query, no further code injection is possible if we properly invoke the procedure

Create procedure sp_login

@username varchar(20),

@password varchar(20)

AS

Select * from users where username = @username and password = @password


Secure Implementation of SP• Use SqlCommand and SqlParameter objects to explicitly identify parameters

SqlConnection cn = new SqlConnection(yourConnectionString);SqlCommand cmd = new SqlCommand("usp_authors", cn);

// Mark the Command as a SPROCcmd.CommandType = CommandType.StoredProcedure;

// Add Parameters to SPROCSqlParameter prmLast = new SqlParameter("@last", SqlDbType.VarChar,50);prmLast.Value = TextBox1.Text;cmd.Parameters.Add(prmLast);

// Create and Fill the SqlDataReadercn.Open(); SqlDataReader dr = cmd.ExecuteReader(CommandBehavior.CloseConnection);

• Use the same method even for text command types. Do not use string concatenation to build query strings.


Discipline

• Make sure developers adhere to the standards– Develop a methodology

• Command/Parameter objects / stored procs

• No access to production servers

• Consistent database access and developer education

– Encourage reusable security components

– Code review

– QA Test Plans

– Code with an intruder’s mindset


Best Practices

• Use principle of least-privilege• Assign MSSQLServer service non-

administrator user context• Take the time to properly implement trusted

security (Windows Auth Mode)• Don’t place passwords in script/code• Assign complex ‘sa’ password even when

using Windows Authentication


Best Practices (cont.)• Write re-usable input validation routines and make

their use mandatory• Use stored procedures wherever possible but avoid

“string building” for executing them• Code reviews are an absolute necessity• Evaluate third-party code and applications with

great scrutiny• Use SSL or IPSec to encrypt network traffic on

suspect subnets (more applicable to client/server deployments but a powerful option)


Special Consideration : MSDE• MSDE Difficulties

– Stealth install – users rarely aware it exists– Defaults to over-privileged LocalSystem security context– Separate service pack download– Multiple MSDE installer editions (the MSI file used to

install – KB Q311762)– If you used any of the 15 other MSI installers besides

sqlrun01.msi you must order an upgrade CD from Microsoft to apply a service pack

– No tools to easily modify netlibs, audit level, security mode, or anything else for that matter


Deployment Solutions: 1 - MSDE and Single User

• Remove ALL netlibs w/Server Network Utility orEXECUTE master.dbo.xp_regwrite N'HKEY_LOCAL_MACHINE',N'SOFTWARE\Microsoft\

MSSQLServer\MSSQLServer\SuperSocketNetLib', N'ProtocolList',N'REG_SZ',’’Or (for non-default instances)EXECUTE master.dbo.xp_regwrite N'HKEY_LOCAL_MACHINE', SOFTWARE\Microsoft\

Microsoft SQL Server\(instance_name)\MSSQLServer\SuperSocketNetLib’, N'ProtocolList',N'REG_SZ',’’

– Local connections allowed only through the shared memory netlib (which cannot be removed)

– User (local) or . To specify the server name in connection strings

– Secure, lightweight, simple– Can easily restore netlibs temporarily if need be

• Lockdown scripts


Special Deployment Solutions 2 : Web-Based Applications (Forms Auth)

• Use Windows Authentication mode in SQL Server – Alter IIS Metabase for Anonymous access specifying a low-priv local or

domain user account– If local user is used, make sure same account/password exist on SQL Server– Turn of “Allow IIS to Control Password” option as this uses iissuba.dll and

defeats ability to authenticate to the SQL Server– ASP.NET : aspnet_wp process runs in context specified in web.config or

machine.config. Look for processModel key – userName attribute. (note that when an ASP.NET app runs with impersonation, this will cause authentication to occur using impersonated context and not the service context)

• Block ALL direct access to SQL Server except through web server and secure back-end systems (inbound only)

• Encrypt data using asymmetric encryption methods using public key only – never store private key on this server

• All this does *NOT* defeat connection pooling since SQL Server user context is always the same


Special Deployment Solutions 3 : Client/Server Deployments

• Patches especially important due to direct access issues• Implement SSL as a means of protecting data/credentials in-transit

– Use a private CA to issue server certificate for the SQL Server– Clients will not be able to connect without certificate in local “trusted” store

(assuming SQL Server is requiring SSL)

• Application roles can be used to control access but this can also be achieved through the use of views and stored procedures which provide other benefits

• Be aware the application role activation (sp_setapprole) passwords are stored on the client (they cannot be invoked via a stored procedure) so reverse engineering can yield the role password which would give the attacker access to whatever the role can access


New at SQLSecurity.com

• SQLPing.NET– C# version of SQLPing. Source code included so

functionality can be integrated into other applications

• SQL Server Tools Listing (Free and Commercial)• Lockdown Script Project

– I am soliciting feedback from anyone who wants to help

• Full SQL Server Version list (thanks to Ken Klaft)


Recommended Reading• (*)Birkholz. Special Ops: Host and Network Security for Microsoft, UNIX, and

Oracle. Syngress, 2003.• (*)McClure, Scambray, and Kurtz. Hacking Exposed: Windows 2000. Osborne,

2001.• Lewis, Morris. SQL Server Security Distilled. Curlingstone, 2002.• Howard, Levy, and Waymire. Designing Secure Web-Based Applications for

Microsoft Windows 2000. Microsoft Press, 2000.• Rain Forest Puppy – Phrack Magazine Volume 8, Issue 54 Dec 25th, 1998, article 8

of 12.• David Litchfield. Remote Web Application Disassembly With ODBC Error

Messages http://www.blackhat.com/presentations/win-usa-01/Litchfield/BHWin01Litchfield.doc

• LeBlanc, Howard. Writing Secure Code. Microsoft Press, 2001.• McClure, Shah. Web Hacking. Addison Wesley, 2003.

(*) Books to which I have contributed chapters

sql server security - attack

Documents

sql server account

instance of sql server

instances of sql server

sql server defaults

sql server discovery

sql servers

sql server resolution

server names