Protect yourself against future threats.
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AUSCERT External Security Bulletin Redistribution
ESB-2003.0054 -- UNIRAS ALERT - 03a/03
Serious Worm Activity update
26 January 2003
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AusCERT Security Bulletin Summary
---------------------------------
Product: MS-SQL Server
Vendor: Microsoft
Operating System: Windows
Impact: Execute Arbitrary Code/Commands
Denial of Service
Access Required: Remote
Ref: AU-2003.002
ESB-2003.0053
ESB-2002.368
ESB-2002.364
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UNIRAS (UK Govt CERT) ALERT - 03a/03 dated 25.01.03 Time: 13:50
UNIRAS is part of NISCC(National Infrastructure Security Co-ordination Centre)
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UNIRAS material is also available from its website at www.uniras.gov.uk and
Information about NISCC is available from www.niscc.gov.uk
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VNA reference : http://www.ngssoftware.com/vna/ms-sql.txt
Description
***********
Microsoft's database server SQL Server 2000 exhibits two buffer overrun
vulnerabilities that can be exploited by a remote attacker without ever having
to authenticate to the server. What further exacerbates these issues is that
the attack is channeled over UDP. Whether the SQL Server process runs in the
security context of a domain user or the local SYSTEM account, successful
exploitation of these security holes will mean a total compromise of the target
server and its data.
Details
*******
SQL Server can be configured to listen for incoming client connections in several
different ways. It can be configured such that clients can use named pipes over
a NetBIOS session (TCP port 139/445) or sockets with clients connecting to TCP
port 1433 or both. Which ever method is used the SQL Server will always listen
on UDP port 1434. This port is designated as the Microsoft SQL Monitor port and
clients will send a message to this port to dynamically discover how the client
should connect to the Server. This message is a single byte packet, the byte
being 0x02.
There are other messages that can be sent to this port and these can be worked out
with simple experimentation.
Stack Based Buffer Overflow
*********************************
When SQL Server receives a packet on UDP port 1434 with the first byte set to 0x04,
the SQL Monitor thread takes the remaining data in the packet and attempts to open
a registry key using this user supplied information. For example, by sending
\x04\x41\x41\x41\x41 (0x04 followed by 4 upper case 'A's) SQL Server attempts to
open
HKLM\Software\Microsoft\Microsoft SQL Server\AAAA\MSSQLServer\CurrentVersion
By appending a large number of bytes to the end of this packet, whilst preparing the
string for the registry key to open, a stack based buffer is overflowed and the
saved return address is overwritten. This allows an attacker to gain complete control
of the SQL Server process and its path of execution. By overwriting the saved return
address on the stack with an address that contains a "jmp esp" or "call esp"
instruction, when the vulnerable procedure returns the processor will start executing
code of the attacker's choice. At no stage does the attacker need to authenticate.
Heap Based Buffer Overflow
********************************
When SQL Server receives a packet on UDP port 1434 with the first byte set to 0x08
followed by an overly long string, followed by a colon character (:) and number a heap
based buffer is overflowed. As this corrupts the structures used to keep track of the
heap an attacker can overwrite any location in memory with 4 bytes of their own choosing.
This can be used to gain remote control of the processes execution. If the colon and
number are missing the SQL Server process access violates before the heap is corrupted
as the code in the SQL Monitor thread fails to handle exceptions.
For example the code calls the C function strtok(). The strtok() functions looks for a
given token in a string, in this case a colon, and if found returns a pointer to it. If
the colon is missing in the string being searched then no pointer is returned. This is
one of the reasons why the SQL Server process access violates if the colon is missing.
The code does not check to see if a valid pointer has been returned before passing it
to another function call, atoi():
char *ptr=NULL;
int num=0;
..
ptr = strtok(string,":");
num = atoi(ptr); // ptr is used without being validated
Failure to check return values and handle exceptions leads to the process dying, leading
to a simple Denial of Service attack. That said, in the light of the overflows, the DoS
is the least of the problems.
Network Based Denial of Service
*************************************
When an SQL Server receives a single byte packet, 0x0A, on UDP port 1434 it will reply to
the sender with 0x0A. A problem arises as SQL Server will respond, sending a 'ping'
response to the source IP address and source port. This 'ping' is a single byte UDP
Packet - 0x0A. By spoofing a packet from one SQL Server, setting the UDP port to 1434,
and sending it the a second SQL Server, the second will respond to the first's UDP port
1434. The first will then reply to the second's UDP port 1434 and so on. This causes a
storm of single byte pings between the two servers. Only when one of the servers is
disconnected from the network or its SQL service is stopped will the storm stop. This
is a simple newtork based DoS, reminiscent of the echo and chargen DoSes discussed back
in 1996 (http://www.cert.org/advisories/CA-1996-01.html). When in this state, the load
on each SQL Server is raised to c. 40 - 60 % CPU time.
Considerations for protection against these vulnerabilities
********************************
Exploitation of these security holes goes over UDP, a connection-less communications
protocol. As such it makes the task of bypassing the protection offered by a firewall
considerably easier. The spoofing of an IP address in a UDP packet is also considerably
easier.
It is trivial for an attacker to send an attack through the firewall, setting the source
IP address to that of the target's DNS Server and the source port to 53. Most firewalls
will allow this packet through as it will look like a response to a query to resolve a
domain name.
It is strongly recommended that a rule be added to each organization's firewall such that
any packet destined for UDP port 1434 on the 'clean' side of the firewall be dropped and
logged. No host, even DNS Servers, should be allowed to send traffic to this port.
It is also recommend that firewall administrators ensure that any packet received on the
'dirty' interface with a source IP address set to an address on the clean side is also
dropped and logged.
Fix Information
***************
NGSSoftware alerted Microsoft to this problem on the 17th of May 2002 and they have
produced a patch that resolves these issues. NGSSoftware urge all customers of SQL Server
2000 to test then apply these fixes as soon as possible.
http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS02-039.asp
Where possible, NGSSoftware also recommend running the SQL Server as low privileged local
account and not SYSTEM or a domain account.
NISCC recommends blocking ingress and egress traffic on ports 1433, 1434 and 1435
as well as the above advice as there have been reports of the worm probing the above
listed ports. If anyone uses Cisco netflow keep a track on the flows to catch infected
hosts.
This worm lives only in memory (like code red) so to fix the problem reboot and patch
(download the patch first though!).
Most ISPs are now filtering the traffic associated with port 1434 and this is showing
a decrease in overall traffic.
If anyone would like to block on file size or particular strings the following from
NAI will help: The malformed packet is 376 bytes long and carries the following
strings: "h.dllhel32hkernQhounthickChGetTf", "hws2", "Qhsockf" and "toQhsend".
Thanks to Rob Thomas and to NEXTGen and NAI
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For additional information or assistance, please contact the HELP Desk by
telephone or Not Protectively Marked information may be sent via EMail to:
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Tel: 020 7821 1330 Ext 4511
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UNIRAS is a member of the Forum of Incident Response and Security Teams (FIRST)
and has contacts with other international Incident Response Teams (IRTs) in
order to foster cooperation and coordination in incident prevention, to prompt
rapid reaction to incidents, and to promote information sharing amongst its
members and the community at large.
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<End of UNIRAS Briefing>
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