The Kraw Daemon HeadQuarter

We present an examination of the Conficker worm using dynamic and static analyses. Conficker is one of several new strains of malware, which has been aggressively spreading across the Internet since November 2008. Using static analysis, we dissect various aspects of the program logic, including its date-based triggers, domain generation logic, data validation function, and overall program structure. We compare various aspects of the two variants of Conficker, variants A and B. We analyze Conficker network communications and present results from our census of both A and B drones. Finally, we examine the question of attribution, and discuss some clues to its operation that may point to those responsible.

References

[1]  F-Secure, "Calculating the Size of the Downadup Outbreak,"  16 January 2009. http://www.f-secure.com/weblog/archives/00001584.html
[2]  J. Hruska, "Time for Forced Updates?  Conficker Botnet makes us Wonder," Arstechnica.com, 02 December 2008. http://arstechnica.com/news.ars/post/20081202-time-for-forced-updates-conficker-botnet-makes- us-wonder.html
[3]  Microsoft Corporation, "Microsoft Security Bulletin MS08-067 - Criticial," 23 October 2008.  http://www.microsoft.com/technet/security/Bulletin/MS08-067.mspx
[4]  P.A. Porras, H. Saidi, and V. Yegneswaran.  "A Multiperspective Analysis of the Storm Worm. SRI Technical Report, 2007.  http://www.cyber-ta.org/pubs/StormWorm/
[5]  H. ren and G.M. Ong, "Exploit MS-08-067 Bundled in Commercial Malware Kit," 14 Nov 2008. http://www.avertlabs.com/research/blog/index.php/2008/11/14/exploit-ms08-067-bundled-in-commercial-malware-kit/
[6]  P. Roberts,  "Sasser Infections Hit Hard, IDG News Services," published in PC World, 2006.  http://www.pcworld.com/article/115979/sasser_infections_hit_hard.html
[8]  C. Williams, "Conficker seizes city's hospital network," The Register (UK), 20 January 2009.
http://www.theregister.co.uk/2009/01/20/sheffield_conficker/
[9]  D. Worthington, "Microsoft: SP2 will not install on pirated copies of XP," 11 May 2004.
http://www.betanews.com/article/Microsoft_SP2_Will_Not_Install_on_Pirated_Copies_of_XP/1084264398
[10]  Patrick Fitzgerald, "Downadup: Geolocation, Fingerprinting and Piracy,"  2009.
https://forums.symantec.com/t5/Malicious-Code/Downadup-Geo-location-Fingerprinting-and-Piracy//ba-p/380993/
[11] Elia Floria, "Downadup: Small Improvements Yield Big Returns," 2008.
https://forums.symantec.com/t5/Malicious-Code/Downadup-Small-Improvements-Yield-Big-Returns//ba-p/381717
[12] Eric Chien, "Downadup: Peer-to-Peer Payload Distribution," 2009.
http://myitforum.com/cs2/blogs/cmosby/archive/2009/01/22/downadup-peer-to-peer-payload-distribution-symantec-security-response-blog.aspx
[13] Joe Stewart, "Rogue Antivirus Dissected," 2008.
http://http://www.secureworks.com/research/threats/rogue-antivirus-part-1/
[14] Paul Baecher and Markus Koetter, "x86 shell code detection and emulation," 2008.
http://libemu.carnivore.it
[15] Jose Nazario, "The Conficker Cabal Announced," Arbor Networks, 12 February 2009.
http://asert.arbornetworks.com/2009/02/the-conficker-cabal-announced/

While the static and dynamic analyses of the Conficker A and B binaries have yielded several insights to its purpose and behavior, attribution of who is responsible for this outbreak remains an open question. Nevertheless, some insights we have gathered may help suggest potential directions one might look pursue in finding the responsible party.

Code Derivation: Our analyses of A and B provide us a degree of confidence in stating that B is a derivative work of A. We have already noted strong similarity in the domain generation algorithm, as well as significant behavioral overlap. In addition, a comparison of the static disassemblies reveals an approximate 35% overlap in the function prototypes used by A and B, which we interpret from experience to indicate a high correlation among the code bases. We also observe a nearly identical binary validation algorithm, with security features, such as key size, improved in version B. B appears to provide protocol enhancements, such as interacting with Internet rendezvous points more patiently than A, perhaps for reliability purposes. B and A also produce nearly identical URL requests to their rendezvous points, except that B has dropped the inclusion of the constant string aq=7. However, diagnosing B as a derivative work of A does not imply that both were created by the same author, only that there is at least some shared relationship among the two development efforts.

One interesting area of difference between A and B is the use of country-based filtering within A, which was excluded in the later release B. Conficker A employs two checks to avoid infecting systems located within the Ukraine. First, it includes a service that determines whether the infection propagation function is about to scan an address that is located in the UA domain. If so, it will select a different IP address to target. Once Conficker A infects a system, it includes a keyboard layout check, via the GetKeyboardLayout API, to determine whether the victim is currently using the Ukrainian keyboard layout. If so, A will exit without infecting the system. This suicide exit scheme has been observed in other malware-related software, such as Baka Software's Antivirus XP Trojan installer [13]. Stewart documents the Baka Software fraudware business in good detail, and notes that the Antivirus XP authors may be excluding their home nation to avoid the attention of local authorities.

Baka Software: Antivirus XP may provide another clue to understanding the purpose of Conficker. After 1 December 2008, Conficker A activates a code segment that attempts to download Antivirus XP from trafficconverter.biz. This site was taken down very early and reports of how effective Conficker A has been in disseminating Antivirus XP are not available. The download code segment for Antivirus XP requires the same digital signature and signature verification routines used to validate binaries from Conficker's Internet rendezvous points. This inclusion of the Antivirus XP download, and the similarities between Conficker's Ukrainian suicide logic and that of the Antivirus XP Trojan installer found in October 2008 suggest a potential relationship between the malware authors and Baka Software. On the other hand, it could also be a potential diversion to associate Conficker with a well-known fraudware product. There is currently no association between Conficker B and Antivirus XP, nor does B include the same Ukraine avoidance logic as A.

Rendezvous Anomaly: Finally, monitoring the Internet rendezvous points of Conficker has yielded a number of groups that are registering Conficker domains for the purposes of census building, and several of these groups interact and collaborate. To date, we are aware of no group that has publicly identified domain registrations or Conficker client connections that it can definitively link to the malware authors. However, on 27 December 2008 we stumbled upon two highly suspicious connection attempts that might link us to the malware authors. Specifically, we observed two Conficker B URL requests sent to a Conficker A Internet rendezvous point:

* * Connection 1: 81.23.XX.XX - Kyivstar.net, Kiev, Ukraine
* * Connection 2: 200.68.XX.XXX - Alternativagratis.com, Buenos Aires, Argentina

Note that these were the only Conficker B requests that were ever sent to Conficker A domains during our entire measurement. The implications of these connections are as follows. The systems that performed these connections employed applications that computed a set of Conficker A domain names. However, these systems employed the Conficker B URL string request, which Conficker A victims are incapable of producing. Furthermore, Conficker B victims include a trigger to prevent connections to any Internet rendezvous points prior to 1 January 2009. This temporal trigger, along with the targeting of a Conficker A domain, indicates that these victims cannot be running B. Thus, these connections must either be associated with a hand-generated request with awareness of variant B's URL format, or a variant application that combined both functions with A and B, i.e., a hybrid test application. The Kiev Ukraine geolocation of connection 1 offers further potential interest because Kiev is also associated as a registered location of Baka Software (baka.kiev.ua).

Conficker B++ has added a new method for remote Win32 binary retrieval and execution. This new method entails the use a named pipe to receiving URLs from remote systems, retrieval of Win32 binaries using this URL, validation that the downloaded executable is properly signed by the Conficker authors, and immediate execution of the binary.

The new Conficker variant adds an extra function to the main thread if the OS is Windows XP, Windows 2000, or Windows 2003 Server as described by the following pseudo-code:

This function creates a named pipe server that allows remote processes as well as local processes to connect to the pipe and communicate information to the Conficker process. The name of the pipe is constructed by the function "create_name_for_pipe", which corresponds to the following code:

The pipe name ("System_7") is passed to the CreateNamedPipe API, which creates a bi-directional pipe where both the server and clients can write and read streams of messages limited to 0x400 bytes. The recurrent choice of constant number 7 here is interesting. Previously, it was used as part of the HTTP rendezvous query in Conficker A and as part of a mutex name. Since the name is not random, any external host or a local process can connect to this pipe and upload a binary. This is easily accomplished through an SMB (TCP/445) connection to the specified pipe. The code repeatedly calls CreateNamedPipe in a loop. If the pipe has been successfully created, then a read from the pipe is attempted. The code reads 0x400 bytes and if the buffer is null-terminated it passes the message to the function "thread_download_file_from_url". The message is interpreted as a string representing a URL that is used to download an executable. This binary is validated using the signature check and RC4 decryption routines before being executed using CreateProcess.

Implications
Overall, the modifications to Conficker B++ appear relatively minor as compared to the significant upgrade in functionality, performance, and reliability, which occurred from Conficker A to B. These smaller and more surgical changes to B appear to address some of the realities that are currently impacting Conficker's binary update strategy. In particular, in Conficker A and B, there appeared only one method to submit Win32 binaries to the digital signature validation path, and ultimately to the CreateProcess API call. This path required the use of the Internet rendezvous point to download the binary through an HTTP transaction. Under Conficker B++, two new paths to binary validation and execution have been introduced to Conficker drones, both of which bypass the use of Internet Rendezvous points: an extension to the netapi32.dll patch and the new named pipe backdoor. These changes suggest a desire by the Conficker's authors to move away from a reliance on Internet rendezvous points to support binary update, and toward a more direct flash approach.

However, Conficker A and B did support through the previous netapi32.dll patch an ability to accept new DLLs, as long as the shell code submitted through the RPC buffer overflow matched the original Conficker infection shell code. This approach was limiting both in the requirement that direct flashing required an easily identifiable shellcode string and a single DLL method loading procedure, both of which are now subject to detection by security software. Conficker B++ dramatically increases the flexibility of the direct flash mechanisms, offering an ability to load digitally signed Win32 executables directly to a Conficker host.

Recently, the Conficker Cabal [15] announced that it has locked all future Conficker A and B domains to prevent their registration and use. Among its impacts, this action effectively prevents blackhat groups associated with Conficker from globally registering future Conficker Internet rendezvous points, preventing them from performing global census or distributing new binary updates to the infected drones (this does not prevent selective DNS poisoning that could be used to target drones within specific zones). However, a new variant of Conficker B has emerged that suggest the malware authors may be seeking new ways to obviate the need for Internet rendezvous points entirely.

Perhaps as one response to the cabal's action, or simply to produce a more efficient push-based updating service, the Conficker authors have released a variant of Conficker B, which significantly upgrades their ability to flash Conficker drones with Win32 binaries from any address on the Internet. Here, we refer to this variant as Conficker B++, as without direct knowledge of these new features added to this binary variant, it will appear to operate and interact with the Internet identically to that of Conficker B. However, as we outline in this section, some subtle improvements in B++, which include the ability to accept and validate remotely submitted URLs and Win32 binaries, could signal a significant shift in the strategies used by Conficker's authors to upload and interact with their drones.

Overview of Variant B++
On Feb 16, 2009, we received a new variant of Conficker. At a quick glance, this variant resembles Conficker B. In particular, it is distributed as a Windows DLL file and is packed similarly. Furthermore, dynamic analysis revealed that this domain generation algorithm was identical to that of Conficker B. Hence, we initially dismissed this as another packaging of Conficker B. However, deeper static analysis revealed some interesting differences. Overall, when we performed a comparative binary logic analysis (see Appendix 2 - Horizontal Malware Analysis) comparing Conficker B with Conficker B++, we obtained a similarity score of 86.4%. In particular, we found that out of 297 subroutines in Conficker B, only 3 were modified in Conficker B++ and around 39 new subroutines were added.

The overall logic restructuring and extensions for Conficker B++ are illustrated in Figure 9. Among the changes observed, we found a restructuring of the main function and introduction of two new paths leading to the CreateProcess API. The first path connects "patch_NetpwPathCanonicalize" to "call_create_process" through "download_file_from_url" and "accept_validated_file". The second path involves the addition of "set_name_pipeserver" which also leads to "download_file_from_url".

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Extensions to Conficker's netapi32.dll Patch

As is common among malware, Conficker incorporates facilities to close the vulnerability that it exploits once it takes ownership of its victim host.  Specifically, Conficker provides an in-memory patch to the RPC vulnerability within the netapi32.dll NetpwPathCanonicalize function.  However, while this patch protects the host from arbitrary RPC buffer overflow, it is specially crafted to allow other Conficker hosts to reinfect the victim, possibly as a second back door
means by which it can install new binary logic into previously infected hosts.  [12].  In Conficker A and B, this pseudo-patch parses incoming RPC requests in search of the standard Conficker shellcode exploit string.   When this string is encountered, the Conficker-infected host will pull the designated DLL binary payload from the remote attacker, as specified in the URL embedded within the shellcode.   The DLL is loaded using the svchost command, as specified in the shellcode.   This process is illustrated in the top panel of Figure 10.

Conficker B++ now extends and simplifies the buffer overflow, allowing a remote agent to provide a URL reference to a digitally signed Win32 exectuable.   This Win32 executable is pulled by the Conficker B++ host, its digital signature is validated or rejected (see Binary Download and Validation),  and if acceptable the Win32 binary is then directly spawned by the CreateProcess routine.   This modification is shown in the
bottom panel of Figure 10.    Conficker B++ is no longer limited to reinfection by similarly structured Conficker DLLs, but can now be pushed new self-contained Win32 applications. These executables can infiltrate the host using methods that are not detected by the latest anti-Conficker security applications. 

While Conficker A singularly relies on exploiting the MS08-067 vulnerability for its propagation, Conficker B is more versatile and implements two additional strategies to embed itself into additional hosts.  Here, we describe the three strategies:

MS08-67 Propagation: Conficker propagates by exploiting the MS08-67 vulnerability in the Microsoft Windows server service.  An anonymized packet-level summary of a typical Conficker exploit is shown in Figure 6.  The remote attacking host begins by negotiating SMB (server message block) protocol and initiating an SMB session on port 445/TCP of the victim.  The attacking host binds to the SRVSVC pipe and proceeds to issue the NetPathCanonicalize request, which has the exploit payload embedded. The embedded shell code coerces the victim host to contact the attacking host on a connect-back port and download a PE (portable executable) DLL file.  The shell code also issues Windows API calls to ensure that the DLL is executed as a service through svchost.exe.

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The content of the exploit packet varies even across repeated infection attempts by the same host.  So a naive analysis of payload content is insufficient to distinguish between variants of Conficker.  We used the sctool utility in Libemu [14] (a library of tools to build emulators) to explore exploit traces in greater detail.  We provide a summary of the Libemu shellcode output for Conficker A and B in Figure 7.  

The URL reference in bold highlights the common method for pulling in the Conficker dll binary from the application port provided by the Conficker client.

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The output shows the embedded url download request in the shell code and confirms that both Conficker A and Conficker B use a similar connect-back mechanism to upload the binary.  Interestingly, we also find that the libemu stepcounts are useful in differentiating between the shellcode produced by Conficker A and B.  We compare the shellcode of all hosts contacting the SRI honeynet and classify them as A/B based on intelligence gathered separately from rendezvous point monitoring.  We find Conficker A's shellcode stepcounts range between 84195 and 84231 while Conficker B's shellcode stepcounts range between 85047 and 85083, as shown in Figure 8. There was one Conficker A host that was misclassified by our rendezvous point analysis as a Conficker B host.  Based on Libemu's analysis we can confirm that the host was a Conficker A host
when it contacted our honeynet (suggesting the IP address was probably a NAT or DHCP).

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NetBIOS Share Propagation: 
Conficker B exploits weak security controls in enterprises and home networks to find additional vulnerable machines through open network shares and brute force password attempts using a list of over 240 common passwords.  In particular, it copies itself to the admin share or the IPC (interprocess communication) share launched using rundll32.exe. 
We believe that this and the USB (universal serial bus) propagation vector described below (which are both unique to Conficker B) might have largely contributed to its impressive proliferation.

USB Propagation: 
Finally, Conficker B copies itself as the autorun.inf to removable media drives in the system, thereby forcing the executable to be launched every time a removable drive is inserted into a system.  It combines this with a unique social-engineering attack to great effect.  It sets the "shell execute'' keyword in the autorun.inf file to be the string "Open folder to view files'", thereby tricking users into running the autorun program.  

Both Conficker A and B query the list of random domains generated for any available files to be downloaded. The list of domains is queried every 3 hours starting on 26 November 2008 for version A and every 2 hours starting on January 1, 2009 for version B.  The worm first tries to resolve the domain name to an IP address. If that succeeds, it proceeds by sending an HTTP request in the form of a string

• * http://domainname/search?q=n\&aq=7} (for Conficker A)
• * http://domainname/search?q=n} (for Conficker B)

The second argument (aq=7) used by Conficker A is always a constant.  We speculate that this might have been meant to be a version identifier, which has since been dropped by Conficker B.  The number 7 also appears in the mutex string  "Global\m-7'', where "m" is a number generated based on the name of the infected computer. The value of q is read from a global variable that the worm's code initializes first to 0.
This value is also stored in the registry under the key name

• SOFTWARE\Microsoft\Windows\CurrentVersion\Nls

in Conficker A. Based on static analysis, we find that this value is incremented and saved in the registry every time the infected machine successfully infects another machine. When the machine is rebooted, the value of qis read from the registry so that the value used in the HTTP request indicates the total number of computers that the given machine successfully infected since it has been infected.

The URL is opened and the Windows API InternetReadFile is invoked to read all the available data the queried server sends back.

Conficker reads and saves the data into memory for further analysis.
First, it checks if the downloaded data (or file) has more than 128 bytes for version A and 512 bytes for version B. The reason for these checks becomes apparent when statically analyzing the code that is executed after these checks. Figure 5 illustrates how Conficker extracts from the downloaded file a digital signature to check if the downloaded file is properly signed, and then decrypts the file contents before executing it. This effectively prevents would-be hijackers with advanced knowledge of the domain names from registering and uploading their own binaries to the Conficker drones.

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From the decryption and signature check that Conficker uses, we conclude that Conficker employs two encryption schema to maintain control over its drones.  It uses RC4 stream cipher and a 512-bit key as a fast way to decrypt the file downloaded from a queried server.
However, it will do so only if the downloaded file has been digitally signed using a public key scheme with a 4096-bit key. The signature check is done by computing a hash of the payload and by using an embedded exponent and modulus.

As described above, Conficker A builds a candidate list of 250 Internet rendezvous points (i.e., domains) seeded by the current UTC date.  Figure 3 illustrates our dissection
of the subroutine that implements domain generation logic.  The first two blocks of this subroutine randomly generate strings of 5 to 11 lower case alphabets.  We discovered that Conficker implements its own random number generator, which we annotate as subgenerate_random().  It selectively chooses between this function and the system rand()function.
The former is seeded with GMT and is deterministic, while the latter introduces non-determinism.  In block loc_9A995D,it determines the length of the domain prefix by adding 8 to a random value between -3 and 3.  In loc_9a9989,generate_random() is repeatedly called to generate a positive integer between 0 and 25.  This is added to `a' producing a random lower case alphabet that is used to construct the domain prefix. A top-level domain (TLD) suffix chosen randomly between .com, .net, .org, .info, and .biz is then appended to the domain name. The outer loop builds 250 domain names and creates threads to perform name resolutions on these domains. Conficker B's domain generation algorithm is similar but also includes additional TLD suffixes (.ws, .cn, .cc).

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Figure 3: Conficker A/B Rendezvous Protocol

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Random Number Generation: We will now describe the random number generation process employed by Conficker A that is used as part of the rendezvous point generation algorithm.  We begin by describing subroutine query_search_engines_set_time(),which is annotated in Figure 4
.  The first block uses rand() to randomly select from one of six search engines (w3.org, ask.com,msn.com, yahoo.com, google.com and baidu.com).  It then invokes subroutine get_date_from_url(),which generates an HTTP GET request to obtain the time from the remote webserver.  This subroutine further invokes subroutines fetch_date_from_url() and parse_date_from_url(). 

The former uses the Windows API call HttpQueryInfoA with info-level HTTP_QUERY_DATE to obtain the date field of the HTTP header.  The latter subroutine simply parses the date string GMT returned by the former.  As the query returns only the day, month, and year values, repeated queries on the same day would yield the same result.

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loc_9A995D:
push 20h
push 40h
call dword_9A10C0      ; GlobalAlloc(0x40, 0x20) - alloc 32by
mov edi, eax      ; edi = GlobalAlloc() = domain
mov [ebp+ebx*4+var_454], edi
call sub_9A96EE      ; eax = generate_random()
push 4
cdq       ; sign extends word in eax
pop ecx       ; ecx = 4
idiv ecx       ; div eax by ecx, remainder in edx
mov [ebp+var_4], 0       ; var_4 = 0
mov esi, edx
add esi, 8       ; esi = edx + 8 (edx -3 to 3)
jz short loc_9A99AC

loc_9A9989:
call sub_9A96EE       ; eax = generate_random()
push eax
call sub_9B3330       ; eax = abs(random_num)
pop ecx
cdq       ; edx = 0
push 1Ah
pop ecx       ; ecx = 26
idiv ecx       ; div eax by ecx, remainder in edx
mov eax, [ebp+var_4]       ; eax = var4
add dl, 61h       ; dl = dl + 'a'
inc [ebp+var_4]       ; var4++
cmp [ebp+var_4], esi
mov [eax+edi], dl       ; edi[var4] = dl
jb short loc_9A9989       ; if var4 < esi jmp to 9a9989

loc_9A99AC:
mov byte ptr [edi+esi], 0
call sub_9A96EE       ; generate_random()
push 5
pop ecx       ; set ecx = 5
xor edx, edx       ; set edx = 0
div ecx       ; edx = eax % 5
push off_9B53A8[edx*4]       ; suffix= .com,.net,.org,.info,.biz}
push edi
call sub_9B3336       ; strcat(domain, suffix)
inc ebx       ; ebx = ebx + 1
cmp ebx, 0FAh
pop ecx
pop ecx
jl short loc_9A995D       ; check if ebx < 250
mov [ebp+var_8], 1       ; var_8 = 1

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The value returned by get_date_from_urlis used to compute lpsystemtime (i.e., number of 100-nanosecond intervals since 1601).  This is divided by 0x58028e44000 (number of nanoseconds in a week), multiplied by 0x464da5676 and added to 0xb46a7637 (the final two constants are replaced by 0x352c94565 and 0xa3596526 in Conficker B).  The final sum is stored in a special memory location, dword 0x9b53c0.  This value is used to seed the generate_random()subroutine.  The generate_random()functions are essentially identical except that A uses a constant value of 0x64236735 in its floating point computation, which is replaced by 0x53125624 in Conficker B.

Among the key functions of Conficker is that of probing the daily set of Internet rendezvous points for a new Windows executable file to download and execute.  This mechanism provides an effective binary updating service similar to that of other traditional botnets, with the exception that the Conficker update service is highly mobile and its location (i.e., to date we have not confirmed this feature in use by the malware authors) is recomputed each day by all infected clients.    Although many groups have been able to break the domain generation algorithm and  registered rendezvous points, Conficker's authors have taken care to ensure that other groups cannot upload arbitrary binaries to its infected drones.

Both Conficker A and B clients incorporate a binary validation mechanism to ensure that a downloaded binary has been signed by the Conficker authors. 
Figure 2 illustrates the download validation procedure used to verify the authenticity of binaries pulled from Internet rendezvous points.
The procedure begins with Conficker's authors computing a 512-bit hash M of the Windows binary that will be downloaded to the client.  The binary is then encrypted using the symmetric stream cipher RC4 algorithm with password M.
Next, the authors compute a digital signature using an RSA encryption scheme, as follows:  M^epriv mod N = Sig,  where N is a public modulus that is embedded in all Conficker client binaries.   Sig is then appended to the encrypted binary, and together they can be pushed to all infected Conficker clients that connect to the appropriate rendezvous point.  

Figure 2: Conficker Downloaded Binary Validation

Once received, the client removes the digital signature and recovers M using N and the public exponent epub,which is also embedded in the Conficker client binary.  M is recovered as follows:  M = Sig^epub mod N.   

The client then decrypts the binary using password M, and confirms its integrity by comparing its hash to M(i.e., the hash value originally computed by the Conficker authors).  If the hash integrity check succeeds, the binary is then stored and executed via Windows shellexec(). 
Otherwise the binary is discarded.  Both A and B use equivalent hash and encryption protocols, with the exception that B uses an expanded 4092-bit modulus, whereas A employed a 1024-bit modules.  The public exponent epub and module N values from the Conficker A and B binaries is shown in Table 1.

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Conficker A Embedded Keys

Conficker B Embedded Keys

epub = 1B16A Modulus: size = 64 words  =1024 bits 617BF0CF E816D789 31ED091B E72EFE45 56B9248A 364173F6 5037EF78 CA86ECDF 4B96E24F 50F4E6C3 E85616BA 5BF2764E 98574572 970B077A ABE91715 56136DF6 551A66DE 949EAEAE 2560EE53 CB01FC34 F41D66F7 6F1DE9B0 821BA9E9 6E5CA3C1 6561DAE3 6A36AB28 EEE93EA5 E23AC10A 1EF64327 3C2A030B E9FE919B 25BF7640

epub = 0C351 Modulus: size = 256 words   = 4094 bits F52DA7E7 4912CA45 D61E44E6BA1B4C72 8BF0723C F375EB4B CD44E85E 21E95687 333406E6 42934976 3603E8EC 4DADA619 967F5912 25418501 7E83E2CB B385DF72 FB59E1DD 2D9A7897 E93DB6B2 39455258 9FC8901B 422B5CD7 D86AA6DE 4CF2D003 2E2472AF 4DF38C9D F24D2F2F 2989D649 FFC6C9A2 B6985FF2 92AD0968 10D57010 B6DA1CEA CC03D4BC 578E9E8D BCFCCF8C 319EC35B 8A08DA5B BF802693 8045DBD2 AF873383 5FF6C269 14349915 CC880FCB 93E92944 F97E9E45 938A8712 BB43338E 605B400C 3140864C 13659917 8AC26CE4 D930A4E5 BB6AD6F3 02DADFEB 7E386DEC 6811EE23 A87D628A C69E9393 23F17BDC 3972665D 56E53DC8 A8D920C3 E435259A 7ED4993B 74D7D161 EB6AE350 3D315A49 4A29DE21 D1FC30CD 7398D7FD 53A64B60 EEF95D08 9721E605 D6B7D9ED B13400BC 26BD6B76 1C2C8A60 2D58E6B6 09404D47 9DB1835B A28E983C 7A5D9E2D C80DF107 B047261B 08701C1A 9CC24C76 0EF33ACF A800C61E 9247CB15 07F91D7E 4992AA42 ED7104DC E6DCE7D6 25BD3CAD ECFA3218 FBA5B7FA 5249A1CC A76030BA 95A3B0D3 61DAF2E5 97D227BD 3366D8C0 D2130437 CB3F9D36 2E6B7924 0BE12269 485BC1AD 00D5E18A 06443787 744CAEF5 A30F204B D4086357 3AF0EB57 C4031AE3 2D179ADF 441FFD7F B749DA71 B5263FBA CAFE9CDD ECDB7018 96846399 4C801030 BC4D7333 2C79C3B2 41CD6883 7DED455C 88A8BEE7

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Like most malware, Conficker propagates itself in the form of a packed binary file.  Our first step in analyzing Conficker consists of undoing the work of the packers and obfuscators to recover the original malware binary code. Conficker is propagated as a dynamically linked library (DLL), which has been packed using the UPX packer.
The DLL is then run as part of svchost.exe and is set to automatically run every time the infected computer is started.  After unpacking, we find that the UPX packed binary file is not the original code but incorporates an additional layer of packing. We use IDA Pro to remove this second layer of obfuscation and dump the original code from memory. To do so, we first run the Conficker service, snapshot the core Conficker library as a memory image, and from this code segment reconstruct a complete Windows executable program. The program requires a PE-header template, and we compute an entry point that allows the program to enter Conficker'scode segment. 

This appears to be a clever way of making the analysis of Conficker a bit more challenging than usual.  We now
describe the static analysis of the original code, which reveals the full extent of the malware logic and capabilities.

Conficker A/B Top-Level Control Flow

Figure 1  illustrates a flow diagram of the main thread for both variants of the Conficker agent, A and B. In both cases, the Conficker agent is distributed and run as a dynamically linked library. Its base code has been compiled as a DLL and its DLLMain function initiates the main thread represented by the diagram. The agent code proceeds by first checking the Windows version, and based on this result creates a remote thread in processes such as svchost.exe. This is done by invoking LoadLibrary, where the copy of the DLL is passed as an argument. The malicious library then copies itself in the system root directory under a random file name. After initiating the use of Winsock DLL, the bulk of the malicious code logic is executed.

Figure 1: Conficker A (left) /B (right): Top-level control flow

Conficker A's agent proceeds as follows. First, it checks for the presence of a firewall. If a firewall exists, the agent sends a UPNP message to open a local random high-order port (i.e., it asks the firewall to open its backdoor port to the Internet). Next, it opens the same high-order port on its local host: its binary upload backdoor. This backdoor is used during propagation, to allow newly infected victims to retrieve the Conficker binary. It proceeds to one of the following sites to obtain its external-facing IP address www.getmyip.org, getmyip.co.uk, and checkip.dyndns.org, and attempts to download the GeoIP database from maxmind.com. It randomly generates IP addresses to search for additional victims, filtering Ukraine IPs based on the GeoIP database. The GeoIP information is also used as part of MS08-67 exploit process [10]. Conficker A then sleeps for 30 minutes before starting a thread that attempts to contact http://trafficconverter.biz/4vir/antispyware/ to download a file called loadadv.exe. This thread cycles every 5 minutes.

Next, Conficker A enters an infinite loop, within which it generates a list of 250 domain names (rendezvous points). The name-generation function is based on a randomizing function that it seeds with the current UTC system date. The same list of 250 names is generated every 3 hours, i.e., 8 times per day. All Conficker clients, with system clocks that are at minimum synchronized to the current UTC date, will compute and attempt to contact the same set of domains. When contacting a domain for which a valid IP address has been registered, Conficker clients send a URL request to TCP port 80 of the target IP, and if a Windows binary is returned, it will be validated via a locally stored public key, stored on the victim host, and executed. If the computer is not connected to the Internet, then the malicious code will check for connectivity every 60 seconds. When the computer is connected, Conficker A will execute the domain name generation subroutine, contacting every registered domain in the current 250-name set to inquire if an executable is available for download.

Conficker B is a rewrite of Conficker A with the following noticeable differences. First, Conficker A incorporates a Ukraine-avoidance routine that causes the process to suicide if the keyboard language layout has been set to Ukrainian. Conficker B does not include this keyboard check. B also uses different mutex strings and patches a number of Windows APIs, and attempts to disable its victim's local security defenses by terminating the execution of a predefined set of antivirus products it finds on the machine. It has significantly more suicide logic embedded in its code, and employs anti-debugging features to avoid reverse engineering attempts.

Conficker B uses a different set of sites to query its external-facing IP address www.getmyip.org, www.whatsmyipaddress.com, www.whatismyip.org, checkip.dyndns.org. It does not download the fraudware Antivirus XP software that version A attempts to download. Conficker's propagation methods vary among A and B and are described in Section Conficker Propagation. Furthermore, a recent analysis by Symantec has uncovered that the GeoIP file is directly embedded in the Conficker B binary as a compressed RAR (Roshal archive) file encrypted using RC4 [11].

Like Conficker A, after a relatively short initialization phase followed by a scan and infect stage, Conficker B proceeds to generate a daily list of domains to probe for the download of an additional payload. Conficker B builds its candidate set of rendezvous points every 2 hours, using a similar algorithm. But it uses different seeds and also appends three additional top-level domains. The result is that the daily domain lists generated by A and B do not overlap.

Introduction

Conficker is one of a new interesting breed of self-updating worms that has drawn much attention recently from those who track malware. In fact, if you have been operating Internet honeynets recently, Conficker has been one very difficult malware to avoid. In the last few months this worm has relentlessly pushed all other infection agents out of the way, as it has infiltrated nearly every Windows 2K and XP honeypot that we have placed out on the Internet. From late November through December 2008 we recorded more than 13,000 Conficker infections within our honeynet, and surveyed more than 1.5 million infected IP addresses from 206 countries.

More recently, our cumulative census of Conficker.A indicates that it has affected more than 4.7 million IP addresses, while its successor, Conficker.B, has affected 6.7M IP addresses (see SRI Appendix I: Conficker Census). Our analysis finds that the two worms are comparable in size (within a factor of 3) and the active infection size of Conficker A and B are under 1M and 3M hosts, respectively. The numbers reported in the press are most likely overestimates. That said, as scan and infect worms go, we have not seen such a dominating infection outbreak since Sasser [6] in 2004. Nor have we seen such a broad spectrum of antivirus tools do such a consistently poor job at detecting malware binary variants since the Storm [4] outbreak of 2007.

Early accounts of the exploit used by Conficker arose in September of 2009. Chinese hackers were reportedly the first to produce a commercial package to sell this exploit (for $37.80) [5]. The exploit employs a specially crafted remote procedure call (RPC) over port 445/TCP, which can cause Windows 2000, XP, 2003 servers, and Vista to execute an arbitrary code segment without authentication. The exploit can affect systems with firewalls enabled, but which operate with print and file sharing enabled. The patch for this exploit was released by Microsoft on October 23 2008 [3], and those Windows PCs that receive automated security updates have not been vulnerable to this exploit. Nevertheless, nearly a month later, in mid-November, Conficker would utilize this exploit to scan and infect millions of unpatched PCs worldwide.

Why Conficker has been able to proliferate so widely may be an interesting testament to the stubbornness of some PC users to avoid staying current with the latest Microsoft security patches [2]. Some reports, such as the case of the Conficker outbreak within Sheffield Hospital's operating ward, suggest that even security-conscious environments may elect to forgo automated software patching, choosing to trade off vulnerability exposure for some perceived notion of platform stability [8]. On the other hand, the density of where the vast bulk of Conficker victims are concentrated may also suggest other reasons, such as the wide use of unregistered (pirated) Windows releases, which Microsoft does not patch [9].

In this paper, we crack open the Conficker A and B binaries, and analyze many aspects of their internal logic. Some important aspects of this logic include its mechanisms for computing a daily list of new domains, a function that in both Conficker variants, laid dormant during their early propagation stages until November 26 and January 1, respectively. Conficker drones use these daily computed domain names to seek out Internet rendezvous points that may be established by the malware authors whenever they wish to census their drones or upload new binary payloads to them. This binary update service essentially replaces the classic command and control functions that allow botnets to operate as a collective. It also provides us with a unique means to measure the prevalence and impact of Conficker A and B. The contributions of this paper include the following:

A static analysis of Conficker A and B. We dissect its top level control flow, capabilities, and timers.
A description of the domain generation algorithm and the rendezvous protocol.
An empirical analysis of infected hosts observed through honeynets and rendezvous points.
Exploration of Conficker's Ukrainian evidence trail.
A first look at a variant of Conficker B (which we call B++) and the implications of its binary flash mechanism.

Ripear con el metodo de las 3 pasadas

Este metodo se explica en de todas formas lo hace partiendo de los *.vob ya en el disco duro, se puede hacer directamente de este modo:

Primero el sonido:

mencoder -dvd 1 -ovc frameno -o frameno.avi -oac mp3lame -lameopts abr:br=128

Primera pasada:
mencoder -dvd 1 -nosound -oac copy -o /dev/null -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=800:vhq:vpass=1:vqmin=1:vqmax=31 -vop scale -zoom -xy 640 -npp lb


Segunda pasada:

Podemos hacerlo de dos formas, directamente al avi, o mediante "three pass encoding", o lo que es lo mismo"en 3 pasadas".

Como ya me he sacado de la manga una Autoridad Certificadora ya puedo generar mi propio certificado.

Genero mi clave privada del futuro certificado digital :

openssl genrsa -des3 -out www_privada.pem -passout pass:miclavepreferida 2048

Ole, ya tengo mi clave de servidor privada con cifrado 3DES de 2048 bytes.

Ahora hago la petición de certificado donde genero el propietario y emisor del mismo :