Microsoft Windows RPC Vulnerability MS08-067 (CVE-2008-4250) FAQ – October 2008 [UPDATED]

This is Frequently Asked Questions document about new, recently patched RPC vulnerability in Microsoft Windows. The document describes related Trojan and worm malware as well.
It is worth of noticing that code execution type vulnerabilities in Office programs are widely used to industrial espionage since 2006. This time the exploitation represents the use of non-Office vulnerabilities and e-mail attack vector is not used.

Update: After the weekend the malware analyses shows that the Trojan has designed to steal credential information and to collect a botnet-like network.

Q: What is the recent Microsoft Window RPC vulnerability disclosed in October?
A: This vulnerability is caused by an error when processing malformed RPC (Remote Procedure Call) requests. The issue was disclosed by the vendor after active exploitation of the vulnerability.
Q: How does the vulnerability mentioned works?
A: The vulnerability is code execution type vulnerability. Attacker successfully exploiting this vulnerability can run code of his or hers choice in the affected machine.
This vulnerability is caused due to overflow when handling malformed RPC requests. This enables executing arbitrary code of the attacker. Technically the vulnerability exists in the Server service.

Q: When this vulnerability was found?
A: The exact information is not available. Information about upcoming security update was announced on 22nd October, but this vulnerability has been used in targeted attacks at least two weeks already. The exploitation disclosed the existence of vulnerability.

Q: What is the mechanism in exploitation?
A: Information was not disclosed, but during the exploitation malicious executables are being downloaded and executed from the remote Web site.

Q: Is the exploit code of this vulnerability publicly released?
A: Yes. On Friday 24th October the proof of concept code was released on a blog of security researcher and on public, moderated security mailing list. The PoC has been released at several well-known exploit and security community Web sites too. Metasploit module has been released too (link). PoC’s work against Windows XP SP2, Windows XP SP3 and Windows 2003 Server SP2 machines.

Q: Which Windows versions are affected?
A: Microsoft Windows 2000, Windows XP, Windows Vista, Windows 2003 Server and Windows Server 2008 systems are affected.

Q: I am using the 7 Pre-Beta version of Windows, is my operating system affected?
A: According to the Microsoft it is affected too. An update is available (see MS08-067).

Q: I am a home user, is it possible to update my system in a normal way via Microsoft Update?
A: Yes, visiting the Microsoft Update Web site at will update the system against the exploitation of the vulnerability. If the Automatic Updates is enabled the system will be updated automatically without user’s actions.

Q: Where are the official Microsoft documents related to this case located?
A: The official Security Bulletin MS08-067, entitled Vulnerability in Server Service Could Allow Remote Code Execution (958644) has been released at Microsoft TechNet Security section:
Updated information released by the vendor has been covered at MSRC Blog (The Microsoft Security Response Center Blog). The address of the blog is
File information of the MS08-067 security update has been released at separate Knowledge Base document #958644:
Microsoft Security Advisory #958963 released to notify the availability of the security update is located at

Q: What the term ‘out-of-band’ means?
A: Normally Microsoft releases security updates once a month, at the second Tuesday of the every month. Very rarely, during the Windows ANI vulnerability etc. the security update will come out outside of this regular update cycle. Out-of-band and out-of-cycle describe the situation when waiting the regular update Tuesday, so-called Patch Tuesday is not enough to protect Windows systems against exploitation.
The next security updates will be released on Tuesday 11th November.

Q: Is this a new Slammer worm?
A: No, due to new security features included to SP2 etc. However, on 3rd Nov it was reported about the worm exploiting this vulnerability.

Q: Are there any workarounds available? Our organization is making tests with the patch still.
A: The security bulletin lists the following workarounds:
-Disable the Server and Computer Browser services
-Block TCP ports 139 and 445 at the firewall

Q: Is there Snort rules for this vulnerability available?
A: Yes. Additional details can be obtained at
known as a ruleset against Microsoft DCE/RPC remote code execution attempts.
The download address is
(to paying Sourcefire customers)
Emerging Threats project has released new signatures too, details at

Q: What is the situation of Nessus plugins related to this vulnerability?
A: Nessus Plugin ID #34476 has been released. More information is available at

Q: What are the target organizations etc. of this vulnerability?
A: This information is not available and probably it will never go public. Microsoft has confirmed that fever than 100 organizations are targeted in targeted attacks.

Q: Is there information about file sizes used during the attacks?
A: Yes. The size is 397,312 bytes.
Update: The size can be anything between 49,152 and 417,792 bytes.

Q: How the user can notify the infection?
A: It is reported that the command prompt will appear.

Q: What are the names of malwares exploiting this vulnerability?
A: There are reports about a data collecting Trojan (Gimmiv.A) and a Trojan searching for non-patched machines on LAN (Arpoc.A).

The following names are being used (listed in alphabetical order):
AhnLab – Dropper/Gimmiv.397312 since 2008.10.24.04
Authentium – W32/Gimmiv.A since 23rd Oct
Avira – TR/Dldr.Agent.gcx since 24th Oct, iVDF
Bitdefender – Win32.Worm.Gimmiv.A since since 23rd Oct
- dropper detected as Win32.Worm.Gimmiv.B
CA – Win32/Gimmiv.A since eTrust 31.6.6167
ClamAV – Trojan.Gimmiv since 8524
- Trojan.Gimmiv-1…Trojan.Gimmiv-7 since 8526
Dr.Web – DLOADER.PWS.Trojan since 23rd Oct
Eset – Win32/Gimmiv.A since 24th Oct, v.3551
- Win32/Spy.Gimmiv, Win32/Spy.Gimmiv.A since v.3553
- Win32/Spy.Gimmiv.B since v.3555
Fortinet – W32/Gimmiv.A!tr.spy
- name change: W32/Gimmiv.A!worm since 9.676
F-Secure – Trojan-Spy:W32/Gimmiv.A since 2008-10-24_01
- Trojan-Spy:W32/Gimmiv.B since 2008-10-24_05
- Trojan-Spy:W32/Gimmiv.C, D, E, F variants since 2008-10-24_08
- Net-Worm.Win32.Gimmiv.a since 25th Oct 2008-10-25_01
McAfee – PWS.y!C91DA1B9 since DAT5413
- Spy-Agent.da since 23rd Oct, DAT5414, its DLL component detected as Spy-Agent.da.dll
Microsoft – TrojanSpy:Win32/Gimmiv.A[.dll] since 23rd Oct
- since 24th Oct update 1.4005 included signatures
- exploit: Exploit:Win32/MS08067.gen!A
Kaspersky – Trojan-Downloader.Win32.Agent.alce since 24th Oct,
Panda Security – detected as ‘Suspicious file’ since 23rd Oct,
- Gimmiv.A since 24th Oct
PCTools – Trojan-Spy.Gimmiv.A
Prevx – detected as ‘Cloaked Malware‘
Rising – Trojan.Spy.Win32.Undef.z since 23rd Oct,
Sophos – Sus/Dropper-A since 21st Aug (based to heuristic techniques)
- additionally Troj/Gimmiv-A, IDEs since 4.34.0,
- Troj/Gimmiv-Gen since 4th Nov
Symantec – Infostealer since 23rd Oct
- name change: Trojan.Gimmiv.A since 24th Oct, rev. 024
- malicious files detected as Bloodhound.Exploit.212
Trend Micro – WORM_GIMMIV.A since 5.617.00
- TSPY_GIMMIV.A since 5.617.00

where ’2008.10.24.04’ states that these virus signatures or newer include a protection for the malware.

Alias names CVE-2008-4250, W32.Slugin.A and W32/NetAPI32.RPC!exploit.M20084250 are in use too.

Update: Added Arpoc section:
BitDefender – Win32.Worm.Gimmiv.B
CA – Win32/Gimmiv.B since 31.6.6172
Dr.Web – Win32.HLLW.Jimmy.3 since unknown signatures
McAfee – Spy-Agent.da since DAT5414, its DLL component detected as Spy-Agent.da.dll

Update: Added RPC worm section:
AntiVir – TR/Expl.MS08-067.G
BitDefender – Trojan.Downloader.Shelcod.A
ClamAV – Exploit.MS08-067 since 8566
Eset – Win32/Exploit.MS08-067.B, C and D since 3576
F-Secure – worm component as Exploit.Win32.MS08-067.g
- kernel component as Rootkit.Win32.KernelBot.dg
Ikarus – Virus.Exploit.Win32.MS08.067.g
Kaspersky – Exploit.Win32.MS08-067.g since 31th Oct
McAfee – kernel component as KerBot!37E73FFB since DAT5422
Microsoft – Exploit:Win32/MS08067.gen!A
- Trojan:Win32/Wecorl.A
- Trojan:Win32/Wecorl.B
Norman – kernel component as w32/agent.jbvo
Prevx – Worm.KernelBot
Sophos – Mal/Generic-A
- Exp/MS08067-A since 4th Nov
Symantec – W32.Wecorl since 3rd Nov (latest daily certified version) rev. 052
- W32.Kernelbot.A since 3rd Nov (latest daily certified version) rev. 041
Trend Micro – WORM_KERBOT.A since 5.637.00
- WORM_WECORL.A since 5.640.05

Q: What kind of payload this Trojan horse has?
A: This is what the Trojan gathers (according to Microsoft’s document):
*User Name
*Computer Name
*Network Adapters / IP Addresses
*Installed com objects
*Installed programs and installed patches
*Recently opened documents
*Outlook Express and MSN Messenger credentials
*Protected Storage credentials

Q: What kind of Trojan has attacked to the targeted organizations?
A: It is a very sophisticated and dangerous Trojan. It encrypts the data with AES and deletes itself after its operations. Before sending the gathered data to the attacker it reports the AV software of the installation (from HKEY_LOCAL_MACHINE\SOFTWARE\) as a parameter (BitDefender, Jiangmin, Kingsoft, Kaspersky, Microsoft OneCare, Rising and Trend Micro).

Q: Are there any changes to Windows registry or the file system made by this malware?
A: The following registry key is being modified:
The display name of the service being generated is System Maintenance Service.
The malicious files are being copied to System32\wbem folder including basesvc.dll, syicon.dll, winbase.dll and winbaseInst.exe. NOTE: After being executed the Trojan deletes these files and itself.
Update: According to Arbor Networks the file C:\Documents and Settings\LocalService\Local Settings\Temporary Internet Files\macnabi.log is being dropped too.

Q: Now I know that my anti-virus software can report computers in my organizations as clean because the Trojan has deleted itself from the system. What are the malicious executables that I can search them and examine logs etc.?
A: There are several names and all of the files has same size mentioned earlier, i.e. 397,312 bytes.
Update: According to McAfee the size varies from 49,152 to 417,792 bytes.

The most common file name is N2.exe. However, file names Nx.exe are widely spreading as well; [x] represents a number from 1 through 9.
The MD5 hash of the one specific N2.exe file in the wild on 23rd Oct is f173007fbd8e2190af3be7837acd70a4.
Update: To list one more the MD5 hash of n5.exe is 24cd978da62cff8370b83c26e134ff4c.

Prevx database knows the following file names too:
15197927.EXE, 00003106.EXE, NVIR/N2.EXE, 18912604.EXE, 54800477.DAT
The format of the file can be NVIR/N3.EXE etc. too.

Q: What type of network connections these malware make?
A: Gimmiv.A sends an ICMP Echo Request packet to multiple IP addresses including the string ”abcde12345fghij6789”.

Q: How can I recognize malicious files spreading RPC worm (Exploit.Win32.MS08-067.g)?
A: The files names reported in the wild are 6767.exe and KernekDbg.exe.

Q: What is the size of these files?
A: The size are various, but many of them are 16,384 bytes long.

Q: What kind of network connections the worm makes and are there any modifications made to Windows registry?
A: It connects to,, and Yes, the worm will add the new value to HKLM\SOFTWARE\Licenses and HKLM\SOFTWARE\Google.

Q: Are there any changes to Windows HOSTS file?
A: Yes, the lines
will be added yo the HOSTS file.

Q: Is there CVE name available to this issue?
A: Yes. The Common Vulnerabilities and Exposures project ( has released the following CVE candidate CVE-2008-4250:

Q: What is the CVSS severity of this vulnerability?
A: The CVSS (Common Vulnerability Scoring System) score is 10.0 (High).

Q: Is there a CWE class assigned?
A: The CWE (Common Weakness Enumeration) ID of the vulnerability, in turn, is #119, i.e. Failure to Constrain Operations within the Bounds of an Allocated Memory Buffer class:

Q: Is there a CME name available?
A: No. The Common Malware Enumeration (CME) project has not assigned an identifier for these malware.

Q: When exploiting this RPC vulnerability is the authentication needed?
A: On Windows 2000, XP, and Windows Server 2003 systems arbitrary code can be run without authentication. On Vista systems the authentication is needed.

Q: What is the vulnerable component?
A: It is netapi32.dll (Net Win32 API DLL). On Windows 2000 SP4 the non-affected version is 5.0.2195.7203, on Windows XP SP3 5.1.2600.5694 and on Vista SP1 there are several 6.0.6000.xxxx versions, see KB958644 for details. The vulnerable Windows API call is NetPathCanonicalize(), in turn.
Secunia has renamed its vulnerability advisory to Windows Path canonicalisation vulnerability. It states that processing directory traversal character sequences in path names enables to send drafted RPC requests to the Server Service.

(c) Juha-Matti Laurio, Finland (UTC +2hrs)
The author has released several Microsoft Office 0-day vulnerability FAQ documents, e.g.
and Windows Vector Markup Language vulnerability FAQ’s
since 2006.

Revision History:
1.0 25-10-2008 Initial release
1.1 26-10-2008 Updated document and some minor fixes
1.2 26-10-2008 Major updates to Trojan section, added credits, information of non-affected dll versions and Snort rule reference
1.3 27-10-2008 Added information about the various file names and sizes, a separate Arpoc section and Nessus plugin reference and [UPDATED] to the title
1.4 27-10-2008 Several virus description release dates and ID’s added, updated the summary to clarify the characteristics of the exploitation
1.5 28-10-2008 Added Microsoft Security Advisory #958963 link
1.6 29-10-2008 Added names to Arpoc Trojan section
1.7 03-11-2008 Updated the exploit/PoC section and added information about the worm exploiting the vulnerability
1.8 04-11-2008 Added names to RPC worm section, updated the summary
1.9 05-11-2008 Added information about Windows HOSTS file modification and new worm names

Credits: Microsoft, AV vendors, Prevx Malware Center

  • Dan Guido

    I call bullshit:
    “Q: What is the mechanism in exploitation?
    A: Information was not disclosed, but drive-by download attacks, fake codec Web sites etc. are the very probable methods being used.”

    A fake codec website that uses an RPC vuln to gain execution? Seriously?

    I call bullshit again, this is useless info:
    “Q: Is there information about file sizes used during the attacks?
    A: Yes. The size is 397,312 bytes.
    Q: Are there any visual effects informing about the infection of the workstation?
    A: Information N/A. However, an end user can’t notify the infection.”

    Dozens of exploits are going to be out for this and not all of them are going to be 397 bytes. Same with the rest of the info. You should clearly delineate the difference between the vulnerability and its first exploit in your FAQ.

    “Q: Is the exploit code of this vulnerability publicly released?
    A: Yes. On Friday 24th October the proof of concept code was released on a blog of security researcher. The PoC has been released at several well-known exploit and security community Web sites too.”

    Might want to cite your sources. Their blog is full of information about the vuln:

  • Fred

    Stupid question, I know … but is Windows NT vulnerable?

  • Tuomas

    About Windows NT : NT is still vunerable to the previous server service problem ms06-040 (no security hotfixes to NT4), so there is no need to exploit this now one because the attacker can still exploit the old server service vunerability.

    But to answer the question, Windows nt is probably vunreable too but there is not going to be any official comment to that because NT is not supported operating system.

  • Hugo

    How does exploatation looks? Is there 60sec restarting of machine, like it was for blaster, if exploatation fails?

  • Juha-Matti

    Thanks for the feedback. Updates made and credits added.

  • Security

    Tuomas: Microsoft has released a patch for NT4 (customers with NT4 Custom Support Agreement only).

  • Thomas Lake

    @Fred: Yes NT is Vulnerable, but as Tuomas says, there won’t be any official report of it.

    @Hugo: Possibly, but the vulnerability allows for *arbitrary* code execution, as in they can do anything they like, not just kill the RPC service itself.

  • Martin

    Actually, there are patches available for those who have a support agreement for NT4: see

  • Fitzix

    The vulnerability is in the way that the Server service handles a particular RPC input.

    To clarify on a previous comment, the answer that this would come in the form of a codec as the most likely form of exploit is simply incorrect. This isn’t a client software exploit (although perhaps there are ways to make it that way) it’s a wormable exploit that could be used to remotely compromise a system over the LAN. Hence the recommendation to block ports.

    FAQs are great… but please make them accurate. Thanks. :)

  • Juha-Matti

    If there are readers participating MS’s NT4 Custom Support Agreement mentioned at
    please leave a comment if a patch for NT4.0 was delivered. Thanks!

  • Toni Koivunen

    No sane reverse engineer who’s taken a look at Gimmiv would call it sophisticated… It’s a buggy piece of crap and it’s a wonder they ever got it even compiled.

  • Conrad Longmore

    @Dan Guido

    A fake codec site won’t use the MS08-067 vuln itself, but the fake codec trojan could easily drop an exploit for this onto the victim’s machine.

    We tend to remember things like Sasser because that really only did spread through a peer-to-peer worm. But that was years ago, and we’re seeing much more in the way of multi-stage attacks.. especially since a lot of malware is modular these days.

    The truth is that it could come in via an infected laptop physically brought into the premises, tunnelled through a VPN client, dropped in via a drive-by download or email.. heck even an infected USB key or insecure WLAN would do the trick. There are probably 101 ways that this thing can get on your network.

  • Juha-Matti

    @Dan, the post was updated based to your feedback now. Additionally, information about the different file names and sizes (from 49kB to 417kB) has been added on 26th Oct.

  • DB

    If your computer gets infected, before you apply patch. If you then apply patch, will the patch, kill the infection?

  • Jason


    No. The vulnerability has already been exploited and the payload has been delivered. The payload will more than likely not require the vulnerability to function.

  • Daniel Clemens

    I love the way the word ‘infected’ is so easily thrown around in the use of a 0day to _compromise_ computers.

    Why can’t we use the word _compromise_ more , especially in cases like this.


  • John

    If using Exchange and you have RPC over HTTPs enabled, is it vulnerable?

  • Nathan

    John: RPC over HTTP is not vulnerable according to the MS Webcast of this issue.

  • reZident

    WatZ thiz malware..?..I don’t know…My OS not updating still may 2008..but no one virus or malware not infected MustDie.
    Simply, i’m nothing install official distributive it’z OS. I’m using nLite, bartpe e.t.c. progz and patching’n'skipping all installation’s files into .iso-image.
    Maybe, it’z really reason stability my system?
    What u r used tricks by defending your winOses, also?

    s0rry my english )

  • Jin

    Is there anyone experienced multiple user sessions on file server (Windows server 2003) after patching both? We have many users having 30~70 concurrent sessions opened to file servers. The only difference I can think of is patching both XP and Servers 2003.

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  • David S

    Q: Whats the best way to know if your macine(s) has been affected?

  • Website Upgradation Remodification

    Thank for Post,Sounds interesting, thx for the beautiful article.

  • fake rolex

    thank you for your post1

  • azeem

    what is the manual soulation for this problem or nay other hint without update that we can remove this vulnerability

    • azeem

      i m currently working on this problem of computers that causes this