I've lost my sense of urgent concern for my IIS servers by installing and configuring the URLScan program MS released. I can now see in the log files that it generates each attempt to penitrate and have for the past two years (since installing it) seen no successful intrusion on my IIS servers. Its free. It logs. Best of all, it seems to work! Configuring it was not to easy until I understood it. Is there a reason for the lack of wide spread use of this utility? ----- Original Message Follows ----- > OK, > > Now I have done my homework much better ;) > > On the 593 event, only the newest versions of Windows > support the image name inside it: > > Win Version Image file name included in 593 > NT 4 No > Win2K No > XP Yes > NET Server Yes (now called Windows 2003 > Server) > > So with XP (great server platform ;)) and Windows 2003 > Server (when available) we can detect (happened) > intrusions by looking at the 593 events. If they are from > the IUSR_xxx account and not for known valid files, we > most likely have become hacked. > > BTW: with Windows 2003 Server (RC1), the process is still > being tracked as initiated by local SYSTEM. > > With NT4 and Windows 2000, this does NOT work. The 593's > don't have the image name in them and the 592 don't have > the correct user. If that is a dedicated machine with just > IIS running, we might still be able to use the 592's and > live with some false alarms - but that needs to be decided > by the admin. > > Fortunately, I found another way to track those > executions. It has a larger performance hit, but it works. > I tested it on Windows 2000 only, so there might be some > issues with other Windows version (I'd say I doubt so if I > hadn't had today's experience... ;)). > > It works via file system auditing. I use file audit events > , specifically "execution" type to see if IUSR_xxx > accesses the file. I can do so because interestingly > Windows logs the right user id with the file opens [but > not with the later process creation... Well, let me dig > out my win32 api - or is process creation first and then > the image being loaded into memory. I think so (but not > totally sure). If so, we now know where in its workflow > IIS does the actual impersonation ;)]. I use the 560 > Security events. To enable this, you need to > > A) go to system policies/audit policies and enable "object > access" auditing. > If this is not enabled, file access audits will not > show up even if enabled in NTFS > B) go to explorer (or your favourite file manager) and > select the files/directories that > should be auditied. For example the \winnt directory. > Click properties, click security, > click advanced, click auditing, click add, type > IUSR_xxx, click OK, now select "Execute", > click OK (make sure you have this set to inherit) > > Now you have turned on file system auditing for the > IUSR_xxx account. This will generate those nice > 560/Security events that show you which files the web user > accesses. Unfortunately, this is more than you got with > process tracking, for example it includes all DLLs (ODBC, > winsock and so on)loaded by the web application. You can > either turn off auditing for those via the OS tool > (explorer, if you like clicking) or some other tool to do > it via the command line. Or you can have these events > reported to the event log and then, during your analysis > of the event log, ignore everything that is not an exe > file (or whatever else you are after). > > Once you have done this setup, you can setup a process to > (frequently!) read the nt event log and look for those > 560's from source "Security" in the security event log > that > > - were created from the IUSR_xxx account > - are in respect to an exe or whatever else you see fit > - are NOT falid exes as again perl.exe or php.exe (be sure > to use the full path!) > > If you find some of those, chances are good you have just > then been hacked. So it would be a good time to forward > that specific event log entry to the admin via email (or > whatever else you like). Of course, the filter might need > a little fine tuning, but it should work pretty well. As > we all hope that those warnings will never appear, it is a > good idea to test you filter with some test script that > access a file deemed as "evil" ;) > > I am proposing this "IIS monitor" as a kind of last resort > to positively detect that you have been hacked. So it > should at least save you from the hassle of detecting a > security breach too late. Again, it most probably won't > help in preventing the incident - but can aid in timely > response. > > As such, I hope you find the outlined procedure useful... > > Ah, yes, it works with IIS only, at least as of my (very > limited) testing with Apache 1.3.27 under win32. But some > of the Apache folks might proove me to be wrong. > > Rainer Gerhards > Adiscon > > > -----Original Message----- > > From: Rainer Gerhards > > Sent: Friday, January 17, 2003 2:10 PM > > To: 'loganalysisat_private' > > Cc: Rainer Gerhards; 'Tina Bird'; 'Marcus J. Ranum'; > > 'probertsat_private'; 'Ben Laurie'; > > 'ericfat_private' Subject: RE: NT Event Log > > and Web Server Attacks > > > > Arrghhh... > > > > Did Tina have on of those "don't type faster than you > > think" quotes in her sig... Actually, I verfified what > > I wrote under Windows XP (not the typical server > > platfrom). On the Win2K server boxes, there is a little > > problem with the 593 event: it does not have the exe > > file name in it. I verified this on Germany W2K Server > > SP3 Buuild 2195. Obviously the file name got added in > > XP (and so hopefully is in .NET server or Windows 2003 > > Server as it is called now.) I am just posting this for > all who might be banging their had finding the file > > name... > > Seems not to be my day. Maybe I should can my posts and > > re-read and finally post them tomorrow ;) > > > > Sorry, > > Rainer Gerhards > > > > > -----Original Message----- > > > From: Rainer Gerhards > > > Sent: Friday, January 17, 2003 2:04 PM > > > To: Rainer Gerhards > > > Subject: RE: NT Event Log and Web Server Attacks > > > > > > > > > Unfortunately, I need to post a correction on this > > > issue. That correction does also address some issues > > > with NT Event logging & IIS in general, so maybe Eric > > > would like to jump in? > > > The fact to correct is the user that is logged in nt > > > event log. Interestingly, when the process (the exe > > > file) is started, that is not the expected IUSR_xxx > > > account, but the build-in SYSTEM account. I have > > > verified (with cmd.exe) this is not only the case for > > > script processors like perl, but with any program > > > (well, at least cmd.exe...). > > > The reason seems to be that IIS triggers the 592 event > > > (process creation) while NOT being impersonated as the > > > actual user this request runs under. Then, in some > > > stage further down the workflow, IIS impersonates as > > > the actual user (IUSR_xxx in our case). It is still > > > impersonated when the end process is logged via event > > > 593, which therefore specifies the IUSR_xxx as the > > > user in question. > > > In my personal view, IIS should log the 592 event > > > under the actual user, too and not under the system > > > context. This also raises the question (which I do > > > not intend to discuss) if IIS is really able to > > > ensure NTFS ACLS under all circumstances - or if a > > > failing stage (the one looking up ACLs) of IIS could > lead to the execution of a file that the actual user (e.g. > > > IUSR_xxx) is not intended to. This for sure would > > > require a vulnerability in the ACL lookup stage, but > > > there could be some over time... > > > > > > Actually, this finding makes the intrusion detection > > > rule harder. We know need to rule out other occasions > > > where the build-in SYSTEM account (validly) executes > > > programs. This seems not to be very practical. So we > > > can resort to using the 593 (process termination). > > > They still do have the name of the file being > > > executed and also have the correct user id in them. > > > The only problem here is that we won't detect > processes that were started by the intruder but NEVER > > > ENDED. Anyhow, I am looking to catch (not yet known, > > > maybe not even existing) vulnerabilities and their > > > exploits in IIS that will be used to start an > > > intrusion. One of the most common things I can think > > > of is calling cmd.exe. That one most probably > > > terminates. Most of the attacks I know start with > calling cmd.exe or a similar program. One, that > > > terminates. Only after a number of requests, a > > > non-terminating program like a remote shell or a tftp > > > server is started. Of course, if a buffer overrun is > > > used to execute a non-terminating program, or a > > > looping batch file is executed, chances are good we > will NOT see any process termination events. In any case, > > > the 593 still provides a good warning sign, altough > > > the 592 would be better (if it had the correct user > > > id in it...). > > > I will probably play a little more with this issue and > > > post new results - if any. > > > > > > My apologies for the initial mistake and the time it > > > took to post this correction. I hope I miss-lead > > > nobody ;) > > > Rainer Gerhards > > > Adiscon > > > > > > > -----Original Message----- > > > > From: Rainer Gerhards > > > > Sent: Friday, January 17, 2003 12:26 PM > > > > To: Rainer Gerhards > > > > Subject: NT Event Log and Web Server Attacks > > > > > > > > > > > > Hi all, > > > > > > > > I just wanted to let the list know of a way to > > > > detect intrusions via IIS. It may work for other > > > > web servers, too. > > > > We have just build a new rule to use the nt event > > > > log to detect (so far unknown) attacks... Well > > > > effectively, we detect intrusions after they > > > > happend. So the intruder most probably already got > > > > in. This will not save you from the intrusion, but > > > > at least you know you need to react. > > > > For it to work, we assume the following: > > > > > > > > 1. IIS process tracking is activated (and hopefully > > > > works reliable enough ;)) > > > > 2. The web site is accessed by anonymous users, only > > > > 3. The server is a dedicated web server > > > > > > > > If 2 or 3 are not the case, we can probably still > > > > use the same idea, but the filter needs to be more > > > > advanced. > > > > It is important to know that anonymous requests are > > > > run in the security context of a specifically > > > > designated NT account. In most cases this is the > > > > IUSR_xxx account where xxx is typically the machine > > > > name. This account can be configured in the IIS > > > > admin console. So you need to lookup the details > > > > there. What we now do is we look at the event log > > > > in short intervals. When we detect a program start > > > > (security event log, source "Security", event id > > > > 592) AND the user is the IUSR_xxx account AND it is > > > > not a program we know IIS needs to run (e.g. > > > > perl.exe is run for PERL scripts; php.exe is for > > > > PHP scripts) then chances are very high that someone > has successfully intruded our machine via IIS. So it > > > > would probably be a good idea to forward the event > > > > log record to an admin in charge (via email or > > > > whatever). > > > > I hope this is helpful. As always, comments are very > > > > welcome. I would particularly like to know if that > > > > works with Apache under win32 ;) > > > > > > > > Rainer Gerhards > > > > Adiscon > > > > > > > > > > _______________________________________________ > LogAnalysis mailing list > LogAnalysisat_private > http://lists.shmoo.com/mailman/listinfo/loganalysis =========================== Kevin W. Gagel Network Administrator College of New Caledonia gagelat_private (250) 561-2131 loc 448 -------------------------------- The College of New Caledonia Visit us at http://www.cnc.bc.ca -------------------------------- _______________________________________________ LogAnalysis mailing list LogAnalysisat_private http://lists.shmoo.com/mailman/listinfo/loganalysis
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