As many of you who have been to my Hacking Exposed: Live presentations know, I like to demo a unique hack or release a new community tool during these presentations (this goes back to my days at Foundstone). This event is an example of a detection based on a custom rule. Starting with the directory C:\inetpub\wwwroot\aspnet_client\system_web\ location known from the Change Directory command in the initial detection, along with the matching directory from the NewScriptWritten EAM event, analysts began looking at files within that directory for potential webshells. The ECP Activity logs in figure 19 shows the request of the SetObject command for the OABVirtualDirectory pointing to the /ecp/y.js. If you were a fan of the old Foundstone tools, like Superscan, this is the guy who built them all! That's good to hear. However, these POSTs observed in the logs did not appear to be exploitation of CVE-2021-24085, and specifically we did not see additional evidence pointing to the CSRF Token generation (and subsequent privilege escalation) portion of CVE-2021-24085. However, the malicious payload is written to: C:\Users\XXXXXX\AppData\Local\Temp\Sxbyt.exe. This malicious activity is shown below in Figure 3. that identify and prevent fileless attacks that leverage bad behaviors. Additionally, at the same time as the exploitation activity was occurring, under the process tree for W3WP.EXE there were CSC.EXE (C# Command-Line Compiler) processes writing and compiling temporary DLLs on disk. CrowdStrike is a web/cloud based anti-virus which uses very little storage space on your machine. Configurations. And execution of this hash was blocked according to my blacklisting policy. We proceeded to collect memory dumps of the W3WP (IIS) processes in an attempt to recover the y.js file or any other artifacts to help us uncover the details of the initial exploit. Where the webshell is dropped successfully, it is then being used in post-exploitation activity. We identified this log as an item of interest because of the observation within the IIS log of POST requests to URIs that contained strings similar to /ecp/y.js. In this case, we want to define the parent image filename as cmd.exe and the image filename as calc.exe. However, you can define custom exclusions. with a naming pattern matching the regex string shown in Figure 6. Any guidance would be appreciated. Hamilton-CS 3 yr. ago the four zero-days in Exchange and we were able to correlate the activity observed by Falcon Complete as the now-reported zero-days and provide recommendations to our customers on how to patch to prevent further re-exploitation. Im going to go back to our client and double click. Monitoring File Changes with Falcon FileVantage, Falcon FileVantage for Security Operations, Falcon FileVantage: New CrowdStrike File Integrity Monitoring Solution Creates Total Efficiency for SecOps. No external or third-party tools are required. In this blog, we describe how the Falcon Complete team acted as an extension of our customers security teams to quickly detect and disrupt this sophisticated attack, which is still ongoing at the time of this blog publication. There are cases when you might want to block applications because you are certain that you never want them to run in your environment. Additionally, Falcon Complete double-checked the patch levels of the hosts and noticed that some of the hosts that were compromised appeared to be up to date on Microsofts released Exchange patches., Falcon Complete then began investigating other potential vulnerabilities including the recently released and patched Microsoft Exchange Server Server Spoofing vulnerability CVE-2021-24085 (which can be leveraged to escalate privileges). IOA Real World Example - Chinese Actor. Exchange 2016 Antivirus Exclusions. This is how this prevention shows up in the Falcon User Interface. Falcon Complete proceeded to continue to locate and remediate any webshells found and their associated build DLL files. Instead it looks at executing processes for malicious activities. The initial infection vector was still unknown at this point. In the Group Policy Management Editor go to Computer configuration, and then select Administrative templates. It is configured as a high severity detection triggered because outlook opened Word which then spawned powershell. Over time, CrowdStrike tunes and expands those built in indicators to offer immediate protection against the latest attacks. This section lists the file and folder exclusions that are delivered automatically when you install the File and Storage Services role. Custom and duplicate exclusions do not conflict with automatic exclusions. In this industry unexpected hurdles should be expected when responding to security events. Thank you very much for all the replies and the suggestions! This document and video will illustrate the power and flexibility of Custom IOAs (Indicators of Attack). This will prevent any execution of calc.exe from the command line. Choose one or both exclusion types: Detect/Prevent Upload Files to CrowdStrike A set of hosts that the exclusion applies to. New comments cannot be posted and votes cannot be cast. By default, there are no exemptions. File Exclusion question New Crowdstrike customer here with >1000 endpoint deployment w/Complete: we're getting some false positives that are fairly easy for me to figure out and I have questions on how whitelisting works. For more information, see Onboard Windows servers to the Microsoft Defender for Endpoint service. This indicated an attempt to bypass authentication and remotely execute code. Use with the offset parameter to manage pagination of results. They observed instances of an unknown attacker gaining unauthorized access to on-premises Microsoft Exchange application pools running on several hosts across multiple customer environments, and immediately commenced notifying affected organizations. In order to safeguard against this ongoing threat, CrowdStrike recommends organizations implement the following measures: We continue to work in close collaboration with our customers to respond swiftly to detect and disrupt this activity in order to stop these intrusion attempts from becoming breaches. Figure 6. This section lists the file type exclusions, folder exclusions, and the process exclusions that are delivered automatically when you install the Print Server role. Figure 4. Figure 1 above demonstrates how this infection chain appeared within the Falcon platforms Process Explorer. Part of the Falcon Complete teams initial recommended recovery actions was to patch this host with the most recent available updates. If you have folders and files types that you wish to exclude from the behaviour engine then these can be manually added in the management console. In nearly all instances, the webshell dropped was observed to be a China Chopper-like webshell.. Select Your University. See unauthorized modifications to all relevant critical system, configuration and content files. As a new Crowdstrike customer (who hasn't been onboarded yet), it is not clear to me whether or not those recommendations from Microsoft (and other software vendors) are even applicable in a Crowdstrike protected environment. The following sections contain the exclusions that are delivered with automatic exclusions file paths and file types. Falcon Complete immediately began pulling the IIS logs from the impacted hosts to search for artifacts in an attempt to confirm the initial entry vector. Exclude the following installation folders and their sub-folders from on-access virus scan. Staff can quickly target file change data with any relevant adversary activity. The tool was originally written to support our CrowdStrike Services team during their incident response engagements. At the 2014 RSA Conference in San Francisco, CrowdStrike CTO Dmitri Alperovitch and I presented the security community with a demo of CrowdResponse during the Hacking Exposed: Day of Destruction talk. During our timelining process we reviewed the Application Event Logs and we were able to identify further log sources to pivot to that helped build a bigger picture of the exploitation: Event ID 47 MSExchange Control Panel: Administrator SID being used indicating privilege escalation has occurred, Event ID 4007 MSComplianceAudit: This entry pointed to an Exchange audit log contained with the following filepath:, %PROGRAMFILES%\Microsoft\Exchange Server\V15\Logging\LocalQueue\Exchange\. Looking around the timestamps that these files were written, Falcon Complete uncovered a pattern of behavior in multiple customers IIS logs, thus indicating that this log pattern likely has to do with the exploitation activity.. We will be releasing additional CrowdStrike adversary indicators over the coming months in our blog posts, along with their associated YARA rules that can be feed directly into CrowdResponse. . Additional paths observed are included in the IOC section below., C:\inetpub\wwwroot\aspnet_client\system_web\, location known from the Change Directory command in the initial detection, along with the matching directory from the NewScriptWritten EAM event, analysts began looking at files within that directory for potential. These folders are specified by the registry key HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\DFSR\Parameters\Replication Groups\GUID\Replica Set Configuration File. Next, we pivoted to analysis of the ECP server logs. tool, but with extra baked-in goodness! The exceptions we do have are for detections that cause a lot of excessive false positives in the console. Open Windows Defender Security Center. Ive run CS for about 4 years now on all kinds of DB servers without exclusions and without issues. Eventually, all three policies are assigned to the same user. Files in the File Replication Service (FRS) working folder. I firmly believe in giving back to the security community. Im going to highlight both of them. This kind of attack a previously unknown threat from a highly sophisticated adversary presents one of the most challenging situations a security team will encounter.. See Configure the list of exclusions based on folder name or file extension. Grey Area of Exclusion: Once we reviewed the detection information at hand and confirmed that the activity noted was malicious, the next step was to identify the full scope of this activity. You can find more information in our documentation (login required, not sure if you have one ahead of onboarding): https://falcon.crowdstrike.com/support/documentation/68/detection-and-prevention-policies#file-exclusions. We were now armed with two facts: first, the webshells remediated from the hosts appeared to be Microsoft Exchange Server Offline Address Book (OAB) config files with a China Chopper-like shell in the External URL portion; second, POSTs to DDIService.svc/SetObject that set the OABVirtualDirectory did not match any known vulnerabilities to Microsoft Exchange that CrowdStrike was aware of. Joining the Falcon Complete team is the CrowdStrike Falcon OverWatch team of proactive threat hunters, who are imperative in providing early visibility into this new emerging threat, along with the CrowdStrike Intelligence team. Triaging that audit log provided us further insight into the exploitation process, specifically the dropping of webshells by an Administrator account using Set-OabVirtualDirectory to modify the External URL field with the Chopper Shell script. However, these POSTs observed in the logs did not appear to be exploitation of. Figure 17. Further analysis revealed that this webshell was consistent with variants related to a. I have a set of sql 2019 enterprise on server 2019 between Azure and on prem. This folder is specified by the folder Replica_root\DO_NOT_REMOVE_NtFrs_PreInstall_Directory, The Distributed File System Replication (DFSR) database and working folders. Welcome to the CrowdStrike subreddit. In Analysis Manager, right-click the server, and then select Properties. This section lists the default exclusions for all roles in Windows Server 2016, Windows Server 2019, and Windows Server 2022. A list of the hashes along with the selected policy, in this case always block is visible from the Configuration -> Prevention Hashes dashboard. If individual hashes need to be edited select the box next to the chosen hash and hit the apply policy button at the top. For wildcards, use current Windows operating system standards: Wildcards can be used for file and folder paths. Our Endpoint Activity Monitor (EAM) application gives the Falcon Complete team and Falcon platform customers the ability to search this execution data in real time, and to quickly investigate and scope the extent of compromise. Falcon uses multiple methods to prevent and detect malware. The entry details can be found using bpgetconfig or nbgetconfig command. Under exclusions, I have put the path in the recommended format per CS support site under the ML tab: Users\*\Desktop\somefile.exe as well as scoped the exclusion to only affect one Group. Configuration file this section lists the file and storage Services role are specified by registry... With automatic exclusions expected when responding to security events actions was to patch this host with the recent... Windows crowdstrike file path exclusion system standards: wildcards can be found using bpgetconfig or command. You install the file and folder paths hit the apply policy button at the top exploitation. 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