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	"title": "Threat Spotlight: Rombertik - Gazing Past the Smoke, Mirrors, and Trapdoors",
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	"plain_text": "Threat Spotlight: Rombertik - Gazing Past the Smoke, Mirrors,\r\nand Trapdoors\r\nBy Talos Group,\r\nPublished: 2015-05-04 · Archived: 2026-04-05 16:49:47 UTC\r\nThis post was authored by Ben Baker and Alex Chiu.\r\nExecutive Summary\r\nThreat actors and security researchers are constantly looking for ways to better detect and evade each other.  As\r\nresearchers have become more adept and efficient at malware analysis, malware authors have made an effort to\r\nbuild more evasive samples.  Better static, dynamic, and automated analysis tools have made it more difficult for\r\nattackers to remain undetected. As a result, attackers have been forced to find methods to evade these tools and\r\ncomplicate both static and dynamic analysis.\r\nTable of Contents\r\nExecutive Summary\r\nThe 10,000 Foot View at Rombertik\r\nAnalysis\r\nA Nasty Trap Door\r\nThe Actual Malware\r\nCoverage and Indicators of Compromise\r\nConclusion\r\nIt becomes critical for researchers to reverse engineer evasive samples to find out how attackers are attempting to\r\nevade analysis tools. It is also important for researchers to communicate how the threat landscape is evolving to\r\nensure that these same tools remain effective. A recent example of these behaviors is a malware sample Talos has\r\nidentified as Rombertik. In the process of reverse engineering Rombertik, Talos discovered multiple layers of\r\nobfuscation and anti-analysis functionality. This functionality was designed to evade both static and dynamic\r\nanalysis tools, make debugging difficult. If the sample detected it was being analyzed or debugged it would\r\nultimately destroy the master boot record (MBR).\r\nTalos’ goal is to protect our customer’s networks.  Reverse engineering Romberik helps Talos achieve that goal by\r\nbetter understanding how attackers are evolving to evade detection and make analysis difficult.  Identifying these\r\ntechniques gives Talos new insight and knowledge that can be communicated to Cisco’s product teams.  This\r\nknowledge can then be used to harden our security products to ensure these anti-analysis techniques are\r\nineffective and allow detection technologies to accurately identify malware to protect customers.\r\nThe 10,000 Foot View at Rombertik\r\nhttp://blogs.cisco.com/security/talos/rombertik\r\nPage 1 of 9\n\nAt a high level, Romberik is a complex piece of malware that is designed to hook into the user’s browser to read\r\ncredentials and other sensitive information for exfiltration to an attacker controlled server, similar to Dyre.\r\nHowever, unlike Dyre which was designed to target banking information, Rombertik collects information from all\r\nwebsites in an indiscriminate manner.\r\nRombertik has been identified to propagate via spam and phishing messages sent to would-be victims.  Like\r\nprevious spam and phishing campaigns Talos has discussed, attackers use social engineering tactics to entice users\r\nto download, unzip, and open the attachments that ultimately result in the user’s compromise.\r\nFigure 1: Email messages such as the one seen here are spammed out in the hopes that users will\r\nopen them and open the attachments. This is one sample that was used to propagate Rombertik.\r\nIn this sample, the message observed in Rombertik’s distribution appears to come from the “Windows\r\nCorporation,” an organization that possesses “state-of-the-art manufacturing quality processes.”  The attackers\r\nattempt to convince the user to check the attached documents to see if their business aligns with the target user’s\r\norganization.  If the user downloads and unzips the file, the user then sees a file that looks like a document\r\nthumbnail.\r\nhttp://blogs.cisco.com/security/talos/rombertik\r\nPage 2 of 9\n\nWhile this file may appears to be some sort of PDF from the icon or thumbnail, the file actually is a .SCR\r\nscreensaver executable file that contains Rombertik.  Once the user double clicks to open the file, Rombertik will\r\nbegin the process of compromising the system.\r\nThe process by which Rombertik compromises the target system is a fairly complex with anti-analysis checks in\r\nplace to prevent static and dynamic analysis.  Upon execution, Rombertik will stall and then run through a first set\r\nof anti-analysis checks to see if it is running within a sandbox.  Once these checks are complete, Rombertik will\r\nproceed to decrypt and install itself on the victims computer to maintain persistence.  After installation, it will then\r\nlaunch a second copy of itself and overwrite the second copy with the malware’s core functionality.  Before\r\nRombertik begins the process of spying on users, Rombertik will perform once last check to ensure it is not being\r\nanalyzed in memory.  If this check fails, Rombertik will attempt to destroy the Master Boot Record and restart the\r\ncomputer to render it unusable.  The graphic below illustrates the process.\r\nFigure 2: An illustration of the step-by-step process Rombertik follows to compromise the target\r\nsystem.\r\nAnalysis\r\nFrom the beginning, Rombertik incorporates several layers of obfuscation along with anti-analysis functionality.\r\n Obfuscating the functionality of a malware sample can be accomplished in many different ways.  A common\r\nmethod is to include garbage code to inflate the volume of code an analyst might have to review and analyze.  In\r\nthis case, the unpacked Rombertik sample is 28KB while the packed version is 1264KB. Over 97% of the packed\r\nfile is dedicated to making the file look legitimate by including 75 images and over 8000 functions that are never\r\nused. This packer attempts to overwhelm analysts by making it impossible to look at every function.\r\nhttp://blogs.cisco.com/security/talos/rombertik\r\nPage 3 of 9\n\nFigure 3: This chart shows the breakdown of the Rombertik executable and how it contains a large\r\namount of unnecessary code and data.\r\nAs we started to slowly peel back the layers and focus on the subset of functions that are actually used, we\r\nobserved an interesting sandbox evasion technique. A common technique to evade sandboxes is to sleep for\r\nextended lengths of time with the intention of forcing the sandbox to time out before the malware “wakes up” and\r\nbegins executing.  In response, sandboxes got better at detecting and responding when malware slept for extended\r\nperiods of time.  Rombertik employs a similar approach to delay execution, but does so without sleeping.\r\n Rombertik instead writes a byte of random data to memory 960 Million times.  This is designed to consume time,\r\nlike sleeping, but presents a couple disadvantages for sandboxes and application tracing tools.  Sandboxes may not\r\nbe able to immediately determine that the application is intentionally stalling since it’s not sleeping.  The other\r\ndisadvantage is that the repetitive writing would flood application tracing tools.  If an analysis tool attempted to\r\nlog all of the 960 Million write instructions, the log would grow to over 100 gigabytes. Even if the analysis\r\nenvironment was capable of handling a log that large, it would take over 25 minutes just to write that much data to\r\na typical hard drive.  This complicates analysis.\r\nAfter intentionally stalling by writing to memory repeatedly, Rombertik checks to see if analysis tools have\r\nmodified code in the Windows API ZwGetWriteWatch routine.  It does this by calling ZwGetWriteWatch with\r\ninvalid arguments.  If the routine does not return with a specific error, Rombertik terminates. The assumption\r\nbehind checking for a specific error versus a generic error is to check for sandboxes that suppress errors returned\r\nfrom API routine calls.   Once the sandbox check is complete, Rombertik calls the Windows API\r\nhttp://blogs.cisco.com/security/talos/rombertik\r\nPage 4 of 9\n\nOutputDebugString function 335,000 times as an anti-debugging mechanism.  Finally, an anti-analysis function\r\nwithin the packer is called to check the username and filename of the executing process for strings like “malwar”,\r\n“sampl”, “viru”, and “sandb”. If the packer detects any of these substrings, it will stop unpacking and terminate.\r\n At this point, the initial anti-analysis checks are complete.\r\nOnce the packer has run through initial anti-analysis checks, it will check to see if it is executing from\r\n%AppData%\\rsr\\yfoye.exe.  If the packer is not executing from there, it will proceed to install itself in order to\r\nensure persistence across system reboots before continuing on to execute the payload. To install itself, Rombertik\r\nfirst creates a VBS script named “fgf.vbs”, which is used to kick off Rombertik every time the user logs in, and\r\nplaces the script into the user’s Startup folder.  Rombertik then creates %AppData%\\rsr\\yfoye.bat and moves the\r\npacked version of itself into %AppData%\\rsr\\yfoye.exe.\r\nIf Rombertik detects it is already executing from %AppData%\\rsr\\yfoye.exe, the malware will then begin\r\ndecrypting and executing the main unpacking code in memory.  Rombertik will then proceed to execute yfoye.exe\r\na second time to create a new instance of the process.  Once the unpacking is complete, Rombertik will overwrite\r\nthe memory of the new process with the unpacked executable code.  The unpacking code is monstrous and has\r\nmany times the complexity of the anti-analysis code.  The code contains dozens of functions overlapping with\r\neach other and unnecessary jumps added to increase complexity. The result is a nightmare of a control flow graph\r\nwith hundreds of nodes.  Figure 4 helps illustrate how complex the unpacking code is in comparison to the all the\r\ncode that performs anti-analysis checks.\r\nFigure 4: The control flow graph on the left represents the interwoven functions within the\r\nunpacking code that’s decrypted to memory. The control flow graph on the right represents the\r\nhttp://blogs.cisco.com/security/talos/rombertik\r\nPage 5 of 9\n\npreviously mentioned anti-analysis checks. These 23 basic blocks represent the 930 million writes,\r\n335 thousand API calls, checking ZwGetWriteWatch, and checking file and usernames. All of this\r\nfunctionality fits in this rather simple graph, where the red block is only executed if all of the checks\r\nwere satisfied. A typical function has less than 20 nodes (basic blocks) and would normally be easy\r\nto see how all basic blocks relate to each other.\r\nA Nasty Trap Door\r\nOnce the unpacked version of Rombertik within the second copy of yfoye.exe begins executing, one last anti-analysis function is run — which turns out to be particularly nasty if the check fails.  The function computes a 32-\r\nbit hash of a resource in memory, and compares it to the PE Compile Timestamp of the unpacked sample. If the\r\nresource or compile time has been altered, the malware acts destructively. It first attempts to overwrite the Master\r\nBoot Record (MBR) of PhysicalDisk0, which renders the computer inoperable. If the malware does not have\r\npermissions to overwrite the MBR, it will instead destroy all files in the user’s home folder (e.g. C:\\Documents\r\nand Settings\\Administrator\\) by encrypting each file with a  randomly generated RC4 key. After the MBR is\r\noverwritten, or the home folder has been encrypted, the computer is restarted.\r\nThe Master Boot Record starts with code that is executed before the Operating System. The overwritten MBR\r\ncontains code to print out “Carbon crack attempt, failed”, then enters an infinite loop preventing the system from\r\ncontinuing to boot.\r\nThe MBR also contains information about the disk partitions. The altered MBR overwrites the bytes for these\r\npartitions with Null bytes, making it even more difficult to recover data from the sabotaged hard drive.\r\nOnce the computer is restarted, the victim’s computer will be stuck at this screen until the Operating System is\r\nreinstalled:\r\nhttp://blogs.cisco.com/security/talos/rombertik\r\nPage 6 of 9\n\nEffectively, Rombertik begins to behave like a wiper malware sample, trashing the user’s computer if it detects it’s\r\nbeing analyzed.  While Talos has observed anti-analysis and anti-debugging techniques in malware samples in the\r\npast, Rombertik is unique in that it actively attempts to destroy the computer’s data if it detects certain attributes\r\nassociated with malware analysis.\r\nThe Actual Malware\r\nAt this point, Rombertik will assume that all anti-analysis checks have passed and will actually begin doing what\r\nwas originally intended — stealing user data.  Rombertik will scan the user’s currently running process to\r\ndetermine if a web browser is currently running.  If Rombertik detects an instance of Firefox, Chrome, or Internet\r\nExplorer, it will inject itself into the process and hook API functions that handle plain text data. Once\r\naccomplished, Rombertik is then able to read any plain-text data the user might type into their browser and\r\ncapture this input before it gets encrypted if the input is to be sent over HTTPS. This enables the malware to\r\ncollect data such as usernames and passwords from almost any website.  Rombertik does not target any site in\r\nparticular, such as banking sites, but instead, attempts to steal sensitive information from as many websites as\r\npossible.  The collected data is then Base64 encoded and forwarded to www.centozos.org.in/don1/gate.php (in this\r\nhttp://blogs.cisco.com/security/talos/rombertik\r\nPage 7 of 9\n\nexample) over HTTP with no encryption.\r\nCoverage and Indicators of Compromise\r\nSample Analysed (SHA256)\r\n0d11a13f54d6003a51b77df355c6aa9b1d9867a5af7661745882b61d9b75bccf\r\nCommand-and-Control Servers\r\nwww.centozos[.]org[.]in\r\nConclusion\r\nRombertik is a complex piece of malware with several layers of obfuscation and anti-analysis functionality that is\r\nultimately designed to steal user data.  Good security practices, such as making sure anti-virus software is installed\r\nand kept up-to-date, not clicking on attachments from unknown senders, and ensuring robust security policies are\r\nin place for email (such as blocking certain attachment types) can go a long way when it comes to protecting\r\nusers.  However, a defense in depth approach that covers the entire attack continuum can help identify malware\r\nand assist in remediation in the event that an attacker finds a way to evade detection initially.\r\nFor Talos, understanding how malware changes and evolves is essential to developing detection content and\r\nensuring that static, dynamic, and automated analysis tools remain effective. We must adapt, change, and respond\r\naccordingly to address the evolving threat landscape. Looking forward, Talos expects these methods and behaviors\r\nto be adopted by other threat actors in the future.\r\nProtecting Users From These Threat\r\nhttp://blogs.cisco.com/security/talos/rombertik\r\nPage 8 of 9\n\nWe encourage organizations to consider security best practices,\r\nstarting with a threat-centric approach that implements protections across the extended network and across the full\r\nattack continuum.\r\nESA can block malicious emails, including phishing and malicious attachments sent by threat actors.\r\nCWS/WSA web scanning prevents access to websites hosting malicious content.\r\nAdvanced Malware Protection (AMP) is designed to prevent the execution of the malware used by these threat\r\nactors.\r\nNetwork Security appliances, such as NGIPS and NGFW, have signatures to detect and block malicious network\r\nactivity by threat actors.\r\nSource: http://blogs.cisco.com/security/talos/rombertik\r\nhttp://blogs.cisco.com/security/talos/rombertik\r\nPage 9 of 9",
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	"sources": [
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