Netskope achieves FedRAMP High Authorization. Netskope GovCloud.

The platform of the future is Netskope

Intelligent Security Service Edge (SSE), Cloud Access Security Broker (CASB), Cloud Firewall, Next Generation Secure Web Gateway (SWG), and Private Access for ZTNA built natively into a single solution to help every business on its journey to Secure Access Service Edge (SASE) architecture.

Go to Products Overview
Netskope video
Next Gen SASE Branch is hybrid — connected, secured, and automated

Netskope Next Gen SASE Branch converges Context-Aware SASE Fabric, Zero-Trust Hybrid Security, and SkopeAI-powered Cloud Orchestrator into a unified cloud offering, ushering in a fully modernized branch experience for the borderless enterprise.

Learn about Next Gen SASE Branch
People at the open space office
Designing a SASE Architecture For Dummies

Get your complimentary copy of the only guide to SASE design you’ll ever need.

Get the eBook
Embrace a Secure Access Service Edge (SASE) architecture

Netskope NewEdge is the world’s largest, highest-performing security private cloud and provides customers with unparalleled service coverage, performance and resilience.

Learn about NewEdge
Your Network of Tomorrow

Plan your path toward a faster, more secure, and more resilient network designed for the applications and users that you support.

Get the white paper
Your Network of Tomorrow
Netskope Cloud Exchange

The Netskope Cloud Exchange (CE) provides customers with powerful integration tools to leverage investments across their security posture.

Learn about Cloud Exchange
Netskope video
Make the move to market-leading cloud security services with minimal latency and high reliability.

Learn about NewEdge
Lighted highway through mountainside switchbacks
Safely enable the use of generative AI applications with application access control, real-time user coaching, and best-in-class data protection.

Learn how we secure generative AI use
Safely Enable ChatGPT and Generative AI
Zero trust solutions for SSE and SASE deployments

Learn about Zero Trust
Boat driving through open sea
Netskope achieves FedRAMP High Authorization

Choose Netskope GovCloud to accelerate your agency’s transformation.

Learn about Netskope GovCloud
Netskope GovCloud
  • Resources chevron

    Learn more about how Netskope can help you secure your journey to the cloud.

  • Blog chevron

    Learn how Netskope enables security and networking transformation through security service edge (SSE).

  • Events & Workshops chevron

    Stay ahead of the latest security trends and connect with your peers.

  • Security Defined chevron

    Everything you need to know in our cybersecurity encyclopedia.

Security Visionaries Podcast

Cookies, Not Biscuits
Host Emily Wearmouthas sits down with experts David Fairman and Zohar Hod to discuss the past, present, and future of internet cookies.

Play the podcast
Podcast: Cookies, Not Biscuits
Latest Blogs

How Netskope can enable the Zero Trust and SASE journey through security service edge (SSE) capabilities.

Read the blog
Sunrise and cloudy sky
SASE Week 2023: Your SASE journey starts now!

Replay sessions from the fourth annual SASE Week.

Explore sessions
SASE Week 2023
What is Security Service Edge?

Explore the security side of SASE, the future of network and protection in the cloud.

Learn about Security Service Edge
Four-way roundabout
We help our customers to be Ready for Anything

See our Customers
Woman smiling with glasses looking out window
Netskope’s talented and experienced Professional Services team provides a prescriptive approach to your successful implementation.

Learn about Professional Services
Netskope Professional Services
The Netskope Community can help you and your team get more value out of products and practices.

Go to the Netskope Community
The Netskope Community
Secure your digital transformation journey and make the most of your cloud, web, and private applications with Netskope training.

Learn about Training and Certifications
Group of young professionals working
  • Company chevron

    We help you stay ahead of cloud, data, and network security challenges.

  • Why Netskope chevron

    Cloud transformation and work from anywhere have changed how security needs to work.

  • Leadership chevron

    Our leadership team is fiercely committed to doing everything it takes to make our customers successful.

  • Partners chevron

    We partner with security leaders to help you secure your journey to the cloud.

Supporting sustainability through data security

Netskope is proud to participate in Vision 2045: an initiative aimed to raise awareness on private industry’s role in sustainability.

Find out more
Supporting Sustainability Through Data Security
Highest in Execution. Furthest in Vision.

Netskope recognized as a Leader in the 2023 Gartner® Magic Quadrant™ for Security Service Edge.

Get the report
Netskope recognized as a Leader in the 2023 Gartner® Magic Quadrant™ for Security Service Edge.
Thinkers, builders, dreamers, innovators. Together, we deliver cutting-edge cloud security solutions to help our customers protect their data and people.

Meet our team
Group of hikers scaling a snowy mountain
Netskope’s partner-centric go-to-market strategy enables our partners to maximize their growth and profitability while transforming enterprise security.

Learn about Netskope Partners
Group of diverse young professionals smiling

Anatomy of a Ransomware Attack: Cerber Uses Steganography to “Hide in Plain Sight”

Jun 30 2016
Cloud Best Practices
Cloud Malware
Cloud Security
Netskope Threat Research Labs
Office 365 Security
Tools and Tips
Vulnerability Advisory

Ransomware is a hot topic and it’s about to become hotter. Why? Because now it’s targeting our cloud services. Nearly one out of five malware detections in the past month in the Netskope Active Platform are document files such as Microsoft Word that contain macros. Earlier this week, cloud platform vendor Avanan blogged about a widespread ransomware attack, called Cerber, that is being spread via cloud productivity platform, Microsoft Office 365. Incidentally, we have seen these types of macro-type malware-delivered ransomware across a variety of cloud-based file-sharing apps, and we don’t believe there’s anything necessarily unique about detecting it in Office 365. The name Cerber is derived from Cerberus, a 3-headed dog that guards the entrance to Hades in Greek mythology.

Fig 1 - Cerber ransomware

Figure 1: Image from Cerber ransomware note

The attacks use a decoy document loaded with malicious macro code that downloads Cerber malware files to users’ machines. When the decoy document is opened, it drops a VBScript file (.vbs) with a random name in the format “%APPDATA%\%RANDOM%.vbs.” The VBScript file is then launched using wscript.exe, which downloads an image file named “mhtr.jpg.” This jpeg image is downloaded from the URLs solidaritedeproximite[.]org/mhtr.jpg, 92.222.104[.]182/mhtr.jpg. If the file is not found when visiting solidaritedeproximite[.]org, it will be fetched from 92[.]222[.]104[.]182 as shown in Figure 2 below. At the time of writing this blog, solidaritedeproximite[.]org was not serving the file and was instead delivered from 92[.]222[.]104[.]182.

Figure 2 - cerber ransomewareFigure 3 - cerber ransomeware

Figure 2: Network packet capture displaying attempts to the URLs used to download mhtr.jpg

The image file mhtr.jpg looks benign and displays content related to “zen-coding,” as shown in Figure 3, but has steganographically (hidden in plain sight) embedded malware inside it which is decoded to an exploit as shown in Figure 4. This technique has been used by such historic malware families as Bredolab, but is seeing a resurgence as it permits executables to be transmitted without causing network monitoring devices to suspect malicious activity.

Fig 3 - cerber ransomeware

Figure 3: Image that would be displayed if someone opened mhtr.jpg

Fig 3b - Cerber Ransomeware

Fig 4 - Cerber Ransomware

Figure 4: JFIF image and the encoded blob of mhtr.jpg

At the time of writing this blog, very few security vendors were detecting this image file as shown from the VirusTotal page in Figure 5.

Fig 5- Cerber ransomeware

Figure 5: mhtr.jpg sample detection in VirusTotal

In the next stage of the attack, a random name .exe binary is dropped in %APPDATA% in a hidden folder. In our observation, it was EFSUI.EXE as shown in Figure 6. This is detected by majority of the security vendors as referenced from the VirusTotal page.

Fig 6- Cerber ransomeware

Figure 6: Binary extracted from mhtr.jpg detection in VirusTotal

This binary is a NSIS installer that has a list of files that are also dropped in %APPDATA% as shown in Figure 7.

Fig 7- Cerber ransomeware

Figure 7: Files inside the NSIS installer

The manually extracted payload (MD5 – DB073371DCBAC628E69C2B91E1E18BD9) of the Cerber ransomware is present inside the NSIS installer. Figure 8 shows the count of current security vendors from VirusTotal page who detect this binary at the time of writing this blog.

Fig 8 - Cerber Ransomeware

Figure 8: Detection of extracted file from the installer in VirusTotal

Debugging the binary and extracting the configuration provides more insight into how Cerber works, including locations, AV vendors, and file extensions.

In our observation, Cerber doesn’t encrypt files for users in the following countries:

Armenia, Azerbaijan, Belarus, Georgia, Kyrgyzstan, Kazakhstan, Republic of Moldova, Russian Federation, Turkmenistan, Tajikistan, Ukraine and Uzbekistan


It also tries to stop working if it detects the following anti-virus solutions in place:

“av_blacklist”:[“kaspersky lab”,”avast software”,”eset”,”bitdefender”,”bitdefender agent”,”lavasoft”,”arcabit”,”arcavir”,”bullguard ltd”,”bullguard software”,”emsisoft anti-malware”,”escan”,”etrust ez armor”,”ca”,”f-secure”,”g data”,”trustport”]”

Finally, it encrypts files with the following 444 extensions that are likely to be associated with high-value business files:

“Encrypt”:{“files”:[[“.contact”, “.dbx”, “.doc”, “.docx”, “.jnt”, “.jpg”, “.mapimail”, “.msg”, “.oab”, “.ods”, “.pdf”, “.pps”, “.ppsm”, “.ppt”, “.pptm”, “.prf”, “.pst”, “.rar”, “.rtf”, “.txt”, “.wab”, “.xls”, “.xlsx”, “.xml”, “.zip”, “.1cd”, “.3ds”, “.3g2”, “.3gp”, “.7z”, “.7zip”, “.accdb”, “.aoi”, “.asf”, “.asp”, “.aspx”, “.asx”, “.avi”, “.bak”, “.cer”, “.cfg”, “.class”, “.config”, “.css”, “.csv”, “.db”, “.dds”, “.dwg”, “.dxf”, “.flf”, “.flv”, “.html”, “.idx”, “.js”, “.key”, “.kwm”, “.laccdb”, “.ldf”, “.lit”, “.m3u”, “.mbx”, “.md”, “.mdf”, “.mid”, “.mlb”, “.mov”, “.mp3”, “.mp4”, “.mpg”, “.obj”, “.odt”, “.pages”, “.php”, “.psd”, “.pwm”, “.rm”, “.safe”, “.sav”, “.save”, “.sql”, “.srt”, “.swf”, “.thm”, “.vob”, “.wav”, “.wma”, “.wmv”, “.xlsb”, “.3dm”, “.aac”, “.ai”, “.arw”, “.c”, “.cdr”, “.cls”, “.cpi”, “.cpp”, “.cs”, “.db3”, “.docm”, “.dot”, “.dotm”, “.dotx”, “.drw”, “.dxb”, “.eps”, “.fla”, “.flac”, “.fxg”, “.java”, “.m”, “.m4v”, “.max”, “.mdb”, “.pcd”, “.pct”, “.pl”, “.potm”, “.potx”, “.ppam”, “.ppsm”, “.ppsx”, “.pptm”, “.ps”, “.pspimage”, “.r3d”, “.rw2”, “.sldm”, “.sldx”, “.svg”, “.tga”, “.wps”, “.xla”, “.xlam”, “.xlm”, “.xlr”, “.xlsm”, “.xlt”, “.xltm”, “.xltx”, “.xlw”, “.act”, “.adp”, “.al”, “.bkp”, “.blend”, “.cdf”, “.cdx”, “.cgm”, “.cr2”, “.crt”, “.dac”, “.dbf”, “.dcr”, “.ddd”, “.design”, “.dtd”, “.fdb”, “.fff”, “.fpx”, “.h”, “.iif”, “.indd”, “.jpeg”, “.mos”, “.nd”, “.nsd”, “.nsf”, “.nsg”, “.nsh”, “.odc”, “.odp”, “.oil”, “.pas”, “.pat”, “.pef”, “.pfx”, “.ptx”, “.qbb”, “.qbm”, “.sas7bdat”, “.say”, “.st4”, “.st6”, “.stc”, “.sxc”, “.sxw”, “.tlg”, “.wad”, “.xlk”, “.aiff”, “.bin”, “.bmp”, “.cmt”, “.dat”, “.dit”, “.edb”, “.flvv”, “.gif”, “.groups”, “.hdd”, “.hpp”, “.log”, “.m2ts”, “.m4p”, “.mkv”, “.mpeg”, “.ndf”, “.nvram”, “.ogg”, “.ost”, “.pab”, “.pdb”, “.pif”, “.png”, “.qed”, “.qcow”, “.qcow2”, “.rvt”, “.st7”, “.stm”, “.vbox”, “.vdi”, “.vhd”, “.vhdx”, “.vmdk”, “.vmsd”, “.vmx”, “.vmxf”, “.3fr”, “.3pr”, “.ab4”, “.accde”, “.accdr”, “.accdt”, “.ach”, “.acr”, “.adb”, “.ads”, “.agdl”, “.ait”, “.apj”, “.asm”, “.awg”, “.back”, “.backup”, “.backupdb”, “.bank”, “.bay”, “.bdb”, “.bgt”, “.bik”, “.bpw”, “.cdr3”, “.cdr4”, “.cdr5”, “.cdr6”, “.cdrw”, “.ce1”, “.ce2”, “.cib”, “.craw”, “.crw”, “.csh”, “.csl”, “.db_journal”, “.dc2”, “.dcs”, “.ddoc”, “.ddrw”, “.der”, “.des”, “.dgc”, “.djvu”, “.dng”, “.drf”, “.dxg”, “.eml”, “.erbsql”, “.erf”, “.exf”, “.ffd”, “.fh”, “.fhd”, “.gray”, “.grey”, “.gry”, “.hbk”, “.ibank”, “.ibd”, “.ibz”, “.iiq”, “.incpas”, “.jpe”, “.kc2”, “.kdbx”, “.kdc”, “.kpdx”, “.lua”, “.mdc”, “.mef”, “.mfw”, “.mmw”, “.mny”, “.moneywell”, “.mrw”, “.myd”, “.ndd”, “.nef”, “.nk2”, “.nop”, “.nrw”, “.ns2”, “.ns3”, “.ns4”, “.nwb”, “.nx2”, “.nxl”, “.nyf”, “.odb”, “.odf”, “.odg”, “.odm”, “.orf”, “.otg”, “.oth”, “.otp”, “.ots”, “.ott”, “.p12”, “.p7b”, “.p7c”, “.pdd”, “.pem”, “.plus_muhd”, “.plc”, “.pot”, “.pptx”, “.psafe3”, “.py”, “.qba”, “.qbr”, “.qbw”, “.qbx”, “.qby”, “.raf”, “.rat”, “.raw”, “.rdb”, “.rwl”, “.rwz”, “.s3db”, “.sd0”, “.sda”, “.sdf”, “.sqlite”, “.sqlite3”, “.sqlitedb”, “.sr2”, “.srf”, “.srw”, “.st5”, “.st8”, “.std”, “.sti”, “.stw”, “.stx”, “.sxd”, “.sxg”, “.sxi”, “.sxm”, “.tex”, “.wallet”, “.wb2”, “.wpd”, “.x11”, “.x3f”, “.xis”, “.ycbcra”, “.yuv”, “.mab”, “.json”, “.ini”, “.sdb”, “.sqlite-shm”, “.sqlite-wal”, “.msf”, “.jar”, “.cdb”, “.srb”, “.abd”, “.qtb”, “.cfn”, “.info”, “.info_”, “.flb”, “.def”, “.atb”, “.tbn”, “.tbb”, “.tlx”, “.pml”, “.pmo”, “.pnx”, “.pnc”, “.pmi”, “.pmm”, “.lck”, “.pm!”, “.pmr”, “.usr”, “.pnd”, “.pmj”, “.pm”, “.lock”, “.srs”, “.pbf”, “.omg”, “.wmf”, “.sh”, “.war”, “.ascx”, “.tif”, “.k2p”, “.apk”, “.asset”, “.bsa”, “.d3dbsp”, “.das”, “.forge”, “.iwi”, “.lbf”, “.litemod”, “.litesql”, “.ltx”, “.m4a”, “.re4”, “.slm”, “.tiff”, “.upk”, “.xxx”, “.money”, “.cash”, “.private”]]

Encrypted files will have a .cerber extension.

Once files are encrypted, the desktop background changes to that shown in Figure 9.

Fig 9 - Cerber Ransomeware

Figure 9: Desktop background post-Ceber attack

Cerber also drops a VBS file with name “# DECRYPT MY FILES #.vbs,” which plays a message that the files in the system have been encrypted using Microsoft Speech API text-to-speech (TTS). The code is shown below in Figure 10. This message is played 10 times.

Fig 10 - Cerber Ransomeware

Figure 10: Cerber voice message

The ransomware payment page offered for decryption can be accessed with the list of the URLs mentioned in the # DECRYPT MY FILES #.html or # DECRYPT MY FILES #.txt files that are dropped in each of the directories. Options are provided to access the URLs directly or using TOR. The payment page supports 12 languages for providing the decryption and payment assistance.

Fig 11 - Cerber Ransomeware

Fig 11b - Cerber Ransomeware

Figure 11: Cerber ransomware payment page

Ironically, the payment page also uses a “captcha” as a security measure to make sure the page is accessed by a human, as shown in Figure 12.

Fig 11c - Cerber Ransomeware

Figure 12: Cerber captcha

The payment page offers decryption of one file for free. Currently, the payment price is $654 US Dollars, which is valid for five days. After five days, the price is increased to $1,309 US Dollars as shown in Figure 13.

Fig 12 - Cerber Ransomeware

Figure 13: Cerber ransom payment

Detection details

Netskope Advanced Threat Protection will detect the components of this attack as follows:

Initial Word Macro — various filenames
MD5: 624851a23067e014237e8d9869713fd1

NSIS installer — EFSUI.EXE in above
MD5: ee0828a4e4c195d97313bfc7d4b531f1

In order to anticipate and protect against this and other ransomware delivered via cloud apps, we recommend users do the following:

  • Users should disable macros in all Microsoft Office programs. Many are malicious and users should avoid them unless they are very sure that they are benign.
  • Administrators should block macros by default via a group policy. Microsoft has the following TechNet article detailing how to do this.
  • Users should avoid opening untrusted attachments regardless of their extension or filename.
  • Users should always keep their systems and antivirus updated with the latest releases and patches.
  • Administrators should regularly back up critical data in a cloud account and regularly scan cloud files for malware.


I would like to thank Sean Hittel and Ravi Balupari for their assistance on the analysis and reporting.

author image
Ashwin Vamshi
Ashwin Vamshi is a Security Researcher with innate interest in targeted attacks and malwares using cloud services. He is primarily focusing in identifying new attack vectors and malwares, campaigns and threat actors using ‘cloud as an attack vector.’

Stay informed!

Subscribe for the latest from the Netskope Blog