Accelerate your SSE journey. Join Netskope at RSA.

  • Security Service Edge Products

    Protect against advanced and cloud-enabled threats and safeguard data across all vectors.

  • Borderless SD-WAN

    Confidently provide secure, high-performance access to every remote user, device, site, and cloud.

  • Platform

    Unrivaled visibility and real-time data and threat protection on the world's largest security private cloud.

Netskope Named a Leader in the 2022 Gartner Magic Quadrant™ for SSE Report

Get the report Go to Products Overview
Netskope gartner mq 2022 sse leader
Gartner® Quick Answer: How Does Netskope’s Acquisition of Infiot Impact SD-WAN, SASE, and SSE Projects?

Get the report
Gartner quick answer
Netskope delivers a modern cloud security stack, with unified capabilities for data and threat protection, plus secure private access.

Explore our platform
Birds eye view metropolitan city
Make the move to market-leading cloud security services with minimal latency and high reliability.

Learn more
Lighted highway through mountainside switchbacks
Prevent threats that often evade other security solutions using a single-pass SSE framework.

Learn more
Lighting storm over metropolitan area
Zero trust solutions for SSE and SASE deployments

Learn more
Boat driving through open sea
Netskope enables a safe, cloud-smart, and fast journey to adopt cloud services, apps, and public cloud infrastructure.

Learn more
Wind turbines along cliffside
  • Our Customers

    Netskope serves more than 2,000 customers worldwide including more than 25 of the Fortune 100

  • Customer Solutions

    We are here for you and with you every step of the way, ensuring your success with Netskope.

  • Training and Certification

    Netskope training will help you become a cloud security expert.

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 more
Netskope Professional Services
Secure your digital transformation journey and make the most of your cloud, web, and private applications with Netskope training.

Learn more
Group of young professionals working
  • Resources

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

  • Blog

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

  • Events & Workshops

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

  • Security Defined

    Everything you need to know in our cybersecurity encyclopedia.

Security Visionaries Podcast

Episode 10: Building Security Relationships Through Transparency
In this episode, Mike and Andreas discuss aligning with works councils, forging business relationships through transparency, and embedding security into value streams.

Play the podcast
Building Security Relationships Through Transparency
Read the latest on how Netskope can enable the Zero Trust and SASE journey through security service edge (SSE) capabilities.

Read the blog
Sunrise and cloudy sky
Netskope at RSA

Join Netskope at RSA Conference this year and be part of the real conversations on SASE and Zero Trust. Stop by our booth in South Hall, chat with an expert, register for our speaking sessions, and unwind by joining us at one of our events!

Learn more
RSA logo
What is Security Service Edge?

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

Learn more
Four-way roundabout
  • Company

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

  • Why Netskope

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

  • Leadership

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

  • Partners

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

Netskope enables the future of work.

Find out more
Curvy road through wooded area
Netskope is redefining cloud, data, and network security to help organizations apply Zero Trust principles to protect data.

Learn more
Switchback road atop a cliffside
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 more
Group of diverse young professionals smiling

SLUB’s the Word: Covert CnC over Slack

May 08 2019
Tags
Netskope Threat Research Labs
Slack Security

In this post, we provide details of the SLUB backdoor, how it uses SaaS apps including Slack as a command and control channel, and how CASB controls can prevent this and similar threats from affecting the enterprise. For traditional firewalls and even for next-gen firewalls and intrusion detection/prevention systems, attacks like these are extremely insidious since they leverage allow listed services in a malicious way. Many enterprises use Slack day-to-day, and so an attack using a “known good” service may go undetected.

What is SLUB?

SLUB (SLack and GitHUB) is a backdoor, discovered and reported on by Cedric Pernet, Daniel Lunghi, Jaromir Horejsi, and Joseph C. Chen at Trend Micro. The malware was spread via a watering hole attack which exploited CVE-2018-8174. A downloader then retrieved the SLUB backdoor and executed it by exploiting CVE-2015-1701, a vulnerability in the Windows operating system which provided SYSTEM-level privileges. Trend concluded that this was likely the work of an advanced persistent threat actor due to the sophistication of both the attack vector and the malware.

The malware is notable for its ability to evade traditional network intrusion detection systems by leveraging common SaaS applications such as Slack, Github, and File.io.

What are its capabilities?

The SLUB backdoor maintains persistence by setting a registry key named “Microsoft Setup Initializazion” (yes, the spelling of initialization is incorrect in the file) in SOFTWARE\Microsoft\Windows\CurrentVersion\Run, naming itself “Windows-RT-KB2937636.dll”. It uses the rundll32 application to execute the main program logic, which is contained in the “UpdateMPUnits” function.

The malware has a suite of functions that are run based on the contents of a GitHub gist which it retrieves through use of the statically-linked Curl library. It then uses the Boost library (also statically linked) to parse the commands from the Github gist.

When the malware “wakes up”, it will make its initial call out to an attacker-controlled Slack workspace with the victim’s computer name and username. This same Slack workspace is used for posting the responses and results of every command received via the Github gist, using Curl and the statically-linked JsonCpp library. This is a critical channel for the attacker since it gives them a pulse on the infected machines, allowing them to keep inventory, have an idea of whether or not their commands are successful, and when querying for information, Slack is the lifeline which provides it back to them.

File uploads also rely on the curl library and are sent to an attacker-controlled bucket on file.io.

Figure 1 – disassembly showing Slack token.

exec – Execute instruction

Leverages cmd.exe to run instructions on the target system. It will write a log file of the format “%ws\%u_cmd_out.tmp” during execution where output is written, as well as a similarly named .dat file in some cases. The files are deleted at the end of the command execution and a message indicating success or failure is posted to the attacker’s Slack workspace.

dnexec – Download and execute

Here, a file is downloaded and executed using CreateProcessW. If the process fails to run or once the thread has completed execution, the file is deleted and a message is posted to the attacker’s Slack workspace.

update – Download a file, run it, and delete the old file

This functionality “updates” a file, by downloading a new attacker-specified file, deleting the old version, and running the new file. A message indicating completion or failure is posted to the attacker’s Slack workspace.

destroy – Cover your tracks

When SLUB receives the destroy command, it will move to cover its tracks. Through a series of commands, it will remove any trace of itself from the user’s system, deleting the registry key and the dll that serves as the main program logic. When initiated, a message is posted in the Slack workspace identifying the machine and user which will have the malware deleted.

file – Exfiltrate files

This is the main use of File.io and one of the noteworthy uses of Slack in the SLUB backdoor. The files are uploaded to File.io via Curl and the REST API. In an effort to evade traditional IDS/IPS, SLUB uses Curl to interact with the Slack “postMessages” API and an embedded token to conduct file operations, sending the file link to one of a number of channels (“dailynews” and “fallback” are two of the embedded channel names) in the same attacker-controlled workspace.

capture – Screen capture

The Capture feature of the SLUB backdoor will capture an image of the current screen or of the active window. The screenshot is uploaded to file.io and a link to the file is posted in the Slack workspace.

dir – Directory operations

Directory operations creates, moves, and deletes specified directories from the victim system. Upon completion or failure, the directory name and status are posted to the attacker’s Slack workspace.

proc – Process operations

The process operations suite of commands allows for the listing and termination of Processes. For listing, the list of processes along with the victim’s computer name are posted to the attacker’s Slack workspace. For termination, the success or failure is posted to the attacker’s Slack workspace.

drive – Drive operations

Collects information about the victim’s drive including listing files, collecting sevice ID, aerial number, free space, total size, volume name, journal info, drive type, whether or not encryption is used, and extended attributes. All of this information, along with the victim’s computer name are posted to Slack upon successful completion of the operation.

reg – Registry operations

Interestingly – SLUB features several registry operations. This is notable since many times, malware either does not include this functionality, or it is not explicitly available as a command, since it could be accessed through something like the exec command. In this case, the malware authors very specifically implemented methods to interact with the registry. The reg command set maps out the registry and provides attackers the option to query, modify, read, and write arbitrary registry entries. Success or failure status are posted to the attacker’s Slack workspace.

tmout – Sleep

Tmout will put the malware to sleep for some attacker-provided number of seconds.

Conclusion

As Trend Micro noted in their reporting on this same malware, the use of multiple cloud services by a single piece of malware is unique, but based on the cloud use cases that we at Netskope are familiar with, we expect this trend to grow, particularly since traditional, non-CASB methods used for defending networks are ineffective against these attacks. So far, we have not seen any SLUB samples other than the one that was investigated by Trend Micro, and continue to monitor our telemetry for similar command and control vectors.

As attackers evolve, they will continue to find new ways to evade the detections that their would-be victims put in place. Detecting these evasions will prove difficult for traditional network-based methods and will instead require application-layer detections and use of machine learning techniques to prevent. Netskope can mitigate the use of Slack as a command and control channel via our CASB solution which detects connections to unsanctioned workspaces. Our machine learning and anomaly detection system can also flag unusual use of SaaS services. Abuse of SaaS applications in this way will continue to be of interest to the Netskope Threat Research Labs. As we find new or similar samples, we will report them here on the Netskope blog.

General Recommendations

  • Always keep browsers fully patched and up-to-date. Watering hole attacks are notoriously difficult to mitigate, especially for unpatched or out-of-date browsers.
  • Detect and remediate cloud threats using a threat-aware CASB solution like Netskope and enforce policy on usage of unsanctioned services as well as unsanctioned instances of sanctioned cloud services

Netskope Detection

If a connection to an unauthorized Slack workspace is attempted by the malware, Netskope can alert you or block the connection entirely through the use of the inline CASB connector. If the session is blocked or an alert is generated, information about the attempt will be found in the SkopeIT application events.

Figure 2 SkopeIT event