Skeleton key malware gives attackers control of Windows AD controllers

New attack difficullt to spot

Administrators take note, Dell SecureWorks has discovered a clever piece of malware that allows an attacker to authenticate themselves on a Windows Active Directory (AD) server as any user using any password they like once they've broken in using stolen credentials.

It's a hack that would have outwardly subtle but inwardly insidious effects. In a stroke of descriptive genius, Dell's researchers have named the threat 'Skeleton key', which sums up what is going on here.

The description offered by Dell is of a carefully-designed piece of malware meant to do a specific job. The malware is deployed as an in-memory process 'patch' using the compromised admin account for that controller, which makes it harder to spot added to which it generates no network traffic to be picked up by security systems.

The disadvantage is that a reboot of the controller clears the malware from memory, but the attackers can still attempt to reinstate it using a separate compromised workstation or server on the network.

This is no theoretical attack - it was found on a real network and Dell's researchers add:

"CTU researchers have observed a pattern for the injected password that suggests that the threat group has deployed Skeleton Key in multiple organizations."

To emphasise, the attackers can't pull off this attack without first getting their hands on admin credentials for the initial bypass. The interesting question is why, armed with such credentials, they might want to plant something on a controller that replicates this access through other user accounts.

Dell doesn't speculate but it's likely that being able to authenticate on the server using an ordinary user's account, without disrupting normal access from legitimate users, is a way of hiding what the attackers are up to. This implies that the tool is part of a longer-term attack, possibly by a nation state deploying it as part of a larger arsenal of compromises.

"This authentication bypass applies to all services that use single-factor AD authentication, such as web mail and VPNs, and it also allows a threat actor with physical access to a compromised system to unlock the computer by typing the injected password on the keyboard."

Dell has published a list of remediations in its advisory but the biggest of these is simply to protect the admin accounts in the first place using - at the very least - multi-factor authentication. The firm also recommends monitoring Windows Service Control Manager events on AD controllers.

Join the CSO newsletter!

Error: Please check your email address.

Tags DellDell SecureWorkssecurity

More about DellSecureWorks

Show Comments

Featured Whitepapers

Editor's Recommendations

Solution Centres

Stories by John E Dunn

Latest Videos

  • 150x50

    CSO Webinar: Will your data protection strategy be enough when disaster strikes?

    Speakers: - Paul O’Connor, Engagement leader - Performance Audit Group, Victorian Auditor-General’s Office (VAGO) - Nigel Phair, Managing Director, Centre for Internet Safety - Joshua Stenhouse, Technical Evangelist, Zerto - Anthony Caruana, CSO MC & Moderator

    Play Video

  • 150x50

    CSO Webinar: The Human Factor - Your people are your biggest security weakness

    ​Speakers: David Lacey, Researcher and former CISO Royal Mail David Turner - Global Risk Management Expert Mark Guntrip - Group Manager, Email Protection, Proofpoint

    Play Video

  • 150x50

    CSO Webinar: Current ransomware defences are failing – but machine learning can drive a more proactive solution

    Speakers • Ty Miller, Director, Threat Intelligence • Mark Gregory, Leader, Network Engineering Research Group, RMIT • Jeff Lanza, Retired FBI Agent (USA) • Andy Solterbeck, VP Asia Pacific, Cylance • David Braue, CSO MC/Moderator What to expect: ​Hear from industry experts on the local and global ransomware threat landscape. Explore a new approach to dealing with ransomware using machine-learning techniques and by thinking about the problem in a fundamentally different way. Apply techniques for gathering insight into ransomware behaviour and find out what elements must go into a truly effective ransomware defence. Get a first-hand look at how ransomware actually works in practice, and how machine-learning techniques can pick up on its activities long before your employees do.

    Play Video

  • 150x50

    CSO Webinar: Get real about metadata to avoid a false sense of security

    Speakers: • Anthony Caruana – CSO MC and moderator • Ian Farquhar, Worldwide Virtual Security Team Lead, Gigamon • John Lindsay, Former CTO, iiNet • Skeeve Stevens, Futurist, Future Sumo • David Vaile - Vice chair of APF, Co-Convenor of the Cyberspace Law And Policy Community, UNSW Law Faculty This webinar covers: - A 101 on metadata - what it is and how to use it - Insight into a typical attack, what happens and what we would find when looking into the metadata - How to collect metadata, use this to detect attacks and get greater insight into how you can use this to protect your organisation - Learn how much raw data and metadata to retain and how long for - Get a reality check on how you're using your metadata and if this is enough to secure your organisation

    Play Video

  • 150x50

    CSO Webinar: How banking trojans work and how you can stop them

    CSO Webinar: How banking trojans work and how you can stop them Featuring: • John Baird, Director of Global Technology Production, Deutsche Bank • Samantha Macleod, GM Cyber Security, ME Bank • Sherrod DeGrippo, Director of Emerging Threats, Proofpoint (USA)

    Play Video

More videos

Blog Posts

Market Place