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Researcher publishes SignDrop Windows zero-day exploit for SYSTEM access

Public attack code now exists for an unpatched flaw in Windows that lets someone who already has an account on a computer take full control of it. No fix has been reported, so IT teams should watch for Microsoft's response.

Windows privilege escalation zero-day with public exploit
Windows privilege escalation zero-day with public exploit

What's new

Newest coverage

TimelineWhat should my organization do?

What happened

Security researcher Abdelhamid Naceri, who is also known as Nightmare Eclipse, released exploit code for a Windows zero-day (a flaw made public before a fix exists) that he named SignDrop. The exploit can let an attacker gain SYSTEM privileges, the highest level of access on a Windows machine. [1][2]

Security Affairs gives the researcher's other aliases as Chaotic Eclipse and MSNightmare, and describes SignDrop as a local privilege escalation flaw, meaning the attacker must already be able to run code on the computer. [3]

How the exploit works

The proof of concept targets the Common Log File System (CLFS) driver, clfs.sys. The Hacker News reports it abuses a log-authentication feature added to the driver last year, using path redirection when a privileged process opens a prepared log and the driver creates companion files. [4]

SecurityWeek says the technique also involves Windows Defender, triggering arbitrary file creation in the context of the antimalware process. Security Affairs says the flaw sits inside a mitigation Microsoft rolled out and can bypass security protections. [2][3]

What is not yet known

The coverage does not give a CVE identifier, a severity score or a Microsoft advisory for SignDrop, and none of the articles reports attacks in the wild or a patch. Microsoft has not been quoted in the coverage. [1][4][2][3]

Timeline

  1. Further analysis described the exploit as abusing CLFS and Windows Defender. [2][3]

  2. Public proof-of-concept code for a CLFS privilege escalation was described as released earlier in the week. [4]

  3. Researcher Abdelhamid Naceri released the SignDrop exploit code for Windows. [1]

Explained

The technology and terms in this story. Learn more

Business ActionWhat this means inside your organization, and what to do about it, by company size.

Small business

No dedicated security staff; relies on providers

What to know

The flaw needs an attacker who can already run code on a Windows computer, and the sources report no patch yet. [3][4]

What to do

  1. Ask your IT provider whether they are tracking Microsoft's response to SignDrop. [1]
  2. Install Windows updates as Microsoft releases them. [1]

Mid-size company

A small IT or security team

What to know

Public exploit code exists for a local privilege escalation in the CLFS driver; the articles report no fix or workaround. [4][2]

What to do

  1. Watch Microsoft's advisories for a fix or guidance on SignDrop and schedule it once released. [1]
  2. Review which users and systems allow local code execution and limit unnecessary local access. [3]

Large enterprise

A security operations team

What to know

The exploit abuses clfs.sys and Windows Defender behaviour to reach SYSTEM; no indicators or detections have been published in the coverage. [4][2]

What to do

  1. Monitor for Microsoft guidance and for any published detections for SignDrop. [1][3]
  2. Review endpoint telemetry for unexpected activity involving clfs.sys and privileged file creation by the antimalware process. [2]

Sources

  1. [1]BleepingComputer · Nov 12, 16:04 UTC
    New Windows SignDrop zero-day gives hackers SYSTEM privilegescontext
  2. [2]SecurityWeek · Nov 13, 08:50 UTC
    Nightmare Eclipse Drops Windows Zero-Day Exploit ‘SignDrop’context
  3. [3]Security Affairs · Nov 13, 09:02 UTC
    New SignDrop Exploit Can Abuse Windows Defender to Bypass Security Protectionscontext
  4. [4]The Hacker News · Nov 12, 17:50 UTC
    New SignDrop Zero-Day Exploit Turns Windows CLFS Security Feature Into SYSTEM Accesscontext