Threat Signal Report

Unpatched Windows Elevation of Privilege Vulnerability (CVE-2021-36934) Disclosed to the Public

Description

On July 20th, 2021, Carnegie Mellon University's CERT Coordination Center publicly disclosed information on an un-patched Windows Elevation of Privilege Vulnerability (CVE-2021-36934), also known as SeriousSAM or HiveNightmare, to the public.

This vulnerability arises from non-administrative users having access to Security Accounts Manager (SAM), SYSTEM, and SECURITY registry hive files. Upon successful exploitation of the vulnerability, an attack will be able to run run arbitrary code with SYSTEM privileges.

At this time, Microsoft has acknowledged the vulnerability, however has not released a patch.


How Serious of an Issue is This?

MEDIUM. While an attacker will be able to run run arbitrary code with SYSTEM privileges upon successful exploitation, the attacker must have the ability to execute exploit code on a victim system.


How Widespread is this Attack?

At this time, we are not aware of report or indication that CVE-2021-36934 is being exploited in the wild.


Has the Vendor Released an Advisory for the Vulnerability?

Yes. Microsoft has released an advisory for CVE-2021-36934.


Are Patches Available for Reported Vulnerabilities by the Vendor?

No, Microsoft has not released a patch for the vulnerability.


Which Version of Windows are Vulnerable?

Not all versions of Windows are affected. The Microsoft advisory states "we can confirm that this issue affects Windows 10 version 1809 and newer operating systems".


What is the Status of Coverage?

FortiGuard Labs has added the following Anti-Virus (AV) detection based on available Proof-of-Concept code:


Riskware/ProofConceptShadowSteal


Any Other Suggested Mitigation?

In their advisory, Microsoft has provided the following as workarounds:


Restrict access to the contents of %windir%\system32\config

  1. Open Command Prompt or Windows PowerShell as an administrator.
  2. Run this command: icacls %windir%\system32\config\*.* /inheritance:e

Delete Volume Shadow Copy Service (VSS) shadow copies

  1. Delete any System Restore points and Shadow volumes that existed prior to restricting access to %windir%\system32\config.
  2. Create a new System Restore point (if desired).

Impact of workaround Deleting shadow copies could impact restore operations, including the ability to restore data with third-party backup applications.

Note You must restrict access and delete shadow copies to prevent exploitation of this vulnerability.


Definitions

Traffic Light Protocol

Color When Should it Be used? How may it be shared?

TLP: RED

Not for disclosure, restricted to participants only.
Sources may use TLP:RED when information cannot be effectively acted upon by additional parties, and could lead to impacts on a party's privacy, reputation, or operations if misused. Recipients may not share TLP:RED information with any parties outside of the specific exchange, meeting, or conversation in which it was originally disclosed. In the context of a meeting, for example, TLP:RED information is limited to those present at the meeting. In most circumstances, TLP:RED should be exchanged verbally or in person.

TLP: AMBER

Limited disclosure, restricted to participants’ organizations.
Sources may use TLP:AMBER when information requires support to be effectively acted upon, yet carries risks to privacy, reputation, or operations if shared outside of the organizations involved. Recipients may only share TLP:AMBER information with members of their own organization, and with clients or customers who need to know the information to protect themselves or prevent further harm. Sources are at liberty to specify additional intended limits of the sharing: these must be adhered to.

TLP: GREEN

Limited disclosure, restricted to the community.
Sources may use TLP:GREEN when information is useful for the awareness of all participating organizations as well as with peers within the broader community or sector. Recipients may share TLP:GREEN information with peers and partner organizations within their sector or community, but not via publicly accessible channels. Information in this category can be circulated widely within a particular community. TLP:GREEN information may not be released outside of the community.

TLP: WHITE

Disclosure is not limited.
Sources may use TLP:WHITE when information carries minimal or no foreseeable risk of misuse, in accordance with applicable rules and procedures for public release. Subject to standard copyright rules, TLP:WHITE information may be distributed without restriction.