Microsoft Windows: Multiple vulnerabilities

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                         ZMCIRT Vulnerability Bulletin

                             ZMC-2021.07.21.0850
                Microsoft Windows: Multiple vulnerabilities
                               21st July 2021

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Product:          Microsoft Windows
Operating System: Windows
Impact/Access:    Execute Arbitrary Code/Commands -- Existing Account
                  Administrator Compromise        -- Existing Account
Resolution:       Mitigation
CVE Names:        CVE-2021-36934  

OVERVIEW

        Microsoft has released an out of band advisory for a Windows 
        elevation of privilege vulnerability. Microsoft has assigned 
        CVE-2021-36934 to this vulnerability [1]


IMPACT

        Microsoft states that "An elevation of privilege vulnerability 
        exists because of overly permissive Access Control Lists (ACLs) on 
        multiple system files, including the Security Accounts Manager (SAM)
        database. An attacker who successfully exploited this vulnerability
        could run arbitrary code with SYSTEM privileges. An attacker could 
        then install programs; view, change, or delete data; or create new 
        accounts with full user rights.
        
        An attacker must have the ability to execute code on a victim system
        to exploit this vulnerability." [1]
        
        Microsoft currently advises that this issue affects Windows 10 
        versions 1809 and newer. [1]


MITIGATION

        There is currently no patch available for this vulnerability, 
        Microsoft have provided the following workaround:
        "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." [1]
        
        Microsoft will update the CVE as their investigation progresses. [1]


REFERENCES

        [1] Windows Elevation of Privilege Vulnerability
            https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-36934


 
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