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RDP Bug Takes New Approach to Host Compromise
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tdsan
tdsan,
User Rank: Ninja
7/19/2019 | 5:30:27 PM
Authenticated user, hard to defend against that
The remote code execution bug is in Remote Desktop Services, formerly known as Terminal Services, when an authenticated attacker abuses clipboard redirection.

We have identified ways to address this issue.
# Identify Administrators users
$users = New-Object -TypeName System.Security.Principal.NTAccount ("Administrators")

# Security Principles for users accessing systems
$SIDofSecureUserGroup = $users.Translate([System.Security.Principal.SecurityIdentifier]).Value

# Secure User Groups found in the Administrators Group
$SecureMachineGroupSDDL = "D:(A;;CC;;; $SIDofSecureUserGroup)"

# Remote Desktop DisplayName for individual rules
$rule = (Get-NetFirewallRule -DisplayName "Remote Desktop*").DisplayName
    foreach ($i in $rule) {
        Set-NetFirewallRule -DisplayName $i -Profile "Private"
    }

# Set Remote Desktop, add Builtin\Administrators groups to the filter
$nfSecurityFilter = Get-NetFirewallRule -DisplayName "Remote Desktop*" | Get-NetFirewallSecurityFilter

# Set NetFirewallSecurity Filter Settings for Authorized Users, login required for local users
Set-NetFirewallSecurityFilter -RemoteMachine $SecureMachineGroupSDDL -InputObject $nfSecurityFilter -Authentication Required -Encryption Required

#This cmdlet can be run using only the pipeline.
foreach ($i in $rule) {
    Get-NetFirewallRule -DisplayName $i | Get-NetFirewallSecurityFilter | Set-NetFirewallSecurityFilter -RemoteMachine $SecureMachineGroupSDDL -Authentication Required -Encryption Required
}

#Looks for Remote Desktop rule, then sends the results to a file on your desktop call fwrules.txt (append)

Get-NetFirewallRule -DisplayName "Remote Desktop*" | out-file $env:USERPROFILE\desktop\fwrules.txt -Append
Get-NetFirewallRule -DisplayName "Remote Desktop*" | Get-NetFirewallSecurityFilter | out-file $env:USERPROFILE\desktop\fwfilter.txt -Append

We have implemented this fix on our site, maybe someone from the various teams could utilize this code to ensure RDP is not compomised.

Todd
miha12
miha12,
User Rank: Apprentice
7/20/2019 | 7:36:40 AM
nice post
Amazing work
tdsan
tdsan,
User Rank: Ninja
7/22/2019 | 11:59:46 PM
Re: nice post
Also, one thing about Hyper-V, if we apply the same rules to the Hyper-V environment, we can isolate Hyper-V's use to the localsubnet so no-one outside of the network could access those servers. It could be locked down even further using Encryption and Authentication.

Todd


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