After running SSL Labs tests (ssllabs.com/ssltest), many Windows Server 2008 R2 administrators encounter the frustrating "Grade capped to B due to RC4" warning. Despite following Microsoft's documentation and registry modifications, the cipher suite persists in test results.

Before making changes, verify your current configuration:

# PowerShell command to list enabled cipher suites:
Get-TlsCipherSuite | Format-Table Name, CipherSuite, Cipher, Certificate, Hash

The standard registry modifications require creating these keys under HKLM\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Ciphers:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Ciphers\RC4 128/128]
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Ciphers\RC4 40/128]
"Enabled"=dword:00000000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Ciphers\RC4 56/128]
"Enabled"=dword:00000000

Many administrators overlook the protocol priority configuration. Add this registry entry to ensure proper cipher negotiation:

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Cryptography\Configuration\SSL\00010002]
"Functions"="TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P521,
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P384,
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P256,
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P521,
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P384,
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256,
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA_P521,
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA_P384,
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA_P256,
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA_P521,
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA_P384,
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA_P256,
TLS_RSA_WITH_AES_256_CBC_SHA256,
TLS_RSA_WITH_AES_128_CBC_SHA256,
TLS_RSA_WITH_AES_256_CBC_SHA,
TLS_RSA_WITH_AES_128_CBC_SHA"

For IIS servers, additional steps are required:

# Disable SSLv3 and prioritize modern protocols in IIS
Set-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 3.0\Server' -Name Enabled -Value 0
Set-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Server' -Name Enabled -Value 1

Use these tools to verify RC4 is disabled:

# Nmap command to test SSL/TLS configuration:
nmap --script ssl-enum-ciphers -p 443 yourserver.com

# OpenSSL test command:
openssl s_client -connect yourserver.com:443 -cipher DEFAULT:!RC4

If changes don't appear effective:

1. Ensure all dependent services are restarted (not just IIS)
2. Check for group policies overriding local settings
3. Verify no load balancers or proxies are handling SSL termination
4. Confirm no legacy applications require RC4 compatibility

For administrators preferring GUI tools:

# Download and run IISCrypto (Nartac Software)
# Select "Best Practices" template
# Manually uncheck all RC4 variants
# Apply changes and reboot

While disabling RC4 improves security, be aware that AES cipher suites may increase CPU usage by 10-15% on older hardware. Monitor performance after implementation.

RC4 (Rivest Cipher 4) has been officially deprecated since 2015 due to multiple cryptographic weaknesses. Microsoft Security Advisory 2868725 recommends disabling RC4 entirely in Windows environments. The cipher's vulnerabilities make it susceptible to man-in-the-middle attacks, particularly in TLS implementations.

For Windows Server 2008 R2, you'll need to modify the SCHANNEL registry keys. Here's the complete PowerShell script to disable all RC4 variants:

# Disable RC4 40/128
New-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Ciphers\RC4 40/128" -Name "Enabled" -Value 0 -PropertyType DWORD -Force

# Disable RC4 56/128  
New-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Ciphers\RC4 56/128" -Name "Enabled" -Value 0 -PropertyType DWORD -Force

# Disable RC4 64/128
New-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Ciphers\RC4 64/128" -Name "Enabled" -Value 0 -PropertyType DWORD -Force

# Disable RC4 128/128
New-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Ciphers\RC4 128/128" -Name "Enabled" -Value 0 -PropertyType DWORD -Force

After making registry changes and rebooting, verify using these methods:

Method 1: Using IISCrypto

Download Microsoft's IISCrypto tool (works on Server 2008 R2) and check the cipher suite status.

Method 2: PowerShell Test

[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
$request = [System.Net.WebRequest]::Create("https://yourdomain.com")
try {
    $request.GetResponse() | Out-Null
    Write-Host "RC4 likely disabled - connection succeeded with modern protocols"
} catch {
    Write-Host "Connection failed - verify cipher configurations"
}

If the official Microsoft patch fails to install with "not applicable" error:

1. Verify you're downloading the correct architecture version (x64 for R2)
2. Ensure your server has all prerequisites (check WSUS for missing updates)
3. Try the standalone installer instead of Windows Update

For domain-joined servers, create a Group Policy Object (GPO) with these settings:

Computer Configuration > Policies > Administrative Templates > Network > SSL Configuration Settings > SSL Cipher Suite Order

Set the cipher suite list to exclude all RC4 variants and prioritize AES:
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P256,TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256,TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA_P256,TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA_P256

After implementing changes, test with OpenSSL command:

openssl s_client -connect yourserver.com:443 -cipher RC4

A proper configuration should return "no shared cipher" error, confirming RC4 is disabled.