Linux KVM:  Using Multiple NICs and Routing Traffic Properly Between Them

When setting up a KVM guest to use multiple network interface controllers (NICs), additional ip routes may be needed in order for the additional interfaces to work properly.  For example, if you configure a NIC with a public static IP address and a NIC with an internal private DHCP LAN IP address, you must create a route for any traffic that comes through the DHCP LAN IP address to respond via the interface from which the request originated.  Otherwise, forwarded NAT traffic from the main KVM host to the DHCP internal LAN IP will reach its destination, but no response will be sent back (because it will attempt to send the response via the configured static IP address interface which may NOT be the original destination of the senders request).

The Solution:

https://unix.stackexchange.com/questions/4420/reply-on-same-interface-as-incoming/23345#answer-23345

From the above link, the solution for me was to do the following in the KVM guest virtual machine:

Only needs to be done once:

sudo -i
echo 200 isp1 >> /etc/iproute2/rt_tables

Setting up the route (adjust variables as necessary):

sudo -i
ip rule add from <interface_IP> table isp1 priority 900
ip rule add from <interface_IP> dev <interface> table isp1
ip route add default via <gateway_IP> dev <interface> table isp

The command I used for my specific setup:

sudo -i
ip rule add from 192.168.122.10 table isp1 priority 900 
ip rule add from 192.168.122.10 dev ens9 table isp1 
ip route add default via 192.168.122.1 dev ens9 table isp1

Making it permanent (apply on system start up):

sudo -i
nano /etc/network/interfaces

I added the below post-up rules (adjust variables as necessary):

auto ens9
iface ens9 inet dhcp
        post-up ip rule add from <interface_IP> table isp1 priority 900
        post-up ip rule add from <interface_IP> dev <interface> table isp1
        post-up ip route add default via <gateway_IP> dev <interface> table isp1

The route is created whenever the dhcp interface is brought up.

Obtaining Let's Encrypt HTTP Validation Server IP Addresses

Use your webserver logs:

sudo apt-get install john
cat access_log.1 | grep "Let's Encrypt" | awk '{print $1}' | unique ips
cat ips

Recreating a Lost or Removed EFI Windows Boot Partition

In case you remove an SSD with a Windows Boot Partition that boots an installation of Windows, you'll need to recreate the boot system to be able to successfully boot again.  To recreate the boot EFI partition on another drive or partition, perform the following:

1) Create or use an existing Windows installation disc or flash drive (you can use Rufus USB to format a flash drive with a Windows ISO)
2) Boot PC using your Windows installation media (a CD, DVD, flash drive, etc containing Windows installation files)
3) Press SHIFT + F10 on the first screen to bring up Command Prompt
4) Run the following commands and click Enter each time at Command Prompt:

diskpart
list disk
select disk N (N refers to the disk which contains the deleted the EFI System partition)
list partition
create partition efi size=200
format quick fs=fat32
list partition
list volume (find the volume letter which belongs to the installed Windows OS)
exit (exit diskpart)
bcdboot M:\windows (M refers to the volume letter of installed Windows OS)

Add any additional Windows installations by repeating the bcdboot command followed by the installation path for any other Windows installations you want added to the menu.  For example, I added my Windows 7 partition using the below command:

bcdboot P:\windows

You should now be able to boot Windows again without needing the old boot partition or drive.

Instructions were modified from this post.

Ryzen Windows 10 Random BSOD Fix

For the longest time, I could not figure out why I couldn't get Windows 10 to consistently install or run in a stable fashion for longer than a few minutes on my Ryzen 1700X or my Ryzen 3900X AMD CPU. 

After trying everything I could think of and pulling my hair out, I found a simple solution that appears to have worked!  Simply disable Link State Power Management in your Power Setting's active power plan.

Go to the "Control Panel" -> "Power Options" -> Click on the "Change plan settings" link for your selected power plan -> click on the "Change advanced power settings" link -> navigate to the "PCI Express" category -> find the "Link State Power Management" option -> set it to "Off" (for both on battery and plugged in).

In general, there are several reasons why a computer can suffer a catastrophic Blue Screen of Death (BSOD) issue, but in my case, it turns out I just needed to adjust some power settings to compensate for a storage controller bug found in some solid state hard drives.  Thanks Reddit users for helping me find the fix!

https://www.reddit.com/r/Amd/comments/cx3rpb/new_system_with_ryzen_and_windows_10_freezes/#t1_eykk63l

Run Everything as an Administrator in Windows 10 by Default – Same Windows 7 Behavior

To run everything as an administrator in Windows 10, there are several settings that must be changed.  In Windows 7, you would only have to disable UAC for the current user:

This isn't good enough in Windows 10.  You have to disable UAC for the current user AND do the following:

Run gpedit.msc to open the Local Group Policy Editor. Expand Computer Configuration, Windows Settings, Security Settings, Local Policies, and Security Options. Four settings need to be updated:

1. Set "User Account Control: Behavior of the elevation prompt for administrators in Admin Approval Mode" to Elevate without prompting.
2. Set "User Account Control: Detect application installations and prompt for elevation" to Disabled.
3. Set "User Account Control: Run all administrators in Admin Approval Mode" to Disabled.
4. Set "User Account Control: Only elevate UIAccess applications that are installed in secure locations" to Disabled.

The LGPE automatically saves all changes, so exit it and reboot.

Please read more here:

https://superuser.com/questions/1002262/run-applications-as-administrator-by-default-in-windows-10

Common Internet File System (CIFS) – Login Using Anonymous (Guest) Account to Network Shares & NAS Systems

Windows 7:

To map and connect to a network share that is using the SMB1 protocol in Windows, there are a few things that you need to do depending on which version of Windows you use.  In Windows 7, it should be pretty easy.  When mapping the network drive, be sure to check the "Connect using different credentials" box.  For the login, use "anonymous".  Leave the password field blank (don't provide a password).

Windows 10:

Windows 10 doesn't support the SMB1 protocol by default.  However, it can be enabled.  To enable SMB1 support, go to the Control Panel, click on "Programs and Features", and then click on the "Turn Windows features on or off" link in the left sidebar.  Under the "SMB 1.0" category, enable the "SMB 1.0/CIFS Client" by clicking the checkbox and making sure it's in a checked state.  Uncheck the "SMB 1.0/CIFS Automatic Removal" entry if it's enabled as it will cause anonymous logins to SMB1.0 shares to fail.

The next step is to configure Windows 10 to allow anonymous logins to network shares.

To enable access under the guest account from your computer, you need to use the Group Policy Editor (gpedit.msc). Go to the section: Computer Configuration -> Administrative templates -> Network -> Lanman Workstation. Find and enable the policy "Enable insecure guest logons". These policy settings determine whether the SMB client will allow the guest logon to the SMB server.

More Detailed Guide | Archived Copy

Windows 7 and 10:

If you get a message that a drive is already mapped using different credentials, simply map the connection using its IP address instead rather than its name. 

Destroy Windows Spying

Destroy Windows Spying is a great little utility that stops Microsoft from collecting some telemetry without your permission on Windows 7 and Windows 10.  It is an open source project hosted on GitHub.

Download and use Destroy Windows Spying for both Windows 7 and Windows 10. 

After you run Destroy Windows Spying, Skype may not work due to an overly aggressive hosts file entry.   To fix it, remove the following entry from the C:\Windows\System32\drivers\etc\hosts file:

client-s.gateway.messenger.live.com

Installing Chrome WebDriver (Linux Script)

Find out which version of Chrome is installed on your system before running the below commands.  You can find out your chrome version by running the following command:

google-chrome --version

Adjust the version number (replace {VERSION_NUMBER})  in the below commands to match the version installed on your system!!!

sudo -i
cd ~/Downloads
rm chromedriver_linux64.zip
wget -N https://chromedriver.storage.googleapis.com/{VERSION_NUMBER}/chromedriver_linux64.zip
unzip chromedriver_linux64.zip
mv chromedriver /usr/bin/chromedriver
chown root:root /usr/bin/chromedriver
chmod +x /usr/bin/chromedriver

Selenium and other libraries that rely on the Chrome WebDriver should now work properly.

ASP.NET MVC – The Smart Way to Prevent Cross-Site Request Forgery (CSRF) Attempts

WebAPI (AJAX XHR) and Normal POST Operations

If your ASP.NET MVC application uses some WebAPI endpoints which are called using XHR (AJAX) requests from clientside JavaScript, you can still protect against CSRF attacks by validating the origin of such a request (when it is an AJAX request) or perform the default action of validating the anti-CSRF token (for POST form requests).

I modified the below code from https://stackoverflow.com/questions/35085507/set-validateantiforgerytoken-attribute-to-get-post-for-same-action-mvc5#answer-35085970 or ARCHIVE

using System.ComponentModel;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Web.Helpers;
using System.Linq;
using System.Collections.Generic;
using System.Configuration;
namespace System.Web.Mvc
{
    /// <summary>
    /// Cross-Site Request Forgery (CSRF) Prevention Filter for WebAPI and Normal MVC Controllers
    /// Normal POST operations = token is checked
    /// Normal controller GET operations = ignored
    /// WebAPI requests = check to make sure they were initiated by an AJAX request from a trusted origin
    /// </summary>    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = false, Inherited = true)]
    public sealed class ValidateAntiForgeryTokenPOSTOrAJAXOrigin : FilterAttribute, IAuthorizationFilter
    {
        private string _salt;        

        public ValidateAntiForgeryTokenAttribute2() : this(AntiForgery.Validate)
        {
        }        

        internal ValidateAntiForgeryTokenAttribute2(Action validateAction)
        {
            Debug.Assert(validateAction != null);
            ValidateAction = validateAction;
        }
        
        [SuppressMessage("Microsoft.Naming", "CA2204:Literals should be spelled correctly", MessageId = "AdditionalDataProvider", Justification = "API name.")]
        [SuppressMessage("Microsoft.Naming", "CA2204:Literals should be spelled correctly", MessageId = "AntiForgeryConfig", Justification = "API name.")]
        [Obsolete("The 'Salt' property is deprecated. To specify custom data to be embedded within the token, use the static AntiForgeryConfig.AdditionalDataProvider property.", error: true)]
        [EditorBrowsable(EditorBrowsableState.Never)]
        
        public string Salt
        {
            get { return _salt; }
            set
            {
                if (!String.IsNullOrEmpty(value))
                {
                    throw new NotSupportedException("The 'Salt' property is deprecated. To specify custom data to be embedded within the token, use the static AntiForgeryConfig.AdditionalDataProvider property.");
                }
                _salt = value;
            }
        }

        internal Action ValidateAction { get; private set; }        
        
        public void OnAuthorization(AuthorizationContext filterContext)
        {
            string validOrigins = ConfigurationManager.AppSettings["AllowedEnvironments"]; // Example in web.config <add key="AllowedEnvironments" value="https://testurl.com:4443,https://testurl.com,https://testurl2.com" />
            bool skipCheck = false;
            
            if(ConfigurationManager.AppSettings["LocalDevMode"] == "1")
            {
                skipCheck = true;
            }
            
            // In AJAX requests, the origin header is always sent (UNLESS IT'S COMING FROM THE SAME ORIGIN), so we can validate that it comes from a trusted location to prevent CSRF attacks - but if one isn't sent, we won't do anything (assume trusted)
            // In which case, we don't need to do any token checking either 🙂
            if(!skipCheck && !string.IsNullOrEmpty(validOrigins))
            {
                List<string> validOriginURLs = validOrigins.Split(',').ToList();
                if(filterContext.HttpContext.Request.Headers["Origin"] != null && !string.IsNullOrEmpty(filterContext.HttpContext.Request.Headers["Origin"].ToString()))
                {
                    string origin = filterContext.HttpContext.Request.Headers["Origin"];
                    if(!validOriginURLs.Contains(origin))
                    {
                        filterContext.Result = new RedirectResult("~/Home/InvalidRequest");
                        skipCheck = true; // Still set to true to prevent additional validation
                    }
                    else
                    {
                        skipCheck = true;
                    }
                }
            }
        
            if(!skipCheck){
                var request = filterContext.HttpContext.Request.HttpMethod;
                if (request != "GET" && (!filterContext.HttpContext.Request.IsAjaxRequest() || (filterContext.HttpContext.Request.IsAjaxRequest() && (filterContext.HttpContext.Request.Headers["X-Request-With"] == null || filterContext.HttpContext.Request.Headers["X-Requested-With"] != "XMLHttpRequest"))))
                {
                    // Do normal form POST antiforgery token check
                    if (filterContext == null)
                    {
                        throw new ArgumentNullException("filterContext");
                    }                    try
                    {
                        ValidateAction();
                    }
                    catch(Exception e)
                    {
                        filterContext.Result = new RedirectResult("~/Home/InvalidRequest");
                    }
                }
            }
        }
    }
}

ASP.NET Web API – Accessing Session Information

If WebAPI needs access to SESSION information, here's how to do it:

https://stackoverflow.com/questions/9594229/accessing-session-using-asp-net-web-api#answer-17539008 or ARCHIVE