diff --git a/NuGet.config b/NuGet.config
index dfd4d34..5ccb822 100644
--- a/NuGet.config
+++ b/NuGet.config
@@ -1,10 +1,10 @@
 <?xml version="1.0" encoding="utf-8"?>
 <configuration>
     <packageRestore>
-        <!-- Opts out of both Automatic Package Restore and MSBuild-Integrated Package Restore -->
-        <add key="enabled" value="False" />
-        <!-- Opts out of Automatic Package Restore in Visual Studio -->
-        <add key="automatic" value="False" />
+        <!-- Enable Automatic + MSBuild-Integrated Package Restore -->
+        <add key="enabled" value="True" />
+        <!-- Enable Automatic Package Restore in Visual Studio -->
+        <add key="automatic" value="True" />
     </packageRestore>
     <packageSources>
       <clear />
diff --git a/src/Unic.ErrorManager.Core/Controls/BaseError.cs b/src/Unic.ErrorManager.Core/Controls/BaseError.cs
index 30aea00..a3dfe78 100644
--- a/src/Unic.ErrorManager.Core/Controls/BaseError.cs
+++ b/src/Unic.ErrorManager.Core/Controls/BaseError.cs
@@ -87,16 +87,14 @@ protected string SettingsKey
         /// <param name="e">The <see cref="T:System.EventArgs"/> object that contains the event data.</param>
         protected override void OnLoad(EventArgs e)
         {
-            // if a hostname allow list is defined and the host header value from the request doesn't appear in this list, the rest of this method isn't executed to prevent potential SSRF
-            var hostnameAllowList = Settings.GetSetting(Definitions.Constants.HostnameAllowListSetting);
-            if (!string.IsNullOrWhiteSpace(hostnameAllowList))
+            // validate the host header against allowed hostnames to prevent SSRF via host header injection
+            var requestHost = Request.Headers["host"] ?? string.Empty;
+            var requestHostWithoutPort = requestHost.Split(':')[0];
+            if (!this.IsHostnameAllowed(requestHostWithoutPort))
             {
-                if (!hostnameAllowList.Split(';').Any(h => h.Equals(Request.Headers["host"])))
-                {
-                    this.Response.StatusCode = 403;
-                    this.Response.Write("403 Forbidden");
-                    return;
-                }
+                this.Response.StatusCode = 403;
+                this.Response.Write("403 Forbidden");
+                return;
             }
 
             // add support to all versions of tls
@@ -168,6 +166,16 @@ protected override void OnLoad(EventArgs e)
                 }
             }
 
+            // validate the constructed URL host against allowed hostnames before making the request
+            var constructedUri = new Uri(url.ToString());
+            if (!this.IsHostnameAllowed(constructedUri.Host))
+            {
+                Log.Error($"ErrorManager: Constructed URL host '{constructedUri.Host}' is not allowed. Aborting request.", this);
+                this.Response.StatusCode = 403;
+                this.Response.Write("403 Forbidden");
+                return;
+            }
+
             // parse the page
             HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url.ToString());
 
@@ -190,7 +198,6 @@ protected override void OnLoad(EventArgs e)
             this.HandleBasicAuthentication(request);
             
             HttpWebResponse response = null;
-            bool hasAddedValidationCallback = false;
 
             try
             {
@@ -208,8 +215,7 @@ protected override void OnLoad(EventArgs e)
 
                 if (Settings.GetBoolSetting("ErrorManager.IgnoreInvalidSSLCertificates", false))
                 {
-                    ServicePointManager.ServerCertificateValidationCallback += ValidateRemoteCertificate;
-                    hasAddedValidationCallback = true;
+                    request.ServerCertificateValidationCallback = ValidateRemoteCertificate;
                 }
 
                 // do the request
@@ -224,14 +230,6 @@ protected override void OnLoad(EventArgs e)
 
                 Log.Error($"ErrorManager : {ex.Message}. Request URL: {url}. ", ex, this);
             }
-            finally
-            {
-                // Remove the custom RemoteCertificateValidationCallback due to the global nature of the ServicePointManager
-                if (hasAddedValidationCallback)
-                {
-                    ServicePointManager.ServerCertificateValidationCallback -= ValidateRemoteCertificate;
-                }
-            }
 
             // outputs the page
             if (response != null)
@@ -276,6 +274,47 @@ protected virtual void AddUserAgentHeader(HttpWebRequest request)
             request.UserAgent = userAgent;
         }
 
+        private bool IsHostnameAllowed(string hostname)
+        {
+            if (string.IsNullOrWhiteSpace(hostname)) return false;
+
+            var hostnameAllowList = Settings.GetSetting(Definitions.Constants.HostnameAllowListSetting);
+            var useSitecoreSiteHostnames = Settings.GetBoolSetting(Definitions.Constants.ValidateSitecoreSiteHostnamesSetting, true);
+
+            // check the optional explicit allow list
+            if (!string.IsNullOrWhiteSpace(hostnameAllowList))
+            {
+                if (hostnameAllowList.Split(';').Any(h => h.Equals(hostname, StringComparison.OrdinalIgnoreCase)))
+                {
+                    return true;
+                }
+            }
+
+            // check hostnames from all configured Sitecore sites
+            if (useSitecoreSiteHostnames)
+            {
+                foreach (var siteInfo in SiteContextFactory.Sites)
+                {
+                    if (string.IsNullOrWhiteSpace(siteInfo.HostName)) continue;
+
+                    // SiteInfo.HostName can contain pipe-separated values
+                    var siteHostnames = siteInfo.HostName.Split('|');
+                    if (siteHostnames.Any(h => h.Equals(hostname, StringComparison.OrdinalIgnoreCase)))
+                    {
+                        return true;
+                    }
+
+                    if (!string.IsNullOrWhiteSpace(siteInfo.TargetHostName)
+                        && siteInfo.TargetHostName.Equals(hostname, StringComparison.OrdinalIgnoreCase))
+                    {
+                        return true;
+                    }
+                }
+            }
+
+            return false;
+        }
+
         private void HandleHeaderForwarding(HttpWebRequest request)
         {
             var headers = Settings.GetSetting("ErrorManager.ForwardedHeaders");
diff --git a/src/Unic.ErrorManager.Core/Definitions/Constants.cs b/src/Unic.ErrorManager.Core/Definitions/Constants.cs
index 81d4cd3..18422e8 100644
--- a/src/Unic.ErrorManager.Core/Definitions/Constants.cs
+++ b/src/Unic.ErrorManager.Core/Definitions/Constants.cs
@@ -15,5 +15,7 @@ public static class Constants
         public static string EnableAgentHeaderCheckSetting = "ErrorManager.EnableAgentHeaderCheck";
 
         public static string HostnameAllowListSetting = "ErrorManager.HostnameAllowList";
+
+        public static string ValidateSitecoreSiteHostnamesSetting = "ErrorManager.ValidateSitecoreSiteHostnames";
     }
 }
diff --git a/src/Unic.ErrorManager.Core/Unic.ErrorManager.Core.csproj b/src/Unic.ErrorManager.Core/Unic.ErrorManager.Core.csproj
index e88bd7c..8cc7320 100644
--- a/src/Unic.ErrorManager.Core/Unic.ErrorManager.Core.csproj
+++ b/src/Unic.ErrorManager.Core/Unic.ErrorManager.Core.csproj
@@ -12,7 +12,7 @@
     <AppDesignerFolder>Properties</AppDesignerFolder>
     <RootNamespace>Unic.ErrorManager.Core</RootNamespace>
     <AssemblyName>Unic.ErrorManager.Core</AssemblyName>
-    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
+    <TargetFrameworkVersion>v4.8</TargetFrameworkVersion>
     <FileAlignment>512</FileAlignment>
     <TargetFrameworkProfile />
     <NuGetPackageImportStamp>
diff --git a/src/Unic.ErrorManager.Website/App_Config/Include/01_modules/Unic.ErrorManager.config b/src/Unic.ErrorManager.Website/App_Config/Include/01_modules/Unic.ErrorManager.config
index 6bf0ea4..59939d9 100644
--- a/src/Unic.ErrorManager.Website/App_Config/Include/01_modules/Unic.ErrorManager.config
+++ b/src/Unic.ErrorManager.Website/App_Config/Include/01_modules/Unic.ErrorManager.config
@@ -105,6 +105,25 @@
       -->
       <setting name="NoLicenseUrl" set:value="/sitecore modules/Web/Error Manager/service/nolicense.aspx" />
 
+      <!--  VALIDATE SITECORE SITE HOSTNAMES
+            If true, hostnames configured on Sitecore site definitions (HostName and
+            TargetHostName attributes) are treated as allowed for error page requests.
+            This is the primary SSRF protection mechanism and is enabled by default.
+            Default value: true
+      -->
+      <setting name="ErrorManager.ValidateSitecoreSiteHostnames" value="true" />
+
+      <!--  HOSTNAME ALLOW LIST (OPTIONAL)
+            Semicolon-separated list of additional allowed hostnames for error page
+            requests, checked alongside the Sitecore site hostnames above.
+            Port is not required — the check strips port suffixes automatically.
+            Use this to allow hostnames that are not configured on any Sitecore site
+            definition (e.g. load balancer or CDN hostnames).
+            Example: "cdn.example.com;lb.internal.example.com"
+            Default value: ""
+      -->
+      <setting name="ErrorManager.HostnameAllowList" value="" />
+
       <!-- BOT SEETINGS
            Defines the Bot for the redirect request
       -->
diff --git a/src/Unic.ErrorManager.Website/Unic.ErrorManager.Website.csproj b/src/Unic.ErrorManager.Website/Unic.ErrorManager.Website.csproj
index 1860d7a..e682594 100644
--- a/src/Unic.ErrorManager.Website/Unic.ErrorManager.Website.csproj
+++ b/src/Unic.ErrorManager.Website/Unic.ErrorManager.Website.csproj
@@ -15,7 +15,7 @@
     <AppDesignerFolder>Properties</AppDesignerFolder>
     <RootNamespace>Unic.ErrorManager.Website</RootNamespace>
     <AssemblyName>Unic.ErrorManager.Website</AssemblyName>
-    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
+    <TargetFrameworkVersion>v4.8</TargetFrameworkVersion>
     <UseIISExpress>false</UseIISExpress>
     <FileUpgradeFlags>
     </FileUpgradeFlags>
@@ -68,10 +68,8 @@
     </Reference>
     <Reference Include="System" />
     <Reference Include="System.Data" />
-    <Reference Include="System.Data.DataSetExtensions" />
     <Reference Include="System.Drawing" />
     <Reference Include="System.Web" />
-    <Reference Include="System.Web.Extensions" />
     <Reference Include="System.Xml" />
     <Reference Include="System.Configuration" />
     <Reference Include="System.Web.Services" />
@@ -79,7 +77,6 @@
     <Reference Include="System.Web.DynamicData" />
     <Reference Include="System.Web.Entity" />
     <Reference Include="System.Web.ApplicationServices" />
-    <Reference Include="System.Xml.Linq" />
   </ItemGroup>
   <ItemGroup>
     <Compile Include="Properties\AssemblyInfo.cs" />
@@ -121,6 +118,13 @@
     <Content Include="packages.config" />
     <None Include="Properties\PublishProfiles\LocalDeploy.pubxml" />
     <None Include="Unic.ErrorManager.Website.nuspec" />
+    <Content Include="web.config" />
+    <None Include="web.Debug.config">
+      <DependentUpon>web.config</DependentUpon>
+    </None>
+    <None Include="web.Release.config">
+      <DependentUpon>web.config</DependentUpon>
+    </None>
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Unic.ErrorManager.Core\Unic.ErrorManager.Core.csproj">
diff --git a/src/Unic.ErrorManager.Website/web.Debug.config b/src/Unic.ErrorManager.Website/web.Debug.config
new file mode 100644
index 0000000..fae9cfe
--- /dev/null
+++ b/src/Unic.ErrorManager.Website/web.Debug.config
@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<!-- For more information on using web.config transformation visit https://go.microsoft.com/fwlink/?LinkId=125889 -->
+
+<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
+  <!--
+    In the example below, the "SetAttributes" transform will change the value of 
+    "connectionString" to use "ReleaseSQLServer" only when the "Match" locator 
+    finds an attribute "name" that has a value of "MyDB".
+    
+    <connectionStrings>
+      <add name="MyDB" 
+        connectionString="Data Source=ReleaseSQLServer;Initial Catalog=MyReleaseDB;Integrated Security=True" 
+        xdt:Transform="SetAttributes" xdt:Locator="Match(name)"/>
+    </connectionStrings>
+  -->
+  <system.web>
+    <!--
+      In the example below, the "Replace" transform will replace the entire 
+      <customErrors> section of your web.config file.
+      Note that because there is only one customErrors section under the 
+      <system.web> node, there is no need to use the "xdt:Locator" attribute.
+      
+      <customErrors defaultRedirect="GenericError.htm"
+        mode="RemoteOnly" xdt:Transform="Replace">
+        <error statusCode="500" redirect="InternalError.htm"/>
+      </customErrors>
+    -->
+  </system.web>
+</configuration>
\ No newline at end of file
diff --git a/src/Unic.ErrorManager.Website/web.Release.config b/src/Unic.ErrorManager.Website/web.Release.config
new file mode 100644
index 0000000..da6e960
--- /dev/null
+++ b/src/Unic.ErrorManager.Website/web.Release.config
@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<!-- For more information on using web.config transformation visit https://go.microsoft.com/fwlink/?LinkId=125889 -->
+
+<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
+  <!--
+    In the example below, the "SetAttributes" transform will change the value of 
+    "connectionString" to use "ReleaseSQLServer" only when the "Match" locator 
+    finds an attribute "name" that has a value of "MyDB".
+    
+    <connectionStrings>
+      <add name="MyDB" 
+        connectionString="Data Source=ReleaseSQLServer;Initial Catalog=MyReleaseDB;Integrated Security=True" 
+        xdt:Transform="SetAttributes" xdt:Locator="Match(name)"/>
+    </connectionStrings>
+  -->
+  <system.web>
+    <compilation xdt:Transform="RemoveAttributes(debug)" />
+    <!--
+      In the example below, the "Replace" transform will replace the entire 
+      <customErrors> section of your web.config file.
+      Note that because there is only one customErrors section under the 
+      <system.web> node, there is no need to use the "xdt:Locator" attribute.
+      
+      <customErrors defaultRedirect="GenericError.htm"
+        mode="RemoteOnly" xdt:Transform="Replace">
+        <error statusCode="500" redirect="InternalError.htm"/>
+      </customErrors>
+    -->
+  </system.web>
+</configuration>
\ No newline at end of file
diff --git a/src/Unic.ErrorManager.Website/web.config b/src/Unic.ErrorManager.Website/web.config
new file mode 100644
index 0000000..a3731a0
--- /dev/null
+++ b/src/Unic.ErrorManager.Website/web.config
@@ -0,0 +1,15 @@
+<?xml version="1.0"?>
+<configuration>
+  <!--
+    For a description of web.config changes see http://go.microsoft.com/fwlink/?LinkId=235367.
+
+    The following attributes can be set on the <httpRuntime> tag.
+      <system.Web>
+        <httpRuntime targetFramework="4.8" />
+      </system.Web>
+  -->
+  <system.web>
+    <compilation debug="true" targetFramework="4.8"/>
+    <httpRuntime targetFramework="4.5"/>
+  </system.web>
+</configuration>
\ No newline at end of file