diff --git a/QuickLook/Helpers/ExtensionFilterHelper.cs b/QuickLook/Helpers/ExtensionFilterHelper.cs
new file mode 100644
index 000000000..0027e2919
--- /dev/null
+++ b/QuickLook/Helpers/ExtensionFilterHelper.cs
@@ -0,0 +1,198 @@
+// Copyright © 2017-2025 QL-Win Contributors
+//
+// This file is part of QuickLook program.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+using QuickLook.Common.Helpers;
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+
+namespace QuickLook.Helpers;
+
+/// <summary>
+/// Helper class for managing file extension allowlist/blocklist filtering.
+/// <para>
+/// <b>Blocklist mode (default):</b> All extensions are allowed except those in the blocklist.
+/// If the blocklist is empty, all files are allowed.
+/// </para>
+/// <para>
+/// <b>Allowlist mode:</b> Only extensions in the allowlist can be previewed.
+/// If the allowlist is empty in allowlist mode, all files are allowed (no filtering).
+/// </para>
+/// <para>
+/// Directories and files without extensions are always allowed regardless of the mode.
+/// </para>
+/// </summary>
+public static class ExtensionFilterHelper
+{
+    private const string AllowlistKey = "ExtensionAllowlist";
+    private const string BlocklistKey = "ExtensionBlocklist";
+    private const string UseAllowlistModeKey = "UseExtensionAllowlistMode";
+    private static readonly char[] ExtensionSeparators = [';', ','];
+
+    private static HashSet<string> _allowlistCache;
+    private static HashSet<string> _blocklistCache;
+    private static bool? _useAllowlistModeCache;
+
+    /// <summary>
+    /// Gets or sets whether to use allowlist mode.
+    /// When true, only extensions in the allowlist can be previewed.
+    /// When false (default), extensions in the blocklist are blocked from preview.
+    /// </summary>
+    public static bool UseAllowlistMode
+    {
+        get
+        {
+            _useAllowlistModeCache ??= SettingHelper.Get(UseAllowlistModeKey, false);
+            return _useAllowlistModeCache.Value;
+        }
+        set
+        {
+            _useAllowlistModeCache = value;
+            SettingHelper.Set(UseAllowlistModeKey, value);
+        }
+    }
+
+    /// <summary>
+    /// Gets the current allowlist of file extensions.
+    /// Extensions should be in the format ".ext" (with leading dot).
+    /// </summary>
+    public static HashSet<string> Allowlist
+    {
+        get
+        {
+            if (_allowlistCache == null)
+            {
+                var list = SettingHelper.Get(AllowlistKey, string.Empty);
+                _allowlistCache = ParseExtensionList(list);
+            }
+            return _allowlistCache;
+        }
+    }
+
+    /// <summary>
+    /// Gets the current blocklist of file extensions.
+    /// Extensions should be in the format ".ext" (with leading dot).
+    /// </summary>
+    public static HashSet<string> Blocklist
+    {
+        get
+        {
+            if (_blocklistCache == null)
+            {
+                var list = SettingHelper.Get(BlocklistKey, string.Empty);
+                _blocklistCache = ParseExtensionList(list);
+            }
+            return _blocklistCache;
+        }
+    }
+
+    /// <summary>
+    /// Sets the allowlist of file extensions.
+    /// </summary>
+    /// <param name="extensions">Collection of extensions in the format ".ext" (with leading dot).</param>
+    public static void SetAllowlist(IEnumerable<string> extensions)
+    {
+        var normalized = NormalizeExtensions(extensions);
+        _allowlistCache = normalized;
+        SettingHelper.Set(AllowlistKey, string.Join(";", normalized));
+    }
+
+    /// <summary>
+    /// Sets the blocklist of file extensions.
+    /// </summary>
+    /// <param name="extensions">Collection of extensions in the format ".ext" (with leading dot).</param>
+    public static void SetBlocklist(IEnumerable<string> extensions)
+    {
+        var normalized = NormalizeExtensions(extensions);
+        _blocklistCache = normalized;
+        SettingHelper.Set(BlocklistKey, string.Join(";", normalized));
+    }
+
+    /// <summary>
+    /// Checks if a file path is allowed for preview based on the current filter settings.
+    /// </summary>
+    /// <param name="path">The file path to check.</param>
+    /// <returns>True if the file is allowed for preview, false if it should be blocked.</returns>
+    public static bool IsExtensionAllowed(string path)
+    {
+        if (string.IsNullOrEmpty(path))
+            return true;
+
+        var extension = Path.GetExtension(path);
+        
+        // Files without extensions are always allowed (includes directories)
+        if (string.IsNullOrEmpty(extension))
+            return true;
+
+        extension = extension.ToLowerInvariant();
+
+        if (UseAllowlistMode)
+        {
+            // In allowlist mode: only allow if extension is in the allowlist
+            // If allowlist is empty, allow all (no filtering)
+            return Allowlist.Count == 0 || Allowlist.Contains(extension);
+        }
+        else
+        {
+            // In blocklist mode: block if extension is in the blocklist
+            return !Blocklist.Contains(extension);
+        }
+    }
+
+    /// <summary>
+    /// Clears the cached settings, forcing a reload from the config file.
+    /// </summary>
+    public static void ClearCache()
+    {
+        _allowlistCache = null;
+        _blocklistCache = null;
+        _useAllowlistModeCache = null;
+    }
+
+    private static HashSet<string> ParseExtensionList(string list)
+    {
+        if (string.IsNullOrWhiteSpace(list))
+            return new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+
+        return new HashSet<string>(
+            list.Split(ExtensionSeparators, StringSplitOptions.RemoveEmptyEntries)
+                .Select(NormalizeExtension)
+                .Where(e => !string.IsNullOrEmpty(e)),
+            StringComparer.OrdinalIgnoreCase);
+    }
+
+    private static HashSet<string> NormalizeExtensions(IEnumerable<string> extensions)
+    {
+        return new HashSet<string>(
+            extensions.Select(NormalizeExtension).Where(e => !string.IsNullOrEmpty(e)),
+            StringComparer.OrdinalIgnoreCase);
+    }
+
+    private static string NormalizeExtension(string ext)
+    {
+        if (string.IsNullOrWhiteSpace(ext))
+            return null;
+
+        ext = ext.Trim().ToLowerInvariant();
+        if (!ext.StartsWith("."))
+            ext = "." + ext;
+
+        return ext;
+    }
+}
+
diff --git a/QuickLook/ViewWindowManager.cs b/QuickLook/ViewWindowManager.cs
index ee1ce2bdd..563ead67b 100644
--- a/QuickLook/ViewWindowManager.cs
+++ b/QuickLook/ViewWindowManager.cs
@@ -151,10 +151,15 @@ public void InvokePreview(string path = null)
         if (_viewerWindow.IsVisible && path == _invokedPath)
             return;
 
-        if (!Directory.Exists(path) && !File.Exists(path))
+        var isDirectory = Directory.Exists(path);
+        if (!isDirectory && !File.Exists(path))
             if (!path.StartsWith("::")) // CLSID
                 return;
 
+        // Check extension filtering before proceeding (skip for directories)
+        if (!isDirectory && !ExtensionFilterHelper.IsExtensionAllowed(path))
+            return;
+
         _invokedPath = path;
 
         RunFocusMonitor();
@@ -172,7 +177,12 @@ public void InvokePluginPreview(string plugin, string path = null)
         if (string.IsNullOrEmpty(path))
             return;
 
-        if (!Directory.Exists(path) && !File.Exists(path))
+        var isDirectory = Directory.Exists(path);
+        if (!isDirectory && !File.Exists(path))
+            return;
+
+        // Check extension filtering before proceeding (skip for directories)
+        if (!isDirectory && !ExtensionFilterHelper.IsExtensionAllowed(path))
             return;
 
         RunFocusMonitor();