Files
PowerToys/src/common/FilePreviewCommon/MarkdownHelper.cs
leileizhang 876130c3cd Fix Peek allowing Local File Inclusion (LFI) and RCE (#44601)
<!-- Enter a brief description/summary of your PR here. What does it
fix/what does it change/how was it tested (even manually, if necessary)?
-->
## Summary of the Pull Request
In PR #44456, we disabled scripts and HTML, but we still want to allow
HTML rendering.

This pull request introduces significant security improvements and UI
enhancements to the file previewer, focusing on safe rendering of files
and better user communication when opening external links. The main
changes include strict resource filtering to prevent external content
loading (and potential XSS attacks), a more informative dialog when
opening external URIs, and improved logic for determining how different
file types are previewed.

**Security enhancements:**

* Added strict resource filtering for non-dev file previews in
`BrowserControl` to block external HTTP/S requests and limit local file
access to the same directory and subdirectories, preventing XSS and
unwanted external content loading.
* Set the `WEBVIEW2_ADDITIONAL_BROWSER_ARGUMENTS` environment variable
to block new web contents for extra security.
* Removed disabling of HTML rendering in the Markdown pipeline to allow
safe local rendering (now protected by resource filtering).

**File preview logic improvements:**

* Refactored previewer logic to prioritize file type handling: Markdown,
SVG, HTML/HTM, Monaco-supported source code, and fallback types,
ensuring correct preview strategy and context menu behavior for each
type.
* Resource filtering is dynamically applied or removed based on whether
the file is a dev/source code file (Monaco editor) or not, ensuring
compatibility and security.

**User interface enhancements:**

* Updated the open URI dialog to include a warning banner and improved
messaging, informing users about the risks of opening external links.

<img width="1174" height="336" alt="image"
src="https://github.com/user-attachments/assets/db6b2a11-c972-473a-a1bc-a24f3244f18f"
/>

<!-- Please review the items on the PR checklist before submitting-->
## PR Checklist

- [x] Closes: #44600
<!-- - [ ] Closes: #yyy (add separate lines for additional resolved
issues) -->
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

<!-- Provide a more detailed description of the PR, other things fixed,
or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

use this file for testing

[test-xss-vulnerability.md](https://github.com/user-attachments/files/24486900/test-xss-vulnerability.md)
<img width="1547" height="1257" alt="image"
src="https://github.com/user-attachments/assets/2047007c-1ee1-487c-96aa-30e82ac63f18"
/>
2026-01-08 14:57:10 +08:00

54 lines
6.7 KiB
C#

// Copyright (c) Microsoft Corporation
// The Microsoft Corporation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System.IO;
using Markdig;
namespace Microsoft.PowerToys.FilePreviewCommon
{
public static class MarkdownHelper
{
/// <summary>
/// Markdown HTML header for light theme.
/// </summary>
private static readonly string HtmlLightHeader = "<!doctype html><style>body{width:100%;margin:0;font-family:-apple-system,BlinkMacSystemFont,\"Segoe UI\",Roboto,\"Helvetica Neue\",Arial,\"Noto Sans\",sans-serif,\"Apple Color Emoji\",\"Segoe UI Emoji\",\"Segoe UI Symbol\",\"Noto Color Emoji\";font-size:1rem;font-weight:400;line-height:1.5;color:#212529;text-align:left;background-color:#fff}.container{padding:5%}body img{max-width:100%;height:auto}body h1,body h2,body h3,body h4,body h5,body h6{margin-top:24px;margin-bottom:16px;font-weight:600;line-height:1.25}body h1,body h2{padding-bottom:.3em;border-bottom:1px solid #eaecef}body{font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Helvetica,Arial,sans-serif,Apple Color Emoji,Segoe UI Emoji}body h3{font-size:1.25em}body h4{font-size:1em}body h5{font-size:.875em}body h6{font-size:.85em;color:#6a737d}pre{font-family:SFMono-Regular,Consolas,Liberation Mono,Menlo,monospace;background-color:#f6f8fa;border-radius:3px;padding:16px;font-size:85%}a{color:#0366d6}strong{font-weight:600}em{font-style:italic}code{padding:.2em .4em;margin:0;font-size:85%;background-color:#f6f8fa;border-radius:3px}hr{border-color:#EEE -moz-use-text-color #FFF;border-style:solid none;border-width:.5px 0;margin:18px 0}table{display:block;width:100%;overflow:auto;border-spacing:0;border-collapse:collapse}tbody{display:table-row-group;vertical-align:middle;border-color:inherit;vertical-align:inherit;border-color:inherit}table tr{background-color:#fff;border-top:1px solid #c6cbd1}tr{display:table-row;vertical-align:inherit;border-color:inherit}table td,table th{padding:6px 13px;border:1px solid #dfe2e5}th{font-weight:600;display:table-cell;vertical-align:inherit;font-weight:bold;text-align:-internal-center}thead{display:table-header-group;vertical-align:middle;border-color:inherit}td{display:table-cell;vertical-align:inherit}code,pre,tt{font-family:SFMono-Regular,Menlo,Monaco,Consolas,\"Liberation Mono\",\"Courier New\",monospace;color:#24292e;overflow-x:auto}pre code{display:block;font-size:inherit;color:inherit;word-break:normal}blockquote{background-color:#fff;border-radius:3px;padding:15px;font-size:14px;display:block;margin-block-start:1em;margin-block-end:1em;margin-inline-start:40px;margin-inline-end:40px;padding:0 1em;color:#6a737d;border-left:.25em solid #dfe2e5}</style><body><div class=\"container\">";
/// <summary>
/// Markdown HTML header for dark theme.
/// </summary>
private static readonly string HtmlDarkHeader = "<!doctype html><style>body{width:100%;margin:0;font-family:-apple-system,BlinkMacSystemFont,\"Segoe UI\",Roboto,\"Helvetica Neue\",Arial,\"Noto Sans\",sans-serif,\"Apple Color Emoji\",\"Segoe UI Emoji\",\"Segoe UI Symbol\",\"Noto Color Emoji\";font-size:1rem;font-weight:400;line-height:1.5;color:#d4d4d4;text-align:left;background-color:#1e1e1e}.container{padding:5%}body img{max-width:100%;height:auto}body h1,body h2,body h3,body h4,body h5,body h6{margin-top:24px;margin-bottom:16px;font-weight:600;line-height:1.25}body h1,body h2{padding-bottom:.3em;border-bottom:1px solid #474747}body{font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Helvetica,Arial,sans-serif,Apple Color Emoji,Segoe UI Emoji}body h3{font-size:1.25em}body h4{font-size:1em}body h5{font-size:.875em}body h6{font-size:.85em;color:#d4d4d4}pre{font-family:SFMono-Regular,Consolas,Liberation Mono,Menlo,monospace;background-color:#161616;border-radius:3px;padding:16px;font-size:85%}a{color:#0366d6}strong{font-weight:600}em{font-style:italic}code{padding:.2em .4em;margin:0;font-size:85%;background-color:#161616;border-radius:3px}hr{border-color:#EEE -moz-use-text-color #FFF;border-style:solid none;border-width:.5px 0;margin:18px 0}table{display:block;width:100%;overflow:auto;border-spacing:0;border-collapse:collapse}tbody{display:table-row-group;vertical-align:middle;border-color:inherit;vertical-align:inherit;border-color:inherit}table tr{background-color:#1e1e1e;border-top:1px solid #c6cbd1}tr{display:table-row;vertical-align:inherit;border-color:inherit}table td,table th{padding:6px 13px;border:1px solid #474747}th{font-weight:600;display:table-cell;vertical-align:inherit;font-weight:bold;text-align:-internal-center}thead{display:table-header-group;vertical-align:middle;border-color:inherit}td{display:table-cell;vertical-align:inherit}code,pre,tt{font-family:SFMono-Regular,Menlo,Monaco,Consolas,\"Liberation Mono\",\"Courier New\",monospace;color:#d4d4d4;overflow-x:auto}pre code{display:block;font-size:inherit;color:inherit;word-break:normal}blockquote{background-color:#282828;border-radius:3px;padding:15px;font-size:14px;display:block;margin-block-start:1em;margin-block-end:1em;margin-inline-start:40px;margin-inline-end:40px;padding:0 1em;color:#d4d4d4;border-left:.25em solid #d4d4d4}</style><body><div class=\"container\">";
/// <summary>
/// Markdown HTML footer.
/// </summary>
private static readonly string HtmlFooter = "</div></body></html>";
public static string MarkdownHtml(string fileContent, string theme, string filePath, ImagesBlockedCallBack imagesBlockedCallBack)
{
var htmlHeader = theme == "dark" ? HtmlDarkHeader : HtmlLightHeader;
// Extension to modify markdown AST.
HTMLParsingExtension extension = new HTMLParsingExtension(imagesBlockedCallBack);
extension.FilePath = Path.GetDirectoryName(filePath) ?? string.Empty;
// if you have a string with double space, some people view it as a new line.
// while this is against spec, even GH supports this. Technically looks like GH just trims whitespace
// https://github.com/microsoft/PowerToys/issues/10354
var softlineBreak = new Markdig.Extensions.Hardlines.SoftlineBreakAsHardlineExtension();
MarkdownPipelineBuilder pipelineBuilder;
pipelineBuilder = new MarkdownPipelineBuilder().UseAdvancedExtensions().UseEmojiAndSmiley().UseYamlFrontMatter().UseMathematics();
pipelineBuilder.Extensions.Add(extension);
pipelineBuilder.Extensions.Add(softlineBreak);
MarkdownPipeline pipeline = pipelineBuilder.Build();
string parsedMarkdown = Markdown.ToHtml(fileContent, pipeline);
string markdownHTML = $"{htmlHeader}{parsedMarkdown}{HtmlFooter}";
return markdownHTML;
}
}
}