DOMPurify VS remark

DOMPurify

I saw that some people were injecting alerts. If you haven't fixed it yet, consider using something like DOMPurify to sanitize the HTML input before posting it to the db.

You mean from this article "Sanitize HTML strings"? https://phuoc.ng/collection/html-dom/sanitize-html-strings/

Yeah, that article really shouldn't imply that sanitization is "that easy". It does at least mention https://github.com/cure53/DOMPurify at the end but it should LOUDLY argue against attempting to write this particular thing yourself and promote that exclusively in my opinion.

It is highly recommended to use an XSS Sanitizer like DOMPurify to sanitize HTML and prevent XSS attacks. For Next.js projects, which prominently feature server-side rendering, Isomorphic DOMPurify is especially valuable. It offers a seamless sanitization process across both server and client, ensuring consistent HTML sanitization in environments like Next.js where a native server-side DOM isn't present.

Note: We’ve used DOMPurify to sanitize the HTML in the above code block. You can install it in Node.js with npm install dompurify. Include it in your HTML with .

body, input.value property, or body are all different). If you need to insert untrusted input into raw HTML, use a well-tested sanitizer such as DOMPurify.

Setting a strong Content Security Policy without unsafe-inline or unsafe-eval in the script-src or default-src directives is an effective defense-in-depth) measure to prevent modern browsers from executing attacker code even if the attacker is able to insert </code> elements into the page.</p> <p><strong>3. HTTP API injection</strong></p> <p>RESTful APIs, GraphQL, and other HTTP-based APIs are ubiquitous. When a web application makes an API call to another service, injection vulnerabilities are possible when that request includes untrusted input.</p> <p>Consider a contrived example in which a web app integrates with a payments service that has a REST API endpoint for creating a subscription: <code>POST /subscriptions/{product_id}?price_usd=<price></code> where <code>price_usd</code> is optional, and a pre-configured price is used if omitted. If an attacker controls the value of <code>product_id</code> and passes a value of <code>desired_product_id?price_id=0</code>, the web app would end up making a request to <code>POST /subscriptions/desired_product_id?price_id=0</code>, which would allow the attacker to sign up for a free subscription.</p> <p>In JavaScript, the standard way to sanitize untrusted inputs in URL paths is <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURIComponent"><code>encodeURIComponent</code></a>, which replaces problematic characters such as <code>?</code> and <code>/</code> with safe percent-encoded sequences. When inserting untrusted input into URL query parameters, <a href="https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams/URLSearchParams"><code>new URLSearchParams(queryParams)</code></a> provides a convenient, safe interface for building a query string from a JavaScript object of key-value pairs.</p> <p><strong>4. Shell injection</strong></p> <p>Backend APIs sometimes need to execute external commands on the machine where they run. Consider an API that performs <a href="https://en.wikipedia.org/wiki/WHOIS">WHOIS</a> lookups for a requested domain by executing the <code>whois</code> command locally.</p> <p>Consider the following <strong>vulnerable</strong> Node.js code:</p> <pre><code>const whois = child_process.execSync(`whois ${whoisRequest.domain}`); </code></pre> <p>If an attacker can pass the domain <code>reddit.com && rm -rf /</code>, the backend will execute the command <code>whois reddit.com && rm -rf /</code>. The <a href="https://nodejs.org/api/child_process.html#child_processexecsynccommand-options"><code>child_process.execSync</code></a> function passes the command string to the shell (<code>/bin/sh</code> by default on Linux), which parses <code>&& rm -rf /</code> as a subsequent command to wipe the filesystem.</p> <p>To avoid this issue, <strong>never pass untrusted input to a shell</strong>. Instead, use an interface such as <a href="https://nodejs.org/api/child_process.html#child_processexecfilesyncfile-args-options"><code>child_process.execFileSync</code></a> that executes a specific binary (which shouldn't be a shell!) and passes arguments <em>as an array</em>:</p> <pre><code>const whois = child_process.execFileSync("whois", [whoisRequest.domain]); </code></pre> <p>Now, even if the user passes a domain <code>reddit.com && rm -rf /</code>, that entire string will be passed as the command-line argument to <code>whois</code>, which will exit with an error but will not cause any harmful side-effects. Perhaps an even better solution would be to use a library to perform WHOIS queries without needing to execute a separate command.</p> <p>Astute readers may point out that validating the domain against a regex would also likely prevent shell injection in this case. However, avoiding the possibility of shell injection by using a safe interface that keeps untrusted input away from a shell's command parser is a more robust solution that avoids shell injection in all cases.</p> <p><strong>5. Path traversal</strong></p> <p>Finally, a path traversal vulnerability arises when an untrusted input is inserted into a filesystem path, which can cause the wrong file to be read or even written. Consider a backend API that reads a file at the path <code>/teams/${team_id}/${report_name}.csv</code>. If an attacker controls the value of <code>report_name</code> but not <code>team_id</code>, they could pass a <code>report_name</code> of <code>../other_team_id/private.</code> This would cause the file <code>/teams/team_id/../other_team_id/private.csv</code> (resolved to <code>/teams/other_team_id/private.csv</code>) to be read, leaking data from a different team.</p> <p>To avoid path traversal vulnerabilities, <strong>never use untrusted input in file or directory names</strong>. It's safest always to control the names of files and directories, including IDs that you generate and control (e.g., UUIDs, KSUIDs, etc.). If the name of a file or directory absolutely <em>must</em> be derived from untrusted input, consider hashing it (e.g., using SHA-256) or at least encoding it into a format that doesn't include dots or slashes (e.g., <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-5">URL-safe base64</a>).</p> <p>​</p> <p>Know of good Node.js libraries for avoiding injection vulnerabilities? Let folks know in the comments!</p> </div><!-- SC_ON -->

https://stackoverflow.com/questions/43584685/input-sanitization-in-reactjs https://www.npmjs.com/package/dompurify

If you're using an external view engine, or a javascript framework like react in addition to your ruby backend, you can rely on similar sanitization methods like the DOMPurify library.

You shouldn't roll your own for this. From what I've had to do web-wise, here's a few tools.

First, for the APIs, you need documentation: https://swagger.io/

From which you can generate JSON schemas and use those to validate in the browser and on the backend. https://www.npmjs.com/package/jsonschema

As well you should be writing a few more schemas for your application state and leverage the regex validation of your input components...

Speaking of which, you also need to sanitize out some potentially nasty input. https://www.npmjs.com/package/dompurify

Obviously this isn't everything and not perfect, but a lot of this tedium can be automated away if you have a few good examples of the happy path and some basic tests in place to prevent quick and dirty changes from poking holes in these layers.

I also didn't try this tool but it's called RemarkJS which is named too similar to revealjs.

remark. Primarily, this is a linter for Markdown. Additionally, thanks to its numerous plugins, it allows us to perform additional checks for grammatical mistakes within the content itself. Before using this linter, our content was not scrutinized to this extent.

Rehype and Remark are plugins used to transform and manipulate the HTML and Markdown content of a website, helping to enhance its functionality and appearance.

I usually combine remark-parse, remark-rehype and rehype-react to transform markdown into react components. The configuration of the processor is like:

Astro content collection are as simple as a folder containing a bunch of Markdown (or Markdoc or MDX) files if that's the only thing you need, but they can also do relationship matching between different collections, frontmatter validation using zod and you can also customize how the markdown is parsed and translated to html using rehype and remark and their plugin ecosystem.

On my personal blog I have few external links in my posts. I wanted to keep people on my website by applying target="_blank" on external (those what don't reference to my site) links. This is a common and good practice too. I write my content in Markdown, so I decided to write a remark plugin. It is simple to implement, just few lines of code.

Although we are building a custom table of contents, we won't have to write everything from scratch. To separate the Markdown/MDX content from the front matter, we'll use the Gray-matter package. It is optional in case you don't have front matter in your Markdown files. To process the Markdown itself, we'll use the Remark package. We'll also need the unist-util-visit package for traversing node trees and mdast-util-to-string for getting the text content of a node.

That's all to render the post as HTML, there are lots of things you can do to customize the results, you can check the remark plugins and rehype plugins to pass as props to and you can also take a look at some other bloggers if you're looking for different styles for example Lee Robinson's or if you liked mine.

contentlayer uses remark to parse the markdown in an mdast. We can now use remark plugins to modify the mdast. Then rehype comes into play and converts the mdast into a hast. rehype plugins can now modify the hast. Finally the hast is converted into react components.

Now we have our Cloudinary account set up, we can use it with Docusaurus. To do so, we need to create a remark plugin. This is a plugin for the remark markdown processor. It's a plugin that will transform the markdown image syntax into a Cloudinary URL.