DOMPurify
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sanitizer-api | DOMPurify | |
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5 | 42 | |
220 | 12,802 | |
3.6% | - | |
6.5 | 8.8 | |
7 days ago | 3 days ago | |
Bikeshed | JavaScript | |
GNU General Public License v3.0 or later | GNU General Public License v3.0 or later |
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sanitizer-api
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Mastering DOM manipulation with vanilla JavaScript
That entire post is poor.
• “Using regular expressions”: it suggests that this approach is acceptable within its limits. It’s not at all. As a simple example, the expression shown is trivially bypassed by "…". This is why, unlike the post claims claims, using regular expressions for cleaning HTML is not a common approach.
• (“Eliminating the script tags”: not sure quite why you’re against it, but I also want to grumble about using `[...scriptElements].forEach((s) => s.remove())` instead of `for (const s of scriptElements) { s.remove(); }` or even `Array.prototype.forEach.call(scriptElements, (s) => s.remove())`. Creating an array from that HTMLCollection is just unnecessary and a bad habit.)
• “Removing event handlers”: `value.startsWith('javascript:') || value.startsWith('data:text/html')` is inadequate. Tricks like capitalising in order to bypass such poor checks have been common for decades.
• “Retrieving the sanitized HTML”: you are now vulnerable to mXSS attacks, which undo all your effort.
• “Elements and attributes to remove from the DOM tree”: this proposes a blacklist approach and mentions a few examples of things that should be removed. Each example misses adjacent but equally-important things that should be removed. You will not get acceptable filtering if you start from this approach.
• “Simplifying HTML sanitization with external libraries”: this is pitched merely as easier, faster and cheaper, rather than as the only way to have any confidence in the result.
• “Conclusion”: as I hope I’ve shown, “The DOMParser API is one tool you can use to get the job done right.” is not an acceptable position.
Really, the article could be significantly improved by presenting it as what a common developer might think, and then scribbling all over the problematic things with these explanations of why they’re so bad, and ending with the conclusion “so: just use the DOMPurify library; consider nothing else acceptable”. (There have at times been a couple of other libraries of acceptable quality, but as far as I’m concerned, DOMPurify has long been the one that everyone should use. I note also that this article is talking about client-side filtration. I’m not familiar with the state of the art in server-side HTML sanitisation, where you probably don’t have an actual DOM; this is also a reasonable place to wish to do filtering, but the remaining active mXSS vectors might pose a challenge. I’d want to research carefully before doing anything.)
I look forward to the Sanitizer API <https://wicg.github.io/sanitizer-api/> being completed and deployed, so that DOMPurify can become just a fallback library for older browsers.
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5 injection vulnerabilities hackers don't want developers to know about (and how to prevent them)
The upcoming Sanitizer API - kinda like a native DOMPurify that provides el.setHTML() and Document.parseHTML()
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Google, Mozilla Close to Finalizing Sanitizer API for Chrome and Firefox Browse
The benefit of doing this client-side instead of server-side is that you can stay up to date with any changes that the client may make to how it's processing HTML that may have security implications. Additionally, you get to use the exact same code that the browser is ultimately using to parse the HTML, so a browser parsing bug, spec nuance, or un-specced legacy behavior that your backend developer didn't consider don't turn into serious security flaws.
Additionally, the Sanitize API does a much better job of handling contextual parsing then many other similar backend APIs. What happens when you parse an HTML fragment assuming it will live in a `div`, and then it actually get inserted into a `table` cell? The spec goes into this is more detail here: https://wicg.github.io/sanitizer-api/#strings
The downsides, of course, are those associated with any thick-client/thin-server API design—more logic on the front-end means more logic to reimplement for different consumers.
Personally, I would probably still stick with Nokogiri for my own applications, but I can see both sides of the trade-off.
DOMPurify
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JavaScript Libraries for Implementing Trendy Technologies in Web Apps in 2024
DOMPurify
- Lessons from open-source: Use window.trustedTypes to prevent DOM XSS.
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Launched my Social Media website for lonely people living abroad, all thanks to NextJS!
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.
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Mastering DOM manipulation with vanilla JavaScript
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.
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Crafting a Dynamic Blog with Next.js 13 App Directory
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.
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Mitigating DOM clobbering attacks in JavaScript
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 .
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5 injection vulnerabilities hackers don't want developers to know about (and how to prevent them)
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
orunsafe-eval
in thescript-src
ordefault-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 -->
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Is it harder to build and maintain web applications using vanilla js or react?
https://stackoverflow.com/questions/43584685/input-sanitization-in-reactjs https://www.npmjs.com/package/dompurify
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Six security risk of user input in ruby code
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.
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Wat
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.
What are some alternatives?
uBlock-issues - This is the community-maintained issue tracker for uBlock Origin
sanitize-html - Clean up user-submitted HTML, preserving whitelisted elements and whitelisted attributes on a per-element basis. Built on htmlparser2 for speed and tolerance
html-dom - Common tasks of managing HTML DOM with vanilla JavaScript. Give me 1 ⭐if it’s useful.
js-xss - Sanitize untrusted HTML (to prevent XSS) with a configuration specified by a Whitelist
hackernews - Hacker News web site source code mirror.
HtmlSanitizer - Cleans HTML to avoid XSS attacks
React - The library for web and native user interfaces.
xss-filters
hscrpt
Next.js - The React Framework
isomorphic-dompurify - Use DOMPurify on server and client in the same way
Retire.js - scanner detecting the use of JavaScript libraries with known vulnerabilities. Can also generate an SBOM of the libraries it finds.