Discourse Security

We take security very seriously at Discourse. We welcome any peer review of our 100% open source code to ensure nobody's Discourse forum is ever compromised or hacked.

Where should I report security issues?

In order to give the community time to respond and upgrade we strongly urge you report all security issues privately. Please use our vulnerability disclosure program at Hacker One to provide details and repro steps and we will respond ASAP. If you are unable to use Hacker One, email us directly at team@discourse.org with details and repro steps. Security issues always take precedence over bug fixes and feature work. We can and do mark releases as "urgent" if they contain serious security fixes.

Please note: Due to a significant number of low quality security reports sent via email, we are unlikely to act on security reports sent to us via email unless they come from a trusted source, and include details on the vulnerability and step by step instructions to reproduce it. Theoretical reports without a proof of concept are not accepted. We strongly recommend you follow the Hacker One submission protocols.

For a list of recent security commits, check our GitHub commits prefixed with SECURITY.

Password Storage

Discourse uses the PBKDF2 algorithm to encrypt salted passwords. This algorithm is blessed by NIST. Security experts on the web tend to agree that PBKDF2 is a secure choice.

Discourse currently uses PBKDF2 with the sha256 hashing algorithm and 600,000 iterations.

XSS

The main vector for XSS attacks is via the post composer, as we allow users to enter Markdown, HTML (a safe subset thereof), and BBCode to format posts.

There are 3 main scenarios we protect against:

Markdown preview invokes an XSS. This is possibly severe in one specific case: when a forum staff member edits a user's post, seeing the raw markup, where a malicious user may have inserted code to run JavaScript. This code would only show up in the preview, but it would run in the context of a forum staff member, which is very bad.
Markdown displayed on the page invokes an XSS. To protect against client side preview XSS, Discourse uses xss.js in the preview window.
CSP is on by default for all Discourse installations as of Discourse 2.2. It can be switched off in the site settings, but it is default on.

On the server side we run a allowlist based sanitizer, implemented using the Sanitize gem. See the relevant Discourse code.

In addition, titles and all other places where non-admins can enter code are protected either using the Handlebars library or standard Rails XSS protection.

CSRF

CSRF allows malicious sites to perform HTTP requests in the context of a forum user without their knowledge -- mostly by getting users who already hold a valid forum login cookie to click a specific link in their web browser.

Discourse extends the built-in Rails CSRF protection in the following ways:

By default any non GET requests ALWAYS require a valid CSRF token. If a CSRF token is missing Discourse will raise an exception.
API calls using the secret API bypass CSRF checks.
Certain pages are "cacheable", we do not render the CSRF token (<meta name='csrf-token' ...) on any cacheable pages. Instead when users are about to perform the first non GET request they retrieve the token just in time via GET session/csrf

DDOS

If you install via our recommended Docker image in our install guide, nginx is the front end web server. For additional DDOS protection we recommend placing HAProxy in front.

Deployment concerns

We strongly recommend that the various Discourse processes (web server, sidekiq) run under a non-elevated account. This is handled automatically if you install via our recommended Docker image -- see our install guide for details.

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