Google's Style Guide has basic formatting and other guidance.
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- Mozilla Observatory - web security checks (also links to a couple of the below)
- SSL Labs - TLS security checker
- Hardenize - domain/email/web security checks
- SecurityHeaders - security checks on HTTP headers
- Same-Origin Policy (SOP). Security. (Related CORS - not really security, just DRM.)
- The Same Origin Policy (SOP) applies only to scripts accessing data from another origin.
- CORS can be used to relax restrictions for scripts.
- Websockets do not use SOP, the server must verify the
- SOP does not prevent "Simple Requests" (e.g. HTML forms), but does prevent reading the response. This means to prevent CSRF, the server must verify the
- Older browsers do not send the
- Content Security Policies let website owners control which resources they allow themselves [the links on the page] to load.
- HTTP Headers and HTML meta tag intersect.
- Feature Policies let website owners control which permissions they allow themselves [the scripts on the page] to use.
- Cross-Origin Resource Sharing let website owners allow which resources they allow others to load.
- With exceptions that allow hotlinking for legacy resources images, scripts, css, and audio/video.
- SOP applies to XHR, web fonts, and a couple of other things, and CORS can be used to relax these restrictions.
- CSRF - server accepting requests it believe came from the user (exploit server's trust in client)
- XSS - inject scripts into the attacked website to bypass SOP (exploit client's trust in server - for XSS originating from server)
- Reflected XSS, Persistent XSS, Self-XSS.
- This game might be helpful: https://xss-game.appspot.com/
- Storage access (cookies, sessionStorage, localStorage, IndexDB)
- Remember: many (all?) of these headers are only needed on rendered content (HTML, not images)