Iframe Sandboxing
The sandbox="" attribute should always be added to iframes with untrusted or third-party sources. The attribute enables different types of iframe content restrictions like script or form execution.
Crossorigin
The crossorigin="anonymous" attribute should always be added to external ressources so no user credentials are transmitted. By loading external files with a GET request, http user credentials are exchanged by default. If the source host is corrupted, an attacker could these details for attacks.
Integrity
The integrity="sha256-..." attribute should always be added to external file hosted on another domain, because an unexpected manipulation / corruption of the code can lead to session hijacking or similar script releated attacks.
Link Opener
The rel="noopener" attribute should always be added to external links, which open in a new tab, to reduce the risk of reverse tabnabbing. Otherwise javascript on the new page has full control over the previous visited page, including permission to change the DOM object and possibly steal session cookies.
Link Referrer
The rel="noreferrer" attribute should always be added to external links to prevent reverse tabnabbing for older browser, which do not support the rel="noopener" attribute and to prevent phishing attacks.
Unsafe Resource
If a resource is loaded over src="http://...", it may not be transmitted over the TLS protocol. In case the webpage is loaded over HTTPS, this results in a mixed content situation where the page is securely loaded but has unencrypted resources embedded. This will often lead to a mixed-content browser warning, but at the time this is reported, it is most likely to late and the attack could have already succeeded.
Password Pattern
The pattern="..." attribute should always be added to password fields, since a client-side password strength can not be enforced by JavaScript, if the user has disabled scripts in his browser. Make sure to perform a second check at sever-side.
Unsafe Meta
The <meta name="generator" content="WordPress x.x"></meta> and the <meta content="deny" http-equiv="X-Frame-Options"></meta> meta-tags should always be removed from the html body since the generator tag provides critical informations about the used CMS and the X-Frame-Options must be specified as HTTP Headers and not as a meta tag. Most browser will ignore the meta tag, which can lead to unintended misbehaviour.
Csrf Tokens
Cross-site request forgery, also known as one-click attack or session riding, is a type of malicious exploit of a website where unauthorized commands are transmitted from a authenticated user on the web application. One way of performing such an attack is to observe the HTML code of a website for session tokens like in <input> tags, which should never be stored inside of the HTML-document.
Enabled Debugging
If the debugging is enabled on a production server, it may give an agressor valuable informations about the inner structure of a web application. These can be used to find vulnerabilities for injections or other type of attacks. Therefore, debugging should always be disabled.
