5.3 Origin

The origin of a resource and the effective script origin of a resource are both either opaque identifiers or tuples consisting of a scheme component, a host component, a port component, and optionally extra data.

The extra data could include the certificate of the site when using encrypted connections, to ensure that if the site's secure certificate changes, the origin is considered to change as well.

These characteristics are defined as follows:

For URLs

The origin and effective script origin of the URL are the origin defined in The Web Origin Concept. [ORIGIN]

For scripts

The origin and effective script origin of a script are determined from another resource, called the owner:

If a script is in a script element
The owner is the Document to which the script element belongs.
If a script is in an event handler content attribute
The owner is the Document to which the attribute node belongs.
If a script is a function or other code reference created by another script
The owner is the script that created it.
If a script is a javascript: URL that was returned as the location of an HTTP redirect (or equivalent in other protocols)
The owner is the URL that redirected to the javascript: URL.
If a script is a javascript: URL in an attribute
The owner is the Document of the element on which the attribute is found.
If a script is a javascript: URL in a style sheet
The owner is the URL of the style sheet.
If a script is a javascript: URL to which a browsing context is being navigated, the URL having been provided by the user (e.g. by using a bookmarklet)
The owner is the Document of the browsing context's active document.
If a script is a javascript: URL to which a browsing context is being navigated, the URL having been declared in markup
The owner is the Document of the element (e.g. an a or area element) that declared the URL.
If a script is a javascript: URL to which a browsing context is being navigated, the URL having been provided by script
The owner is the script that provided the URL.

The origin of the script is then equal to the origin of the owner, and the effective script origin of the script is equal to the effective script origin of the owner.

For Document objects
If a Document's active sandboxing flag set has its sandboxed origin browsing context flag set
The origin is a globally unique identifier assigned when the Document is created.
If a Document was generated from a javascript: URL
The origin is equal to the origin of the script of that javascript: URL.
If a Document was served over the network and has an address that uses a URL scheme with a server-based naming authority
The origin is the origin of the Document's address.
If a Document was generated from a data: URL that was returned as the location of an HTTP redirect (or equivalent in other protocols)
The origin is the origin of the URL that redirected to the data: URL.
If a Document was generated from a data: URL found in another Document or in a script
The origin is the origin of the Document or script that initiated the navigation to that URL.
If a Document has the address "about:blank"
The origin of the Document is the origin it was assigned when its browsing context was created.
If a Document is an iframe srcdoc document
The origin of the Document is the origin of the Document's browsing context's browsing context container's Document.
If a Document was obtained in some other manner (e.g. a data: URL typed in by the user, a Document created using the createDocument() API, etc)
The origin is a globally unique identifier assigned when the Document is created.

When a Document is created, its effective script origin is initialized to the origin of the Document. However, the document.domain attribute can be used to change it.

For images
If an image is the image of an img element and its image data is CORS-cross-origin
The origin is a globally unique identifier assigned when the image is created.
If an image is the image of an img element and its image data is CORS-same-origin
The origin is the origin of the img element's Document.
For audio and video elements
If the media data is CORS-cross-origin
The origin is a globally unique identifier assigned when the image is created.
If the media data is CORS-same-origin
The origin is the origin of the media element's Document.
For fonts

The origin of a downloadable Web font is equal to the origin of the absolute URL used to obtain the font (after any redirects). [CSSFONTS]

The origin of a locally installed system font is equal to the origin of the Document in which that font is being used.

Other specifications can override the above definitions by themselves specifying the origin of a particular URL, script, Document, or image.

The Unicode serialization of an origin is the string obtained by applying the following algorithm to the given origin:

  1. If the origin in question is not a scheme/host/port tuple, then return the literal string "null" and abort these steps.

  2. Otherwise, let result be the scheme part of the origin tuple.

  3. Append the string "://" to result.

  4. Apply the IDNA ToUnicode algorithm to each component of the host part of the origin tuple, and append the results — each component, in the same order, separated by "." (U+002E) characters — to result. [RFC3490]

  5. If the port part of the origin tuple gives a port that is different from the default port for the protocol given by the scheme part of the origin tuple, then append a ":" (U+003A) character and the given port, in base ten, to result.

  6. Return result.

The ASCII serialization of an origin is the string obtained by applying the following algorithm to the given origin:

  1. If the origin in question is not a scheme/host/port tuple, then return the literal string "null" and abort these steps.

  2. Otherwise, let result be the scheme part of the origin tuple.

  3. Append the string "://" to result.

  4. Apply the IDNA ToASCII algorithm the host part of the origin tuple, with both the AllowUnassigned and UseSTD3ASCIIRules flags set, and append the results result.

    If ToASCII fails to convert one of the components of the string, e.g. because it is too long or because it contains invalid characters, then return the empty string and abort these steps. [RFC3490]

  5. If the port part of the origin tuple gives a port that is different from the default port for the protocol given by the scheme part of the origin tuple, then append a ":" (U+003A) character and the given port, in base ten, to result.

  6. Return result.

Two origins are said to be the same origin if the following algorithm returns true:

  1. Let A be the first origin being compared, and B be the second origin being compared.

  2. If A and B are both opaque identifiers, and their value is equal, then return true.

  3. Otherwise, if either A or B or both are opaque identifiers, return false.

  4. If A and B have scheme components that are not identical, return false.

  5. If A and B have host components that are not identical, return false.

  6. If A and B have port components that are not identical, return false.

  7. If either A or B have additional data, but that data is not identical for both, return false.

  8. Return true.

5.3.1 Relaxing the same-origin restriction

document . domain [ = domain ]

Returns the current domain used for security checks.

Can be set to a value that removes subdomains, to change the effective script origin to allow pages on other subdomains of the same domain (if they do the same thing) to access each other.

The domain attribute on Document objects must be initialized to the document's domain, if it has one, and the empty string otherwise. If the value is an IPv6 address, then the square brackets from the host portion of the <host> component must be omitted from the attribute's value.

On getting, the attribute must return its current value, unless the Document has no browsing context, in which case it must return the empty string.

On setting, the user agent must run the following algorithm:

  1. If the Document has no browsing context, throw a SecurityError exception and abort these steps.

  2. If the new value is an IP address, let new value be the new value. Otherwise, apply the IDNA ToASCII algorithm to the new value, with both the AllowUnassigned and UseSTD3ASCIIRules flags set, and let new value be the result of the ToASCII algorithm.

    If ToASCII fails to convert one of the components of the string, e.g. because it is too long or because it contains invalid characters, then throw a SecurityError exception and abort these steps. [RFC3490]

  3. If new value is not exactly equal to the current value of the document.domain attribute, then run these substeps:

    1. If the current value is an IP address, throw a SecurityError exception and abort these steps.

    2. If new value, prefixed by a "." (U+002E), does not exactly match the end of the current value, throw a SecurityError exception and abort these steps.

    3. If new value matches a suffix in the Public Suffix List, or, if new value, prefixed by a "." (U+002E), matches the end of a suffix in the Public Suffix List, then throw a SecurityError exception and abort these steps. [PSL]

      Suffixes must be compared after applying the IDNA ToASCII algorithm to them, with both the AllowUnassigned and UseSTD3ASCIIRules flags set, in an ASCII case-insensitive manner. [RFC3490]

  4. Release the storage mutex.

  5. Set the attribute's value to new value.

  6. Set the host part of the effective script origin tuple of the Document to new value.

  7. Set the port part of the effective script origin tuple of the Document to "manual override" (a value that, for the purposes of comparing origins, is identical to "manual override" but not identical to any other value).

The domain of a Document is the host part of the document's origin, if that is a scheme/host/port tuple. If it isn't, then the document does not have a domain.

The domain attribute is used to enable pages on different hosts of a domain to access each others' DOMs.

Do not use the document.domain attribute when using shared hosting. If an untrusted third party is able to host an HTTP server at the same IP address but on a different port, then the same-origin protection that normally protects two different sites on the same host will fail, as the ports are ignored when comparing origins after the document.domain attribute has been used.

5.4 Sandboxing

A sandboxing flag set is a set of zero or more of the following flags, which are used to restrict the abilities that potentially untrusted resources have:

The sandboxed navigation browsing context flag

This flag prevents content from navigating browsing contexts other than the sandboxed browsing context itself (or browsing contexts further nested inside it), auxiliary browsing contexts (which are protected by the sandboxed auxiliary navigation browsing context flag defined next), and the top-level browsing context (which is protected by the sandboxed top-level navigation browsing context flag defined below).

If the sandboxed auxiliary navigation browsing context flag is not set, then in certain cases the restrictions nonetheless allow popups (new top-level browsing contexts) to be opened. These browsing contexts always have one permitted sandboxed navigator, set when the browsing context is created, which allows the browsing context that created them to actually navigate them. (Otherwise, the sandboxed navigation browsing context flag would prevent them from being navigated even if they were opened.)

The sandboxed auxiliary navigation browsing context flag

This flag prevents content from creating new auxiliary browsing contexts, e.g. using the target attribute, the window.open() method, or the showModalDialog() method.

The sandboxed top-level navigation browsing context flag

This flag prevents content from navigating their top-level browsing context.

When the allow-top-navigation is set, content can navigate its top-level browsing context, but other browsing contexts are still protected by the sandboxed navigation browsing context flag and possibly the sandboxed auxiliary navigation browsing context flag.

The sandboxed plugins browsing context flag

This flag prevents content from instantiating plugins, whether using the embed element, the object element, the applet element, or through navigation of a nested browsing context, unless those plugins can be secured.

The sandboxed seamless iframes flag

This flag prevents content from using the seamless attribute on descendant iframe elements.

This prevents a page inserted using the allow-same-origin keyword from using a CSS-selector-based method of probing the DOM of other pages on the same site (in particular, pages that contain user-sensitive information).

The sandboxed origin browsing context flag

This flag forces content into a unique origin, thus preventing it from accessing other content from the same origin.

This flag also prevents script from reading from or writing to the document.cookie IDL attribute, and blocks access to localStorage. [WEBSTORAGE]

The sandboxed forms browsing context flag

This flag blocks form submission.

The sandboxed scripts browsing context flag

This flag blocks script execution.

The sandboxed automatic features browsing context flag

This flag blocks features that trigger automatically, such as automatically playing a video or automatically focusing a form control.

When the user agent is to parse a sandboxing directive, given a string input and a sandboxing flag set output, it must run the following steps:

  1. Split input on spaces, to obtain tokens.

  2. Let output be empty.

  3. Add the following flags to output:

Every top-level browsing context has a popup sandboxing flag set. When a browsing context is created, its popup sandboxing flag set must be empty. It is populated by the rules for choosing a browsing context given a browsing context name.

Every nested browsing context has an iframe sandboxing flag set, which is a sandboxing flag set. Which flags in a nested browsing context's iframe sandboxing flag set are set at any particular time is determined by the iframe element's sandbox attribute.

Every Document has an active sandboxing flag set, which is a sandboxing flag set. When the Document is created, its active sandboxing flag set must be empty. It is populated by the navigation algorithm.