xhr module provides access to
XMLHttpRequest functionality, also known
XMLHttpRequest object is currently fairly limited, and does not
yet implement the
methods. It also doesn't yet implement the
XMLHttpRequest object does not currently support
mozBackgroundRequest property. All security UI, such as
username/password prompts, are automatically suppressed, so if
required authentication information isn't passed to the
method, the request will fail.
Whenever this module is unloaded, all in-progress requests are immediately aborted.
By default, the
XMLHttpRequest object grants full access to any
protocol scheme, which means that it can be used to read from (but not
write to) the host system's entire filesystem. It also has unfettered
access to any local area networks, VPNs, and the internet.
XMLHttpRequest object can be used by an add-on to "phone
home" and transmit potentially sensitive user data to third
If access to the filesystem isn't prevented, it could easily be used to access sensitive user data, though this may be inconsequential if the client can't access the network.
If access to local area networks isn't prevented, malicious code could access sensitive data.
If transmission of cookies isn't prevented, malicious code could access sensitive data.
Attenuating access based on a regular expression may be ineffective if it's easy to write a regular expression that looks safe but contains a special character or two that makes it far less secure than it seems at first glance.
We may also want to consider attenuating further based on domain name
and possibly even restricting the protocol to
https: only, to reduce
Before being exposed to unprivileged code, this object needs
to be attenuated in such a way that, at the very least, it can't
access the user's filesystem. This can probably be done most securely
by white-listing the protocols that can be used in the URL passed to
open() method, and limiting them to
possibly a special scheme that can be used to access the add-on's
packaged, read-only resources.
Finally, we need to also consider attenuating http/https requests such that they're "sandboxed" and don't communicate potentially sensitive cookie information.
XMLHttpRequest. This is a constructor, so its use should always
be preceded by the
new operator. For more information about
XMLHttpRequest objects, see the MDC page on
and the Limitations section in this page.
Returns the number of
XMLHttpRequest objects that are alive (i.e., currently
active or about to be).
The number of live