Entry Restriction Results.
We rst checked our implementation of entry restriction
against the stated security goals and found that assertion 2
above was violated. We conrmed that this violation also
existed in our implementation at that time and note (with
some sheepishness) that the implementation bug resembles
ones previously found by [9] in Referer validation defenses
proposed by [32].
The violation, illustrated in Figure 2, occurs because of
HTTP redirects. Suppose origin bank:com is a victim origin
that uses entry-point restriction, and origin attack:com is
a external origin that does not use entry-point restriction.
A page created by bank:com is allowed by the browser to
cause a request for a non-entry resource in attack:com, since
attack:com does not use entry-point restriction. attack:com
may then issue a redirect to the browser telling it to nd the
requested resource back at bank:com. The browser will then
re-issue the request, now to bank:com, which will be granted
by bank:com because the request was initiated by a context
owned by bank:com. This violates the integrity goal because
the external origin attack:com plays a role in redirecting the
request back to bank:com, thus
equesting" the non-entry
resource.
To x this violation, we updated our implementation