  We identify class of covert channels in browsers that are not mitigated by
current defenses, which we call "pool-party" attacks. Pool-party attacks allow
sites to create covert channels by manipulating limited-but-unpartitioned
resource pools. These class of attacks have been known, but in this work we
show that they are both more prevalent, more practical for exploitation, and
allow exploitation in more ways, than previously identified. These covert
channels have sufficient bandwidth to pass cookies and identifiers across site
boundaries under practical and real-world conditions. We identify pool-party
attacks in all popular browsers, and show they are practical cross-site
tracking techniques (i.e., attacks take 0.6s in Chrome and Edge, and 7s in
Firefox and Tor Browser).
  In this paper we make the following contributions: first, we describe
pool-party covert channel attacks that exploit limits in application-layer
resource pools in browsers. Second, we demonstrate that pool-party attacks are
practical, and can be used to track users in all popular browsers; we also
share open source implementations of the attack and evaluate them through a
representative web crawl. Third, we show that in Gecko based-browsers
(including the Tor Browser) pool-party attacks can also be used for
cross-profile tracking (e.g., linking user behavior across normal and private
browsing sessions). Finally, we discuss possible mitigation strategies and
defenses
