Issue #3036494 by Berdir, alexpott, rgpublic, cilefen, kerasai, regilero: Race condition in ImageStyle::createDerivative()

Issue #2554219 by nod_, larowlan, tim.plunkett, regilero, droplet, japerry, samuel.mortenson, Pere Orga, effulgentsia, benjy, Gábor Hojtsy, greggles, Wim Leers, David_Rothstein, pwolanin, neclimdul, EclipseGc, znerol: Port Cross-site Scripting - Ajax system fixes from SA-CORE-2015-003 to Drupal 8

Issue #2304949 by mpdonadio, cilefen, znerol, klausi, gaurav.goyal, regilero: Port HTTP Host header DoS fix from SA-CORE-2014-003