The Btrfs implementation in the Linux kernel before 3.19 does not ensure that the visible xattr state is consistent with a requested replacement, which allows local users to bypass intended ACL settings and gain privileges via standard filesystem operations (1) during an xattr-replacement time window, related to a race condition, or (2) after an xattr-replacement attempt that fails because the data does not fit.
3.13.0-57.953.16.0-38.52~14.04.14.15.0-1002.24.15.0-1003.34.15.0-1004.44.15.0-1008.84.15.0-1009.94.15.0-1012.124.15.0-1013.134.15.0-1014.144.15.0-1018.184.15.0-1019.19+34 more4.15.0-1001.14.15.0-1003.34.15.0-1005.54.15.0-1006.64.15.0-1008.84.15.0-1009.94.15.0-1010.104.15.0-1014.144.15.0-1015.154.15.0-1017.18+28 more4.18.0-13.14~18.04.14.18.0-14.15~18.04.14.18.0-15.16~18.04.14.18.0-16.17~18.04.14.18.0-17.18~18.04.14.18.0-18.19~18.04.14.18.0-20.21~18.04.14.18.0-21.22~18.04.14.18.0-22.23~18.04.14.18.0-24.25~18.04.1+33 more5.0.0-15.16~18.04.15.0.0-16.17~18.04.15.0.0-17.18~18.04.15.0.0-19.20~18.04.15.0.0-20.21~18.04.15.3.0-19.20~18.04.25.3.0-22.24~18.04.15.3.0-23.25~18.04.15.3.0-23.25~18.04.25.3.0-24.26~18.04.25.4.0-1063.66+cvm2.25.4.0-1063.66+cvm3.25.4.0-1064.67+cvm1.15.4.0-1065.68+cvm2.15.4.0-1067.70+cvm1.15.4.0-1068.71+cvm1.15.4.0-1069.72+cvm1.15.4.0-1070.73+cvm1.15.4.0-1072.75+cvm1.15.4.0-1073.76+cvm1.1+16 more5.4.0-1033.355.4.0-1035.375.4.0-1036.385.4.0-1037.395.4.0-1039.415.4.0-1041.435.4.0-1042.445.4.0-1043.455.4.0-1044.465.4.0-1046.48+41 more5.4.0-1008.95.4.0-1009.105.4.0-1010.115.4.0-1011.125.4.0-1012.135.4.0-1013.145.4.0-1014.155.4.0-1015.165.4.0-1016.175.4.0-1018.19+68 more5.3.0-1007.85.3.0-1014.165.3.0-1015.175.3.0-1017.195.4.0-1004.45.4.0-1006.6