Libarchive through 3.6.2 can cause directories to have world-writable permissions. The umask() call inside archive_write_disk_posix.c changes the umask of the whole process for a very short period of time; a race condition with another thread can lead to a permanent umask 0 setting. Such a race condition could lead to implicit directory creation with permissions 0777 (without the sticky bit), which means that any low-privileged local user can delete and rename files inside those directories.
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