umount in util-linux 2.8 to 2.12q, 2.13-pre1, and 2.13-pre2, and other packages such as loop-aes-utils, allows local users with unmount permissions to gain privileges via the -r (remount) option, which causes the file system to be remounted with just the read-only flag, which effectively clears the nosuid, nodev, and other flags.
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