The following message is a courtesy copy of an article that has been posted to comp.os.linux.misc,comp.os.linux.development.system,comp.lang.perl.misc as well. The suid script emulation in Perl 5.0004_4 (as found in SuSE Linux 5.3 and doubtless other Linux distributions) fails to take account of the nosuid mount option on filesystems. This means that it is trivial for a resourceful user to hide a setuid perl script on a CD or floppy and then use it to become root. Many systems are (even by default) configured to allow users mount floppys and CDs nosuid. The most obvious fix to Perl for this would be (where available) to use fstatvfs() (as defined in SUSv2) to determine if the script is on a filesystem that is mounted with the nosuid option. Unfortunately fstatvfs() is not implemented in Linux (as of 2.2pre1). It would not be difficult to add the new system call. Indeed the existing fstatfs() implementation could simply be modified to implement fstatvfs() semantics and both syscalls could then point to the same code. This vulerability will exist in all Unicies that use a user-space implementation of suid-scripts and impelment a nosuid mount option in such a way that it does not modify the values returned by fstat(). It is worth noting that that other suid-aware script-interpreters will probalby also display this vulnerability on Linux because of the absense of fstatvfs(). -- \\ ( ) No male bovine | Email: B.A.McCauleyat_private . _\\__[oo faeces from | Phones: +44 121 471 3789 (home) .__/ \\ /\@ /~) /~[ /\/[ | +44 121 627 2173 (voice) 2175 (fax) . l___\\ /~~) /~~[ / [ | PGP-fp: D7 03 2A 4B D8 3A 05 37... # ll l\\ ~~~~ ~ ~ ~ ~ | http://www.wcl.bham.ac.uk/~bam/ ###LL LL\\ (Brian McCauley) |
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