Date: Fri, 21 Jun 2002 18:01:16 -0600 (MDT) From: Brett Glass <brett@lariat.org> To: security@freebsd.org Subject: Possible security liability: Filling disks with junk or spam Message-ID: <200206220001.SAA26010@lariat.org>
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Two years ago, at BSDCon, I reported on a form of abuse known as a "Rumplestiltskin attack," in which an attacker guessed names in rapid succession so as to find valid e-mail addresses to spam. Well, as it turns out, one doesn't need to do this to find addresses on FreeBSD systems that can be filled with mail. /etc/passwd contains quite a few pseudo-users which, if mailed, cause the mail to be stored on the disk as if it were addressed to a real user. No one may ever read it, but it's possible to fill the partition and thereby wreak havoc. A client recently called me in puzzlement, saying that his system was misbehaving, and it turned out that this was what had happened. The address "news@victim.com" had somehow wound up on quite a few spammers' lists. He'd never used or hosted netnews, and so had no need for the pseudo-user. But that pseudo-user was there by default, and the system dutifully created a mailbox for him/her/it when the very first spam arrived. It started growing by leaps and bounds until it was -- I kid you not! -- several hundred megabytes in size. At which point the partition ran out of room. It seems to me that pseudo-users should be non-mailable, just as a basic security policy. Ideas for the best way to implement this in the default install? --Brett Glass To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-security" in the body of the message
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