Sendmail up to recent 8.9.x versions - any user may pass -bi parameter to
/usr/sbin/sendmail. This will result in aliases database rebuild. IMHO
there's no reason to allow such things, but no matter - something rather
stupid is done during rebuild:
5366 open("/etc/aliases.db", O_RDWR|O_TRUNC) = 6
What a bad luck! There's approx 0.1 sec delay due to /etc/aliases
processing (on my system). Meantime, luser might deliver any signals
to sendmail process... SIGKILL is quite good. After that, /etc/aliases.db
will be left in unusable state (no EOF marker), causing DoS:
220 Marchew ESMTP Mail Service at nimue.ids.pl ready.
mail from: myself
451 Cannot open hash database /etc/aliases: Invalid argument
rcpt to: lcamtuf
503 Need MAIL before RCPT
Exploit is trivial.
_______________________________________________________________________
Michal Zalewski [lcamtufat_private] [link / marchew] [dione.ids.pl SYSADM]
[Marchew Industries] ! [http://lcamtuf.na.export.pl] bash$ :(){ :|:&};:
[voice phone: +48 22 813 25 86] <=-=> [cellular phone: +48 501 4000 69]
Iterowac jest rzecza ludzka, wykonywac rekursywnie - boska [P. Deutsch]
This archive was generated by hypermail 2b30 : Fri Apr 13 2001 - 15:09:31 PDT