MEDIUM
The open_log function in log.c in Exim 4.72 and earlier does not check the return value from (1) setuid or (2) setgid system calls, which allows local users to append log data to arbitrary files via a symlink attack.
ftp://ftp.exim.org/pub/exim/ChangeLogs/ChangeLog-4.74
http://lists.exim.org/lurker/message/20110126.034702.4d69c278.en.html
http://lists.opensuse.org/opensuse-security-announce/2011-02/msg00004.html
http://secunia.com/advisories/43101
http://secunia.com/advisories/43128
http://secunia.com/advisories/43243
http://www.debian.org/security/2011/dsa-2154
http://www.securityfocus.com/bid/46065
http://www.ubuntu.com/usn/USN-1060-1
http://www.vupen.com/english/advisories/2011/0224
http://www.vupen.com/english/advisories/2011/0245
http://www.vupen.com/english/advisories/2011/0364