Several vulnerabilities have been fixed in OpenSMTPD 5.7.2:

- an oversight in the portable version of fgetln() that allows attackers to read and write out-of-bounds memory;

- multiple denial-of-service vulnerabilities that allow local users to kill or hang OpenSMTPD;

- a stack-based buffer overflow that allows local users to crash OpenSMTPD, or execute arbitrary code as the non-chrooted _smtpd user;

- a hardlink attack (or race-conditioned symlink attack) that allows local users to unset the chflags() of arbitrary files;

- a hardlink attack that allows local users to read the first line of arbitrary files (for example, root's hash from /etc/master.passwd);

- a denial-of-service vulnerability that allows remote attackers to fill OpenSMTPD's queue or mailbox hard-disk partition;

- an out-of-bounds memory read that allows remote attackers to crash OpenSMTPD, or leak information and defeat the ASLR protection;

- a use-after-free vulnerability that allows remote attackers to crash OpenSMTPD, or execute arbitrary code as the non-chrooted _smtpd user;

Further details can be found in Qualys' audit report:

http://seclists.org/oss-sec/2015/q4/17

MITRE has assigned one CVE for the use-after-free vulnerability; additional CVEs may be assigned:

http://seclists.org/oss-sec/2015/q4/23

External References:

https://www.opensmtpd.org/announces/release-5.7.2.txt
http://seclists.org/oss-sec/2015/q4/17