useradd in shadow-utils before 4.0.3, and possibly other versions before 4.0.8, does not provide a required argument to the open function when creating a new user mailbox, which causes the mailbox to be created with unpredictable permissions and possibly allows attackers to read or modify the mailbox.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A10807
https://issues.rpath.com/browse/RPL-1357
https://exchange.xforce.ibmcloud.com/vulnerabilities/26958
http://www.vupen.com/english/advisories/2007/3229
http://www.vupen.com/english/advisories/2006/2006
http://www.securitytracker.com/id?1018221
http://www.securityfocus.com/bid/18111
http://www.securityfocus.com/archive/1/468336/100/0/threaded
http://www.redhat.com/support/errata/RHSA-2007-0431.html
http://www.redhat.com/support/errata/RHSA-2007-0276.html
http://www.mandriva.com/security/advisories?name=MDKSA-2006:090
http://www.kb.cert.org/vuls/id/312692
http://www.gentoo.org/security/en/glsa/glsa-200606-02.xml
http://support.avaya.com/elmodocs2/security/ASA-2007-249.htm
http://secunia.com/advisories/27706
http://secunia.com/advisories/26909
http://secunia.com/advisories/25896
http://secunia.com/advisories/25894
http://secunia.com/advisories/25629
http://secunia.com/advisories/25267
http://secunia.com/advisories/25098
http://secunia.com/advisories/20506
http://secunia.com/advisories/20370
http://lists.grok.org.uk/pipermail/full-disclosure/2007-September/065902.html