The ext4_fill_super function in fs/ext4/super.c in the Linux kernel 2.6.27 before 2.6.27.19 and 2.6.28 before 2.6.28.7 does not validate the superblock configuration, which allows local users to cause a denial of service (NULL pointer dereference and OOPS) by attempting to mount a crafted ext4 filesystem.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A8526
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A10683
http://www.vupen.com/english/advisories/2009/3316
http://www.vupen.com/english/advisories/2009/0509
http://www.vmware.com/security/advisories/VMSA-2009-0016.html
http://www.ubuntu.com/usn/usn-751-1
http://www.securityfocus.com/archive/1/507985/100/0/threaded
http://www.debian.org/security/2009/dsa-1749
http://secunia.com/advisories/37471
http://secunia.com/advisories/36562
http://secunia.com/advisories/34394
http://rhn.redhat.com/errata/RHSA-2009-1243.html
http://kernel.org/pub/linux/kernel/v2.6/ChangeLog-2.6.28.7