A flaw was found in the way the Linux kernel's ext4 file system driver handled non-journal file systems with an orphan list. An attacker with physical access to the system could use this flaw to crash the system or, although unlikely, escalate their privileges on the system.
A vulnerability was found when mounting the ext2 filesystem from e2fsprogs/tests/f_orphan as ext4, leading to system crash.
Upstream Linux kernel patches fixing the issue:
c9b92530 ext4: make orphan functions be no-op in no-journal mode
0e9a9a1a ext4: avoid hang when mounting non-journal filesystems with orphan list
This problem did not affect the Linux kernel packages as shipped with Red Hat Enterprise Linux 7 and MRG-2. This issue is not planned to be corrected in future updates for Red Hat Enterprise Linux 5.
This issue is rated low as exploiting it requires physical (to plug in specially prepared usb disk) or root (to mount specially prepared filesystem) access to the system. Due to the nature of the flaw, privilege escalation cannot be fully ruled out, although we believe it is unlikely.
This issue has been addressed in the following products:
Red Hat Enterprise Linux 6
Via RHSA-2016:0855 https://rhn.redhat.com/errata/RHSA-2016-0855.html