A TOCTOU (time-of-check time-of-use) race condition was found in the way systemd, a system and service manager, used to update file permissions and SELinux security contexts. A local attacker could use this flaw to conduct symbolic link attacks possibly leading to their ability to modify permissions / security context of a path different than originally intended / requested.
Issue found by Florian Weimer, Red Hat Product Security Team
This issue affects the versions of the systemd package, as shipped with Fedora release of 16 and 17.
This issue was discovered by Florian Weimer of the Red Hat Product Security Team.
This was assigned CVE-2013-4392:
Do you know at which place this happened? I have a hard time pinpointing it down. ;)
This is currently blocked by the need for new system calls (or making existing system calls work with O_PATH):
We need to open files to check their hard link count and make sure that is not greater than 1, so that we do not improperly relabel a file that is visible elsewhere in the file system. Without O_PATH, the open operation can have side effects, so we would introduce another type of security bug.
Addressing this would also fix the other issue (lsetfilecon is called with absolute paths, which does not prevent symbol link resolution on non-final path components), but this issue could be fixed separate if desired.
This issue affects the version of systemd as shipped with Fedora 19 and Fedora 20 and is waiting on upstream fix as indicated by comment #11.