CVE 2015-5267
lib/moodlelib.php in Moodle through 2.6.11, 2.7.x before 2.7.10, 2.8.x before 2.8.8, and 2.9.x before 2.9.2 relies on the PHP mt_rand function to implement the random_string and complex_
See the
CVE page on Mitre.org
for more details.