mod/assign/externallib.php in Moodle 2.6.x before 2.6.2 does not properly handle assignment web-service parameters, which might allow remote authenticated users to modify grade metadata via unspecified vectors.
https://moodle.org/mod/forum/discuss.php?d=256425
http://openwall.com/lists/oss-security/2014/03/17/1
http://git.moodle.org/gw?p=moodle.git&a=search&h=HEAD&st=commit&s=MDL-43468