CVE 2011-4308
mod/forum/user.php in Moodle 1.9.x before 1.9.14, 2.0.x before 2.0.5, and 2.1.x before 2.1.2 allows remote authenticated users to discover the names of other users via unspecified vectors.
See the 
CVE page on Mitre.org
for more details.
