mod/forum/externallib.php in Moodle 2.6.x before 2.6.6 and 2.7.x before 2.7.3 does not verify group permissions, which allows remote authenticated users to access a forum via the forum_get_discussions web service.
git.moodle.org/gw?p=moodle.git&a=search&h=HEAD&st=commit&s=MDL-45303
openwall.com/lists/oss-security/2014/11/17/11
github.com/moodle/moodle
github.com/moodle/moodle/commit/3aa9d93c7a78d14fa30e2afbfd8fa7e09bc9cb41
github.com/moodle/moodle/commit/40afeb4044c9718bf175c347f0f9099a037ce9f0
github.com/moodle/moodle/commit/79eda0e9a0d15ba1d87187ec712f96abd62748c1
moodle.org/mod/forum/discuss.php?d=275159
nvd.nist.gov/vuln/detail/CVE-2014-7834
web.archive.org/web/20150914064838/www.securitytracker.com/id/1031215