The choice module in Moodle through 2.6.11, 2.7.x before 2.7.11, 2.8.x before 2.8.9, and 2.9.x before 2.9.3 allows remote authenticated users to bypass intended access restrictions by visiting a URL to add or delete responses in the closed state.
git.moodle.org/gw?p=moodle.git&a=search&h=HEAD&st=commit&s=MDL-51569
github.com/moodle/moodle
github.com/moodle/moodle/commit/02d8c8ca394ba053905f9b87c155042aabf0ce1b
github.com/moodle/moodle/commit/09bb6f19e5814deb25ae6ceb8270063430b8941f
github.com/moodle/moodle/commit/5c16db4fc561c97b6a907398ea081cdaf6590214
github.com/moodle/moodle/commit/6283c33979001b035f9fc565b869296f66a61c4e
github.com/moodle/moodle/commit/7ca8c34045eb0d2031652b452492fe4abb2c7c8a
github.com/moodle/moodle/commit/97394274ee29f0a6eecab330b5bbb8ee335e7ece
github.com/moodle/moodle/commit/bdaa571437c6357f322871b068f02a4520b7a23d
github.com/moodle/moodle/commit/fb2491effb1a7d5d7abb0efba5b3929342990514
moodle.org/mod/forum/discuss.php?d=323237
nvd.nist.gov/vuln/detail/CVE-2015-5342