changelog: add notes about 4.6.4 and 5.2.3 releases

CHANGELOG.md

@@ -73,6 +73,12 @@ These are new features that's still being worked on and are in an experimental p
 
 * **Frontend**: Convert all Frontend Karma tests to Jest tests [#12224](https://github.com/grafana/grafana/issues/12224)
 
+# 5.2.3 (2018-08-29)
+
+### Important fix for LDAP & OAuth login vulnerability
+
+See [security announcement](https://community.grafana.com/t/grafana-5-2-3-and-4-6-4-security-update/10050) for details.
+
 # 5.2.2 (2018-07-25)
 
 ### Minor
@@ -441,6 +447,12 @@ The following properties have been deprecated and will be removed in a future re
   - `uri` property in `GET /api/search` -> Use new `url` or `uid` property instead
   - `meta.slug` property in `GET /api/dashboards/uid/:uid` and `GET /api/dashboards/db/:slug` -> Use new `meta.url` or `dashboard.uid` property instead
 
+# 4.6.4 (2018-08-29)
+
+### Important fix for LDAP & OAuth login vulnerability
+
+See [security announcement](https://community.grafana.com/t/grafana-5-2-3-and-4-6-4-security-update/10050) for details.
+
 # 4.6.3 (2017-12-14)
 
 ## Fixes