Users with the "login as other users" capability (such as administrators/managers) can access other users' Dashboards, but the JavaScript those other users may have added to their Dashboard was not being escaped when being viewed by the user logging in on their behalf.
Please note that for versions 3.1 and 3.4 only, this fix removes access to other users' Dashboards while using the login-as functionality. Versions 3.5 and 3.6 have additional sanitizing implemented, which allowed the risk to be removed while retaining Dashboard access. If you require access to Dashboards through the login-as feature, we recommend upgrading to Moodle 3.5 or above (noting that 3.1 and 3.4 will also no longer receive security updates after their next releases in May 2019).
| Severity/Risk: | Serious |
| Versions affected: | 3.6 to 3.6.2, 3.5 to 3.5.4, 3.4 to 3.4.7, 3.1 to 3.1.16 and earlier unsupported versions |
| Versions fixed: | 3.6.3, 3.5.5, 3.4.8 and 3.1.17 |
| Reported by: | Daniel Thatcher |
| Workaround: | Use incognito/private browsing mode when using the "Log in as" functionality, then close the private window before logging back in as your own user, to minimise session or cookie related risks. Alternatively, avoid visiting the Dashboard when logged in as other users until patch is applied. |
| CVE identifier: | CVE-2019-3847 |
| Changes (master): | http://git.moodle.org/gw?p=moodle.git&a=search&h=HEAD&st=commit&s=MDL-63786 |
| Tracker issue: | MDL-63786 "Log in as" functionality exposed to JavaScript risk on other users' Dashboards |