CiviCRM versions 5.3.0 and 4.6.37 (and earlier)
CiviCRM version 5.3.1 and 4.6.38 (and later)
The "context" parameter for a number of screens was not properly validated. In some screens, this was found to enable cross-site scripting attacks. To correct the known vulnerability and to guard against potential others, the validation rules have been tightened across a wide range of screens.
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