There is an improper access control issue in ArcGIS Server versions 11.3 and below on Windows and Linux which, under unique circumstances, could allow a remote, low‑privileged authenticated attacker to access secure services published to a standalone (unfederated) ArcGIS Server instance. Successful exploitation results in unauthorized access to protected services outside the attacker’s originally assigned authorization boundary, constituting a scope change. If exploited, this issue would have a high impact on confidentiality, a low impact on integrity, and no impact on the availability of the software.