Out-of-bounds Read vulnerability in the XKB modifier map request handling of the X.Org X server. The function CheckModifierMap() processes wire data in a loop but does not sufficiently verify that the remaining bytes are within the bounds of the client request. As a result, the total number of keys processed can exceed the actual data supplied by the client, causing reads of uninitialized memory beyond the request buffer. An attacker with access to the X11 server can trigger this without user interaction, potentially disclosing memory and/or crashing the service.