libX11 -- Sub-object overflows

The X.Org project reports:

Buffer overflows in InitExt.c in libX11 prior to 1.8.6 [CVE-2023-3138]

    The functions in src/InitExt.c in libX11 prior to 1.8.6 do not check
    that the values provided for the Request, Event, or Error IDs are
    within the bounds of the arrays that those functions write to, using
    those IDs as array indexes.  Instead they trusted that they were called
    with values provided by an Xserver that was adhering to the bounds
    specified in the X11 protocol, as all X servers provided by X.Org do.

As the protocol only specifies a single byte for these values, an
out-of-bounds value provided by a malicious server (or a malicious
proxy-in-the-middle) can only overwrite other portions of the Display
structure and not write outside the bounds of the Display structure
itself. Testing has found it is possible to at least cause the client
to crash with this memory corruption.