lbxproxy converts it's display agrument to an int without checking
for an integer overflow. It then uses this value in trying to establish
connections, increasing the number after each attempt (again, without
checking for an overflow):

jjj@enigma 486> lbxproxy :2147483648
Failed to establish all listening sockets for port number '2147483648'
Failed to establish all listening sockets for port number '-2147483647'
Failed to establish all listening sockets for port number '-2147483646'
Failed to establish all listening sockets for port number '-2147483645'
Failed to establish all listening sockets for port number '-2147483644'
Failed to establish all listening sockets for port number '-2147483643'
^C
Killed

This results in a large number of sockets in /tmp/.X11-unix:
[...]
X-2147483545  X-2147483569  X-2147483593  X-2147483617  X-2147483641
X-2147483546  X-2147483570  X-2147483594  X-2147483618  X-2147483642
X-2147483547  X-2147483571  X-2147483595  X-2147483619  X-2147483643
X-2147483548  X-2147483572  X-2147483596  X-2147483620  X-2147483644
X-2147483549  X-2147483573  X-2147483597  X-2147483621  X-2147483645
X-2147483550  X-2147483574  X-2147483598  X-2147483622  X-2147483646
X-2147483551  X-2147483575  X-2147483599  X-2147483623  X-2147483647
[...]

*** Test Case ***
Run 'lbxproxy :2147483648'
It should issue a single fatal error and exit without trying to open any
negative port numbers.