Core issue
This issue is documented in Cisco bug ID CSCsb94643.
The crash dump analysis shows:
Address function file:line
000109E8 b_free buffer.c:494
00010874 b_free buffer.c:435
005F6BB8 p2IBDRelease p2ibd.c:98
0003CFDC sbdrop sockutil.c:718
00042018 tcp_input tcp_inpu.c:1551
00037E9C ipProcLocalPkt ipprrx.c:817
00037530 ipDoLocal ipprrx.c:174
00036DF0 IpRtProcMsg ip_task.c:287
00036B9C IpRouterTask ip_task.c:179
Resolution
The only workaround is to upgrade the VPN Concentrator software code to either 4.1.7.K or 4.7.2.E.