As soon as the openconnect VPN client tries to call SSL_read() on a DTLS connection, it goes into an endless loop.

GDB is useless...

(gdb) bt
#0  0xffffffffff60013b in ?? ()
#1  0x00007fff4c765610 in ?? ()
#2  0x00007fff4c7ff644 in ?? ()
Backtrace stopped: previous frame identical to this frame (corrupt stack?)

The fix is already in the 1.0.0 branch in CVS; it's the second hunk of RT#1993:
http://rt.openssl.org/Ticket/Display.html?id=1993&user=guest&pass=guest

--- ssl/d1_pkt.c 2009-07-13 13:44:04.000000000 +0200
+++ ssl/d1_pkt.c 2009-07-23 12:47:41.000000000 +0200
@@ -775,7 +775,7 @@
/* Check for timeout */
if (dtls1_is_timer_expired(s))
{
- if (dtls1_read_failed(s, -1) > 0);
+ if (dtls1_read_failed(s, -1) > 0)
goto start;
}