NSE Connection Problems on Windows?

[Rob Nicholls <robert () robnicholls co uk>]

I've recently experienced some weird behaviour running NSE scripts 
using a version of Nmap I've built myself from SVN on Windows. It seems 
to affect scripts that access the same port (e.g. ntp, snmp), where one 
or more of them seem to execute properly and then the remaining ones 
seem to hang (presumably forever). When it happens, Nmap will just say 
something like:

NSE: Active NSE Script Threads: 3 (3 waiting)

Increasing the debugging suggests that it's getting stuck in parts of 
the script that are trying to establish a connection:

NSE: Waiting: 'snmp-interfaces' (thread: 037980D8)
        stack traceback:
                [C]: in function 'connect'
                C:\Program Files\Nmap/scripts\snmp-interfaces.nse:424: 
in function <C:\Program Files\Nmap/scripts\snmp-interfaces.nse:391>
                (...tail calls...)

I've tried leaving the scan for a long time and it doesn't appear to do 
anything. If I kill the scan it sometimes ends with one or more 
occurrences of:

Socket troubles: No error

If it's any help, I don't think I've seen this happen before September. 
I can reproduce this hang with a default UDP scan like the following:

nmap xxx.xxx.xxx.xxx -sUCV -n -Pn --reason --version-intensity 0 -p 
100-200

UDP scans against a small range of ports, such as 160-170, seem to 
complete okay, which suggests the scripts themselves aren't causing the 
hang. Is it possible that this only affects UDP connections (I don't 
think my TCP scans have been affected in this way)?

For good measure, I've just tried the same scan using an SVN build on 
Linux and it seems to work fine there. Is it possible this only affects 
Windows?!

Rob

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