[NSE] Bug (short read) in pop3-capabilities.nse

[Daniel Miller <bonsaiviking () gmail com>]

Hey list,

I would have reported this with a patch, but I never quite got the hang 
of reading from sockets in NSE scripts :(

When scanning one of the alexa top 1m hosts via IPv6, ran across this 
exception:
> NSOCK (0.8110s) TCP connection requested to 2a01:4f8:121:1262::2:110 
> (IOD #1) EID 8
> NSOCK (0.9530s) Callback: CONNECT SUCCESS for EID 8 
> [2a01:4f8:121:1262::2:110]
> NSE: TCP XXXX:42686 > 2a01:4f8:121:1262::2:110 | CONNECT
> NSOCK (0.9530s) Read request from IOD #1 [2a01:4f8:121:1262::2:110] 
> (timeout: 10000ms) EID 18
> NSOCK (1.0920s) Callback: READ SUCCESS for EID 18 
> [2a01:4f8:121:1262::2:110] (76 bytes): +OK CommuniGate Pro POP3 Server 
> 5.2.20 ready <14999.1339429588 () aenigma gr>..
> NSE: TCP XXXX:42686 < 2a01:4f8:121:1262::2:110 | +OK CommuniGate Pro 
> POP3 Server 5.2.20 ready <14999.1339429588 () aenigma gr>
>
> NSE: TCP XXXX:42686 > 2a01:4f8:121:1262::2:110 | 00000000: 43 41 50 41 
> 0d 0a                               CAPA
>
> NSOCK (1.0930s) Write request for 6 bytes to IOD #1 EID 27 
> [2a01:4f8:121:1262::2:110]: CAPA..
> NSOCK (1.0930s) Callback: WRITE SUCCESS for EID 27 
> [2a01:4f8:121:1262::2:110]
> NSE: TCP XXXX:42686 > 2a01:4f8:121:1262::2:110 | SEND
> NSOCK (1.0940s) Read request from IOD #1 [2a01:4f8:121:1262::2:110] 
> (timeout: 10000ms) EID 34
> NSOCK (1.2320s) Callback: READ SUCCESS for EID 34 
> [2a01:4f8:121:1262::2:110] (29 bytes): +OK capability list follows..
> NSE: TCP XXXX:42686 < 2a01:4f8:121:1262::2:110 | 00000000: 2b 4f 4b 20 
> 63 61 70 61 62 69 6c 69 74 79 20 6c +OK capability l
> 00000010: 69 73 74 20 66 6f 6c 6c 6f 77 73 0d 0a          ist follows
>
> NSE: 'pop3-capabilities' (thread: 0x8ba8468) against 
> 2a01:4f8:121:1262::2:110 threw an error!
> ./nselib/pop3.lua:173: bad argument #2 to 'sub' (number expected, got nil)
> stack traceback:
>         [C]: in function 'sub'
>         ./nselib/pop3.lua:173: in function 'capabilities'
>         ./scripts/pop3-capabilities.nse:30: in function 
> <./scripts/pop3-capabilities.nse:29>
>         (...tail calls...)

I checked manually, and this is the response I get:
> ncat -vvv -6 freestuff.gr 110
> Ncat: Version 6.01 ( http://nmap.org/ncat )
> NSOCK (0.0110s) TCP connection requested to 2a01:4f8:121:1262::2:110 
> (IOD #1) EID 8
> NSOCK (0.1550s) Callback: CONNECT SUCCESS for EID 8 
> [2a01:4f8:121:1262::2:110]
> Ncat: Connected to 2a01:4f8:121:1262::2:110.
> NSOCK (0.1560s) Read request from IOD #1 [2a01:4f8:121:1262::2:110] 
> (timeout: -1ms) EID 18
> NSOCK (0.1560s) Read request for 0 bytes from IOD #2 (peer 
> unspecified) EID 26
> NSOCK (0.2970s) Callback: READ SUCCESS for EID 18 
> [2a01:4f8:121:1262::2:110] (76 bytes)
> +OK CommuniGate Pro POP3 Server 5.2.20 ready <15001.1339430446 () aenigma gr>
> NSOCK (0.2970s) Read request for 0 bytes from IOD #1 
> [2a01:4f8:121:1262::2:110] EID 34
> CAPA
> NSOCK (5.0260s) Callback READ SUCCESS for EID 26 (peer unspecified) (5 
> bytes)
> NSOCK (5.0260s) Write request for 5 bytes to IOD #1 EID 43 
> [2a01:4f8:121:1262::2:110]
> NSOCK (5.0260s) Callback: WRITE SUCCESS for EID 43 
> [2a01:4f8:121:1262::2:110]
> NSOCK (5.0260s) Read request for 0 bytes from IOD #2 (peer 
> unspecified) EID 50
> NSOCK (5.1690s) Callback: READ SUCCESS for EID 34 
> [2a01:4f8:121:1262::2:110] (29 bytes)
> +OK capability list follows
> NSOCK (5.1690s) Read request for 0 bytes from IOD #1 
> [2a01:4f8:121:1262::2:110] EID 58
> NSOCK (5.3090s) Callback: READ SUCCESS for EID 58 
> [2a01:4f8:121:1262::2:110] (129 bytes)
> SASL LOGIN PLAIN CRAM-MD5 DIGEST-MD5 GSSAPI MSN NTLM
> STLS
> LAST
> TOP
> USER
> PIPELINING
> UIDL
> IMPLEMENTATION CommuniGatePro
> .
> NSOCK (5.3090s) Read request for 0 bytes from IOD #1 
> [2a01:4f8:121:1262::2:110] EID 66
> QUIT
> NSOCK (8.9930s) Callback READ SUCCESS for EID 50 (peer unspecified) (5 
> bytes)
> NSOCK (8.9930s) Write request for 5 bytes to IOD #1 EID 75 
> [2a01:4f8:121:1262::2:110]
> NSOCK (8.9940s) Callback: WRITE SUCCESS for EID 75 
> [2a01:4f8:121:1262::2:110]
> NSOCK (8.9940s) Read request for 0 bytes from IOD #2 (peer 
> unspecified) EID 82
> NSOCK (9.1400s) Callback: READ SUCCESS for EID 66 
> [2a01:4f8:121:1262::2:110] (51 bytes)
> +OK CommuniGate Pro POP3 Server connection closed
> NSOCK (9.1400s) Read request for 0 bytes from IOD #1 
> [2a01:4f8:121:1262::2:110] EID 90
> NSOCK (9.1400s) Callback: READ EOF for EID 90 [2a01:4f8:121:1262::2:110]
> Ncat: 10 bytes sent, 285 bytes received in 9.15 seconds.
> NSOCK (9.1400s) Callback: READ KILL for EID 82 (peer unspecified)

As you can see from the debug output, the response is sent in a separate 
packet from the "status line", so the pop3 library needs to keep reading 
until a "." is seen.

Dan
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