[Bro] Bro bug?

Hank Leininger hlein at korelogic.com
Sun Jan 19 10:38:40 PST 2014

On Sun, Jan 19, 2014 at 12:46:31PM -0500, Justin Azoff wrote:
> On Sun, Jan 19, 2014 at 05:22:10PM +0000, Kellogg, Brian D (OLN) wrote:
> > 1390143300.845103	Cma6473thsxripFj9k	3326	80	tcp	-	0.092641	1056737769	0	RSTOS0	T	0	SaR	2	88	1	40	(empty)	-	US	so-eth0
> So, with the field names, that is:
> duration 0.092641
> orig_bytes 1056737769
> resp_bytes 0
> conn_state RSTOS0
> local_orig T
> missed_bytes 0
> history SaR

> Which shows that bro calculated that there were 1056737769 bytes based
> on sequence numbers, but only actually saw 88 bytes.
> I think simply changing $size to $num_bytes_ip will fix your problems.

That's probably a decent workaround.

Another option would be to only trigger on connections that were fully
established - with conn_state of SF (possibly also RST0 and RSTR) - as
those should have the "most reliable" byte counts.

I think the problem in Brian's case comes from this not being a normally
established / torn down connection.  conn_state RSTOS0 implies Bro saw
an incomplete connection attempt be torn down by an RST (by the orignal
sender, which is odd, and history SaR means the receiver sent not a
SYNACK, and not nothing, but a bare ACK, which is odder still... but
that is a story for another day*).

It could be argued that Bro should "know" that for certain failed /
incomplete connection types, ACK/SEQ math can be unreliable (maybe it
already does for some), and that SaR is a candidate for that (maybe that
has already been argued; there's probably good cases to be made both

[ *Snip esoteric ramble about the 4 way handshake, etc. ]


Hank Leininger <hlein at korelogic.com>
D24D 2C2A F3AC B9AE CD03  B506 2D57 32E1 686B 6DB3
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