Re: unused bit attack alert

[vern () EE LBL GOV (Vern Paxson)]

> LigerTeam, strongly propose inserting of
> solution code before the computing of flag
> variable.
>
>   flag = flags & 0x3f;

The more robust fix is to systematically test for TCP flags by masking
to the value being tested.  For example:

        #define TEST_FLAGS(flags, mask) (((flags) & (mask)) == (mask))

Otherwise you are still vulnerable to attackers setting legitimate flags
in bogus combinations, such as adding URG to a SYN.

                Vern