FreeBSD 8.2-STABLE sending FIN no ACK packets. kern/168842

[Andre Oppermann]

On 08.06.2012 14:43, Nikolay Denev wrote:
>
> On Jun 8, 2012, at 4:30 AM, Adrian Chadd wrote:
>
>> On 7 June 2012 05:41, Nikolay Denev<ndenev at gmail.com>  wrote:
>>> Hello,
>>>
>>> I've been pointed out by our partner that we are sending TCP packets with FIN flag and no ACK set, which is triggering
>>> alerts on their firewalls.
>>> I've investigated, and it appears that some of our FreeBSD hosts are really sending such packets. (they are running some java applications)
>>> I did "tcpdump -s0 -vni em1 '(tcp[tcpflags]&  tcp-ack == 0)&&  (tcp[tcpflags]&  tcp-fin != 0)'" to catch them.
>>>
>>> Is this considered normal?
>>> It seems at least Juniper considers this malicious traffic : http://www.juniper.net/techpubs/software/junos-security/junos-security10.0/junos-security-swconfig-security/id-72577.html
>>
>> Would you please file a PR with this, so it doesn't get lost?
>>
>> Thanks,
>>
>>
>> Adrian
>
> Filed as kern/168842, and mistakenly duplicated as kern/168843 (the latter can be closed).
>
> As I wrote in the PR, I have a PCAP that I can privately share if someone is interested.

Hi Nikolay

please make the pcap available to me.  From the tcpdump in the PR I can't
analyze how this stray packet may come about.

While certainly a bug it is not a security issue as any compliant tcp stack
would drop such a packet on receipt.

-- 
Andre