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0001768: drop new connections without syn-flag via default-ruleset - MantisBT Endian Bugtracker
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IDProjectCategoryView StatusDate SubmittedLast Update
0001768Endian FirewallFirewall (iptables)public2009-04-13 13:102009-06-10 11:01
Assigned Topeter-endian 
PlatformOSOS Version
Product Version2.2-rc3 
Target VersionFixed in Version 
Summary0001768: drop new connections without syn-flag via default-ruleset
Descriptioniptables command:
-p tcp ! --syn -m state --state NEW -j DROP

tcp flags:!SYN,RST,ACK/SYN state NEW
tcp flags:!0x16/0x02 state NEW
Additional Informationwe want connections to use the correct handshake using sys, syn ack, ack

initial (new) connections must have the syn-flag set
otherwise we drop the connection as we are stateful
TagsNo tags attached.
Attached Files

- Relationships
related to 0001515closedpeter-endian zonefw: --state NEW check blocks communication to clients behind a router due to triangle connection 

-  Notes
mike-f (updater)
2009-04-13 13:19

for the green-IF we implemented a reject-rule
(we don't want to wait for a timeout on our clients)

-p tcp ! --syn -m state --state NEW -i eth0 -j REJECT
-p tcp ! --syn -m state --state NEW -i br0 -j REJECT
peter-endian (administrator)
2009-04-14 10:57

this was in fact so before, but it causes problems when you have a triangle communication where replies don't pass the same path as requests.

If you have a router behind a zone you have exactly that constellation and that's a pretty usual scenario.
mike-f (updater)
2009-04-14 12:34

referencing bug id 1515? [^]

somehow not very clear to me:
in that constellation you use the same nets on different interfaces?

have to reply here as the other bug is closed
peter-endian (administrator)
2009-04-14 19:29

made 0001515 more clear.

for the vpn firewall (enterprise version) it's even more complicated, since you can have multiple vpn's connected to same sites causing a loop, where it is legitime to have requests using one path and responses another one.

i think the best solution would be to make NewNotSyn checks configurable through the rule editor or global option for each firewall section
mike-f (updater)
2009-04-14 19:34

some kind of "lockdown-button" sounds good

- Issue History
Date Modified Username Field Change
2009-04-13 13:10 mike-f New Issue
2009-04-13 13:10 mike-f Assigned To => peter-endian
2009-04-13 13:19 mike-f Note Added: 0002135
2009-04-14 10:57 peter-endian Note Added: 0002138
2009-04-14 12:34 mike-f Note Added: 0002142
2009-04-14 19:25 peter-endian Relationship added related to 0001515
2009-04-14 19:29 peter-endian Note Added: 0002148
2009-04-14 19:34 mike-f Note Added: 0002149
2009-06-10 11:01 peter-endian Severity minor => feature

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