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October 16, 2014 20:27
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Drop successful SSLv3 connections using IPtables
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# Matching 'SSL SERVER HELLO' packets using IPtables | |
# Using some connection tracking to make sure not | |
# to match randomly in the middle of some huge SSL | |
# session. | |
iptables --insert INPUT -p tcp --sport 443 \ | |
-m connbytes --connbytes-mode bytes --connbytes-dir both --connbytes 0:500 \ | |
-m state --state ESTABLISHED \ | |
-m length --length 46:375 \ | |
-m u32 --u32 "\ | |
0>>22&0x3C@ 12>>26&0x3C@ 0&0xFFFFFF00=0x16030000 && \ | |
0>>22&0x3C@ 12>>26&0x3C@ 4&0x00FF0000=0x00020000 && \ | |
0>>22&0x3C@ 12>>26&0x3C@ 8&0x00FFFF00=0x00030000" \ | |
-j LOG --log-prefix "SSLv3 Server Hello Handshake" | |
# Results in log messages such as: | |
#SSLv3 Server Hello Handshake |
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"However, in mitigating POODLE, it was shown that the attacker is downgrading the secure connection from TLSv1+ to SSLv3. Does it require to set up a new TCP connection (and thus resetting the counter) for a client to downgrade in protocols?"
I believe that this is required yes. But as I have not seen PCAP data of this part of the attack in progress I cannot be 100% sure.