From 0e233601c91f8c8797e5501ed51ded91502d58c9 Mon Sep 17 00:00:00 2001
From: Pierre LALET <pierre.lalet@cea.fr>
Date: Tue, 7 Mar 2017 21:12:36 +0100
Subject: [PATCH] Accept TCP RST packets with .ack == 0 as answers
Without this code, when an out of connection TCP packet receives a
TCP answer with flag RST and the ack set to 0, it is not seen as an
answer.
This comes without regression tests because I have been unable to
find a reliable machine without firewall on the Internet.
Simple test, if 192.168.0.1 has no firewall:
>>> sr(IP(dst="192.168.0.1")/TCP(sport=80, dport=12345, flags='SA'),
... timeout=2)
This test will not terminate without this patch.
---
scapy/layers/inet.py | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/scapy/layers/inet.py b/scapy/layers/inet.py
index 7d07e67d..b1c04232 100644
--- a/scapy/layers/inet.py
+++ b/scapy/layers/inet.py
@@ -525,7 +525,12 @@ class TCP(Packet):
if not ((self.sport == other.dport) and
(self.dport == other.sport)):
return 0
- if (abs(other.seq-self.ack) > 2+len(other.payload)):
+ if abs(other.ack - self.seq) > 2:
+ return 0
+ # Do not check ack value for RST packets when ack is 0
+ if self.flags.R and not self.ack:
+ return 1
+ if abs(other.seq - self.ack) > 2 + len(other.payload):
return 0
return 1
def mysummary(self):
--
GitLab