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Something is blocking on incoming connections on my Mac and I can't figure out what it is. Firewall is turned off, anti virus is turned off.

As a simple test, I'm executing:

shai@Macbook Downloads $ nc -l 10.0.0.12 12345

I can't access it from my iPhone (using the same WiFi hotspot), but when using a browser locally, I see output on netcat - which means connection succeeded.

What is going on?

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    As you answered your own question, I suggest you flag this post and ask some kind moderator to undo your bounty, so you can use your reputation in future posts.
    – harrymc
    Jan 27, 2014 at 14:19
  • We typically don't do this, but given that the bounty was only started yesterday, consider this a freebie.
    – slhck
    Jan 28, 2014 at 8:54

1 Answer 1

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I decided to go over all of the log files I could find under /var/logs.

At some point, I ended up in a log file that contains DENY/ALLOW output for incoming connections. I then used lsof to figure out who's writing to that file and found the reason for this whole mess: Checkpoint Endpoint security, a VPN client that has a built-in security policy thing.

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    Thanks, eventually, I found the same problem, after one day of struggle, and in 2021! I was happening this despite the VPN client (and its Firewall) was disabled. It seems sometimes it leaves things in an inconsistent state: community.checkpoint.com/t5/Endpoint/…
    – zakmck
    Apr 10, 2021 at 19:37
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    The app might be called "Endpoint Security VPN" and I can confirm that despite saying its firewall was off, it was indeed blocking incoming connections. Bad engineers. Uninstall it with the script hidden in /Library/Application Support/Checkpoint/Endpoint Connect/uninstall
    – John White
    Apr 3, 2022 at 9:15
  • The problem is fixed in the latest client versions. I had the problem with E82 client and after upgrade to E87 the problem has gone.
    – FoxyBOA
    Aug 12, 2023 at 7:41

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