The attacker could abuse this connection to the user's system to launch attacks against a user's device.
The initial version of the NAT Slipstreaming attack abused the Session Initiation Protocol (SIP) protocol to establish these pinhole connections to devices on internal networks via ports 5060 and 5061.
Two weeks after the attack became public, Google responded to Kamkar's discovery by blocking these two ports in Chrome 87 to prevent attackers from abusing this technique, which the browser maker deemed a severe threat and easy to abuse.
Apple and Mozilla also shipped similar blocks inside Safari and Firefox weeks later.
New NAT Slipstreaming attack variant discovered
But earlier this week, security researchers from IoT security firm announced that they worked with Kamkar to expand the original attack with a new version they named NAT Slipstreaming 2.0.
This new version replaces SIP and piggybacks on the H.323 multimedia protocol to open the same tunnels inside internal networks and bypass firewalls and NAT tables.
Armis researchers said the 2.0 variant of the NAT Slipstreaming attack was even more dangerous than the first variant as it allowed internet-based attacks on other devices inside the LAN, and not just the user's.
Ports 69, 137, 161, 1719, 1720, 1723, 6566, 10080 to be blocked
Earlier today, Google said that it would block connections to port 1720, used by the H.323 protocol, but also seven other ports that they believe could also be abused in the same manner for other similar variations of the NAT Slipstreaming attack.
The other seven ports were 69, 137, 161, 1719, 1723, 6566, and 10080.
Any HTTP, HTTPS, or FTP connections via these ports will now fail, Google said today.
It appears updating the list of block ports was done server-side without needing to deliver a separate Chrome update to end-users.
Firefox and Microsoft's Edge browsers have also deployed a fix for the NAT Slipstreaming 2.0 attack as well. The Firefox patch was delivered in Firefox 85 earlier this week as CVE-2021-23961, while the Edge fix shipped as a fix for CVE-2020-16043.