Connections to HTTP, HTTPS or FTP servers on port 554 will fail. This is a mitigation for the NAT Slipstream 2.0 attack. It helps developers by keeping the web platform safe for users. Chrome briefly blocked port 554 before, but it was unblocked due to complaints from enterprise users. However, we have now achieved rough consensus at to block 554.


Some NAT routers and firewall products inspect traffic on port 554 and use it as instructions to open UDP forwarding back to the original host running the browser. Other browsers have blocked port 554, and statistics collection indicates that use of port 554 for HTTP is in fact minimal. On the dev channel it is used for approximately 0.00003% of requests.


Specification link

Specification being incubated in a Community Group

Status in Chromium


Enabled by default

Consensus & Standardization

After a feature ships in Chrome, the values listed here are not guaranteed to be up to date.

  • Shipped/Shipping
  • Shipped/Shipping
  • No signals


Last updated on 2022-01-14