China's Great Firewall Temporarily Enforces HTTPS Traffic Block
Evaluations based on available data point to an internal cause, such as a setup error or a test of network controls, rather than outside interference.
ASIA — On August 20, 2025, China faced a network disruption that cut off secure connections to services outside its borders for about 74 minutes, starting around 12:34 a.m. Beijing Time.
This occurred through an unconditional block on TCP port 443, the standard network channel for secure web browsing that ensures encrypted data transfer between users and websites.
China's internet censorship system, known as the Great Firewall, inserted forged TCP RST+ACK packets—signals that abruptly end network connections—to stop both incoming and outgoing traffic on this port.
Technical reviews show that the device responsible for the block had features unlike those seen in earlier documented parts of the Great Firewall, such as increasing TCP window sizes in the inserted packets.
The disruption blocked access to many foreign websites and applications that rely on HTTPS, the protocol for secure online communications that protects information like login details and financial transactions.
This affected operations for organizations connected to China, including interruptions to platforms from companies such as Apple and Tesla. Checks during the event confirmed the issue was limited to port 443, with no interference on other common network channels.
Evaluations based on available data point to an internal cause, such as a setup error or a test of network controls, rather than outside interference. The short length of the outage and its focus on one port suggest it was not a planned widespread restriction.
Acronym Index
GFW: Great Firewall
HTTPS: Hypertext Transfer Protocol Secure
IP: Internet Protocol
RST+ACK: Reset + Acknowledge
SYN: Synchronize
SYN+ACK: Synchronize + Acknowledge
TCP: Transmission Control Protocol
TTL: Time to Live