Researchers from the Great Firewall Report team reported that on the night of August 20 there was either a malfunction or some kind of test underway in the operation of the Great Firewall. All traffic on TCP port 443 was blocked for 74 minutes, effectively cutting China off from most of the global internet.
“From approximately 00:34 to 01:48 (Beijing time, UTC+8) on August 20, 2025, the ‘Great Firewall of China’ exhibited abnormal behavior, unambiguously injecting spoofed TCP RST+ACK packets to terminate any connections on TCP port 443 (both to and from China),” the researchers write.
As a result, Chinese users were unable to access most websites hosted outside the country. The incident also disrupted services that rely on port 443, which is the standard for HTTPS connections. For example, Apple and Tesla use this port to connect to overseas servers that power a number of their core services.
At the same time, analysts note that the fingerprint of the device that carried out this blocking did not match any known node or component of the “Great Firewall of China.”
Researchers believe that this incident was either caused by a new device connected to the Great Firewall of China, or by a known device that “was operating in a new or misconfigured state.”
Thus, the leading theories among experts are that China may have been testing the ability to block connections on port 443, or that someone simply made a mistake that was quickly corrected. However, investigating the incident is difficult due to its brief duration.