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Researchers from the Great Firewall Report team noticed that on the night of August 20, China’s Great Firewall experienced a technical issue or was undergoing some type of testing. All traffic on TCP port 443 was blocked for 74 minutes, isolating China from nearly the entire global Internet.
“From approximately 00:34 to 01:48 (Beijing Time, UTC+8) on August 20, 2025, the Great Firewall of China exhibited anomalous behavior, unconditionally injecting fake TCP RST+ACK packets to terminate all connections on TCP port 443 (both to and from China),” the researchers wrote.
This prevented Chinese users from accessing most websites hosted overseas. The incident also blocked services using port 443, the standard for HTTPS connections. Apple and Tesla, for example, use this port to connect to foreign servers that provide some of their core services.
At the same time, analysts note that the fingerprint of the device that implemented this block did not match any known node or component of the “Great Firewall of China.”
Researchers believe the incident was caused by a new device connected to the Great Firewall of China or an existing device “running in a new or incorrectly configured state.”
Therefore, leading theories among experts are that China may have been testing the possibility of blocking connections on port 443, or that someone simply made a mistake that was quickly corrected. However, the investigation into the incident is difficult due to the short duration of the incident.
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