China cut itself off from much of the global internet for just over an hour on Wednesday.
Activist group Great Firewall Report spotted the outage, which it said disrupted all traffic to TCP port 443 – the standard port used for carrying HTTPS traffic.
“Between approximately 00:34 and 01:48 (Beijing Time, UTC+8) on August 20, 2025, the Great Firewall of China (GFW) exhibited anomalous behavior by unconditionally injecting forged TCP RST+ACK packets to disrupt all connections on TCP port 443,” the group wrote in a Wednesday post.
That disruption meant Chinese netizens couldn’t reach most websites hosted outside China, which is inconvenient. The incident also blocked other services that rely on port 443, which could be more problematic because many services need to communicate with servers or sources of information outside China for operational reasons. For example, Apple and Tesla use the port to connect to offshore servers that power some of their basic services.
China sometimes cranks up censorship during events it doesn’t want its population to know about. The Register is unaware of any such event that took place during this outage.
Therefore, there’s no obvious reason China decided to block port 443.
The Great Firewall Report thinks the device that implemented the block “does not match the fingerprints of any known GFW devices.”
The group therefore thinks the incident “was caused by either a new GFW device or a known device operating in a novel or misconfigured state.” So perhaps China was either testing its ability to block port 443 – which Beijing might see as a useful capability – or someone messed up.
This is not the Great Firewall’s first glitch. We’ve seen it leaking a little info, and leaving itself open to attack. China’s overall censorship regime is also imperfect, due to both technical and bureaucratic bungling.
If asked nicely, China will share the tech behind the Great Firewall with other nations. The Register mentions that because Pakistan is thought to have implemented its own version of the Firewall and, according to internet monitoring firm NetBlocks, experienced a huge drop in local internet traffic a few hours before the port 443 incident in China. ®