Security News > 2020 > February > The “Cloud Snooper” malware that sneaks into your Linux servers

TCP source ports only need to be unique for each outbound connection, so most programmers simply let the operating system choose a port number for them, known in the jargon as an ephemeral port.
Most of the time it won't, because the crooks use source port numbers below 10000, while conventional software and most modern operating systems stick to source port numbers of 32768 and above.
For details of the port numbers used and what they are for, please see the full Cloud Snooper report.
There are five TCP source port numbers that the driver watches out for, and one UDP source port number.
Ironically, leaving just TCP source port 9999 unblocked would allow any "Kill payload" commands to get through, thus allowing the crooks to stop the malware but not to start it up again.
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