Threat Level: green Handler on Duty: Brad Duncan

SANS ISC: Remote Desktop Protocol (RDP) Discovery - SANS Internet Storm Center SANS ISC InfoSec Forums

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Remote Desktop Protocol (RDP) Discovery

I have noticed a surge in probe against the RDP service in the past 2 weeks. In August, a remote code execution (RCE) critical patch was released to fix an exploit related to CVE-2021-34535 which include a POC to exploit this vulnerability. This vulnerability is also affecting Microsoft Hyper-V Manager “Enhanced Session Mode” [5] and Microsoft Defender’s Application Guard (WDAG) [6].

According to Shodan [7], there are over 4.89M IPs with TCP:3389 listening and over 3.9M IPs with RDP listening on other ports but mainly on 3388 [8]. Beside TCP:3389, my honeypot logged mstshash probe against other port such as 21, 23, 80, 8000, 8080.

20211018-022140: data
\x03\x00\x00+&\xe0\x00\x00\x00\x00\x00Cookie: mstshash=hello\r\n\x01\x00\x08\x00\x03\x00\x00\x00

[2021-10-30 08:42:54] [1558] [ftp_21_tcp 16145] [] recv: .../*......Cookie: mstshash=Administr

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If using RDP, Microsoft provided the following information on "Security guidance for remote desktop adoption".


Guy Bruneau IPSS Inc.
My Handler Page
Twitter: GuyBruneau
gbruneau at isc dot sans dot edu


523 Posts
ISC Handler
Oct 30th 2021
Why do people connect RD directly to the internet? In today's environment it is fairly straight forward to setup an OpenVPN server in conjunction with a pfsense firewall. Then you add a significant layer of security to your facilities that is difficult to peal away remotely.

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