OpenSSH Arbitrary stderr Output Man-in-the-Middle Vulnerability [CVE-2019-6110]

CVE Number – CVE-2019-6110

A vulnerability in the Secure Copy Protocol (SCP) client utility of OpenSSH could allow an unauthenticated, remote attacker to conduct a man-in-the-middle attack on a targeted system.The vulnerability is due to the affected software accepting and displaying arbitrary stderr output. An attacker on an attacker-controlled SCP server or an attacker who is able to conduct a man-in-the-middle attack could exploit this vulnerability by persuading a targeted user on an SCP client to connect to the attacker-controlled server. If successful, the attacker could use American National Standards Institute (ANSI) control codes to employ malicious object names designed to manipulate the output of a targeted SCP client.The OpenBSD Project has confirmed the vulnerability and released software updates.


  • To exploit this vulnerability, an attacker must be able to perform a man-in-the-middle attack or persuade a user on a targeted SCP client to connect to an attacker-controlled SCP server. These requirements may reduce the likelihood of a successful exploit.


  • Administrators are advised to apply the appropriate updates.Administrators are advised to allow only trusted users to have network access.Administrators are advised to use an unprivileged account when browsing the Internet.Administrators are advised to monitor critical systems.Users are advised not to open email messages from suspicious or unrecognized sources. If users cannot verify that links or attachments included in email messages are safe, they are advised not to open them.Users are advised not to visit websites or follow links that have suspicious characteristics or cannot be verified as safe.

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Duncan Newell

Duncan is a technology professional with over 20 years experience of working in various IT roles. He has a interest in cyber security, and has a wide range of other skills in radio, electronics and telecommunications.

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