Security Advisory

Published: October 31, 2022
Last Update: October 31, 2022

From 2018 - 2020, several vulnerabilities were disclosed that could expose OpenSSH SCP clients to attacks by Man-in-the-Middle (MITM) and/or malicious SCP servers. These vulnerabilities could affect SCP file transfer operations initiated from the management of ACOS devices and are addressed in this document.

Item Score
# Vulnerability ID Source Score Summary
1 CVE-2020-14145 CVSSv3 5.9 Med openssh: Observable discrepancy leading to an information leak in the algorithm negotiation[1]
2 CVE-2019-6111 CVSSv3 5.9 Med openssh: Improper validation of object names allows malicious server to overwrite files via scp client[2]
3 CVE-2019-6110 CVSSv3 6.8 Med openssh: Acceptance and display of arbitrary stderr allows for spoofing of scp client output[3]
4 CVE-2019-6109 CVSSv3 6.8 Med openssh: Missing character encoding in progress display allows for spoofing of scp client output[4]
5 CVE-2018-20685 CVSSv3 5.3 Med openssh: scp client improper directory name validation[5]
Affected Releases

The table below indicates releases of ACOS exposed to this vulnerability and ACOS releases that address them. ACOS release families not indicated below are unaffected by these vulnerabilities.

Customers using affected ACOS releases can overcome vulnerability exposures by updating to the indicated resolved release. If the table does not list a corresponding resolved or unaffected release, then no ACOS release update is currently available.

Releases Affected Releases Resolved or Unaffected
5.1.0 – 5.2.1-Px None
5.0.1-TPS – 5.0.2-TPS-Px None
4.1.4-GR1 – 4.1.4-GR1-Px None
3.2.5 – 3.2.5-Px None
Workarounds and Mitigations

These vulnerabilities involve malicious or MITM SCP servers for exploitation. Manage and configure ACOS devices for SCP file transfer operations only with trusted SCP servers on trusted communication channels.

Alternately, manage and configure ACOS devices for file transfer operations using methods other than SCP. Other ACOS secure file transfer methods available include SFTP and HTTPS, which are not exposed to these vulnerabilities.

Software Updates

Software updates that address these vulnerabilities are or will be published at the following URL: https://support.a10networks.com/

Vulnerability Details

The following table shares brief descriptions for the vulnerabilities addressed in this document.

Vulnerability ID Vulnerability Description

The client side in OpenSSH 5.7 through 8.4 has an Observable Discrepancy leading to an information leak in the algorithm negotiation. This allows man-in-the-middle attackers to target initial connection attempts (where no host key for the server has been cached by the client). NOTE: some reports state that 8.5 and 8.6 are also affected.


An issue was discovered in OpenSSH 7.9. Due to the scp implementation being derived from 1983 rcp, the server chooses which files/directories are sent to the client. However, the scp client only performs cursory validation of the object name returned (only directory traversal attacks are prevented). A malicious scp server (or Man-in-The-Middle attacker) can overwrite arbitrary files in the scp client target directory. If recursive operation (-r) is performed, the server can manipulate subdirectories as well (for example, to overwrite the .ssh/authorized_keys file).


In OpenSSH 7.9, due to accepting and displaying arbitrary stderr output from the server, a malicious server (or Man-in-The-Middle attacker) can manipulate the client output, for example to use ANSI control codes to hide additional files being transferred.


An issue was discovered in OpenSSH 7.9. Due to missing character encoding in the progress display, a malicious server (or Man-in-The-Middle attacker) can employ crafted object names to manipulate the client output, e.g., by using ANSI control codes to hide additional files being transferred. This affects refresh_progress_meter() in progressmeter.c.


In OpenSSH 7.9, scp.c in the scp client allows remote SSH servers to bypass intended access restrictions via the filename of . or an empty filename. The impact is modifying the permissions of the target directory on the client side.



Modification History
Revision Date Description
1.0 October 31, 2022

Initial Publication

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