Security Bulletin: IBM MQ Appliance vulnerable to "Terrapin" attack in OpenSSH (CVE-2023-48795)

Summary

By manipulating sequence numbers during SSH connection setup, a MITM attacker can delete negotiation messages without causing a MAC failure. To mitigate this vulnerability, IBM MQ Appliance has removed the chacha20-poly1305 cipher and all etm HMACs from the default set of algorithms offered,

Vulnerability Details

CVEID:CVE-2023-48795
**DESCRIPTION:**OpenSSH is vulnerable to a machine-in-the-middle attack, caused by a flaw in the extension negotiation process in the SSH transport protocol when used with certain OpenSSH extensions. A remote attacker could exploit this vulnerability to launch a machine-in-the-middle attack and strip an arbitrary number of messages after the initial key exchange, breaking SSH extension negotiation and downgrading the client connection security.
CVSS Base score: 5.9
CVSS Temporal Score: See: https://exchange.xforce.ibmcloud.com/vulnerabilities/275282 for the current score.
CVSS Vector: (CVSS:3.0/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N)

Affected Products and Versions

Remediation/Fixes

This vulnerability is addressed under APAR IT46266

IBM strongly recommends addressing the vulnerability now.

IBM MQ Appliance version 9.3 LTS

Apply IBM MQ Appliance 9.3.0.20 fix pack, or later firmware.

IBM MQ Appliance version 9.3 CD

Apply IBM MQ Appliance 9.3.5.2 cumulative security update, or later firmware.

Workarounds and Mitigations

The fix removes the Chacha20-poly1305 cipher and the etm HMAC algorithms from the default set, which avoids the vulnerability. Customers may perform this same mitigation on earlier firmware versions, and should also remove these algorithms from any custom SSH configuration already deployed.

If the affected cipher and or HMACs are required for interoperability, they can be listed at the end of the cipher and MAC lists, so that they will only be used if no stronger algorithms are supported by client and server.