Comware

 View Only
last person joined: 2 days ago 

Back to discussions
Expand all | Collapse all

ssh KEX methods

This thread has been viewed 10 times

  • 1.  ssh KEX methods

    Posted Jan 11, 2022 11:51 AM
    Hi

    Does anyone know if it's possible to configure key exchange methods for ssh?  I have an A5500 EI switch that's throwing up vulnerabilities on our scanner because of this (see details below).

    Thanks in advance

    Details
    Technical Details
    The remote SSH server supports the following DHE KEX algorithm(s):

    diffie-hellman-group1-sha1 diffie-hellman-group14-sha1 diffie-hellman-group-exchange-sha1

    External Sources
    The following external sources can help provide some more information on this vulnerability

    https://www.researchgate.net/profile/Anton-Stiglic-2/publication/2401745_Security_Issues_in_the_Diffie-Hellman_Key_Agreement_Protocol

    https://github.com/Balasys/dheater

    Detection
    Checks the supported KEX algorithms of the remote SSH server.

    CVEs
    This vulnerability covers the following CVEs:

    CVE-2002-20001

    ------------------------------
    Keith Chalmers
    ------------------------------


  • 2.  RE: ssh KEX methods
    Best Answer

    EMPLOYEE
    Posted Jan 11, 2022 12:42 PM
    Hi Keith,

    According documentation for 5500 you cannot change KEX method for SSH server. You can only decide which method to use when you initiate SSH sessions to remote servers from the 5500 itself (e.g. when you use 5500 as a SSH client), but even in this case your choice is limited:

    - diffie-hellman-group-exchange-sha1
    - diffie-hellman-group1-sha1
    - diffie-hellman-group14-sha1

    You can see syntax of 'ssh2' command for more details. Seems like this device supports only those 3 DH groups and nothing more. Therefore even if KEX method change for a local server would be possible I don't think you can mitigate this vulnerability with the DH groups supported, neither of these will help you as CVE-2002-20001 recommends DHE key exchange method to be disabled and the Elliptic Curve Diffie-Hellman method to be used as a workaround. And seems 5500 doesn't support ECDHE, at least I couldn't find any reference to it.

    Just my 2 cents, totally personal opinion: Management interfaces of network infrastructure devices normally are separated in an OOB network, so chances some of authorized personell will want to exploit this vulnerability is quite low... Also, this switch is EoL, I mention it to set realistic expectations about a patch taking into account this CVE has been created just couple of months ago.


    ------------------------------
    Ivan Bondar
    ------------------------------

    Original Message


  • 3.  RE: ssh KEX methods

    Posted Jan 11, 2022 12:55 PM
    Hi Ivan

    Many thanks for your reply - I had a feeling that there may not have been a fix based on the research I had done, but it's good to have an expert confirm it!  You are right - our management network is segregated from the "production" network, so at least the risk is mitigated.

    Kind regards
    Keith

    ------------------------------
    Keith Chalmers
    ------------------------------

    Original Message