The sshd process is having high CPU load

This document (000019812) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server SLES 12 SP5
SUSE Linux Enterprise Server SLES 12 SP4 LTSS

Situation

After patching openssh to version 7.2p2-78.4.2, the sshd process can cause high CPU load.

The very high CPU consumption can be seen in the supportconfig data of the affected server.
For example:

# Top 10 CPU Processes
%CPU   PID USER     CMD
90.3  8014 root     sshd: [accepted]
...


# /bin/ps axwwo user,pid,ppid,%cpu,%mem,vsz,rss,stat,time,cmd
USER       PID  PPID %CPU %MEM    VSZ   RSS STAT     TIME CMD
...
root      8014  7761 90.4  0.0  72880  6940 Rs   00:00:34 sshd: [accepted]

 

Resolution

Update openssh to version 7.2p2-78.7.1 or later to resolve this issue. The version fixing the issue is the same on both SLES12 SP4 LTSS and SLES12 SP5.
 

Cause

This is a bug in openssh version 7.2p2-78.4.2 when specific encryption algorithms are used.

Status

Reported to Engineering

Additional Information

The same issue can be reproduced by connecting a ssh client to the ssh server with a specific encryption algorithm:
For example:
  ssh -o kexalgorithms=diffie-hellman-group-exchange-sha256 root@server-name

Disclaimer

This Support Knowledgebase provides a valuable tool for SUSE customers and parties interested in our products and solutions to acquire information, ideas and learn from one another. Materials are provided for informational, personal or non-commercial use within your organization and are presented "AS IS" WITHOUT WARRANTY OF ANY KIND.

  • Document ID:000019812
  • Creation Date: 11-Feb-2021
  • Modified Date:11-Feb-2021
    • SUSE Linux Enterprise Server

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