The sshd process is having high CPU load

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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.