RHEL 9 must not allow users to override SSH environment variables.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-257993 | RHEL-09-255085 | SV-257993r1045049_rule | CCI-000366 | medium |
| Description | ||||
| SSH environment options potentially allow users to bypass access restriction in some configurations. | ||||
| STIG | Date | |||
| Red Hat Enterprise Linux 9 Security Technical Implementation Guide | 2025-05-14 | |||
Details
Check Text (C-257993r1045049_chk)
Verify that unattended or automatic logon via SSH is disabled with the following command:
$ sudo /usr/sbin/sshd -dd 2>&1 | awk '/filename/ {print $4}' | tr -d '\r' | tr '\n' ' ' | xargs sudo grep -iH '^\s*permituserenvironment'
PermitUserEnvironment no
If "PermitUserEnvironment" is set to "yes", is missing completely, or is commented out, this is a finding.
If the required value is not set, this is a finding.
Fix Text (F-61658r1045048_fix)
Configure the RHEL 9 SSH daemon to not allow unattended or automatic logon to the system by editing the following line in the "/etc/ssh/sshd_config" or in a file in "/etc/ssh/sshd_config.d":
PermitUserEnvironment no
Restart the SSH daemon for the setting to take effect:
$ sudo systemctl restart sshd.service