RHEL 9 SSH daemon must not allow compression or must only allow compression after successful authentication.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-258002 | RHEL-09-255130 | SV-258002r991589_rule | CCI-000366 | medium |
| Description | ||||
| If compression is allowed in an SSH connection prior to authentication, vulnerabilities in the compression software could result in compromise of the system from an unauthenticated connection, potentially with root privileges. | ||||
| STIG | Date | |||
| Red Hat Enterprise Linux 9 Security Technical Implementation Guide | 2025-05-14 | |||
Related Frameworks
4 paths across 3 frameworks
Related Frameworks
NIST 800-531 mapping
CM-6
1.00
- DISA · 2 · disa_xccdf · related
- DISA · 2025-01-23 · disa_cci_list · equivalent
NIST 800-1712 mappings
3.4.1
1.00
- DISA · 2 · disa_xccdf · related
- DISA · 2025-01-23 · disa_cci_list · equivalent
- NIST · Rev 2 (Feb 2020, errata Jan 2021) · nist_800_171_app_d · equivalent
3.4.2
1.00
- DISA · 2 · disa_xccdf · related
- DISA · 2025-01-23 · disa_cci_list · equivalent
- NIST · Rev 2 (Feb 2020, errata Jan 2021) · nist_800_171_app_d · equivalent
CCI1 mapping
CCI-000366
1.00
- DISA · 2 · disa_xccdf · related
Details
Check Text (C-258002r991589_chk)
Verify the SSH daemon performs compression after a user successfully authenticates 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*compression'
Compression delayed
If the "Compression" keyword is set to "yes", is missing, or the returned line is commented out, this is a finding.
Fix Text (F-61667r925992_fix)
Configure the SSH daemon to not allow compression.
Uncomment the "Compression" keyword in "/etc/ssh/sshd_config" on the system and set the value to "delayed" or "no":
Compression no
The SSH service must be restarted for changes to take effect:
$ sudo systemctl restart sshd.service