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-258002r1155590_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. Compression options are: no - disables compression delayed - allow compression only after authentication yes - enables compression before authentication, which can leak sensitive metadata and is not recommended | ||||
| STIG | Date | |||
| Red Hat Enterprise Linux 9 Security Technical Implementation Guide | 2026-02-05 | |||
Related Frameworks
4 paths across 3 frameworks
Related Frameworks
NIST 800-531 mapping
CM-6
1.00
- DISA · V2R8 · disa_xccdf · related
- DISA · 2025-01-23 · disa_cci_list · equivalent
NIST 800-1712 mappings
3.4.1
1.00
- DISA · V2R8 · 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 · V2R8 · 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 · V2R8 · disa_xccdf · related
Details
Check Text (C-258002r1155590_chk)
Verify the RHEL 9 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'
/etc/ssh/sshd_config:Compression no
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